Unusual Amino Acids in Medicinal Chemistry

Non-canonical amino acid bioincorporation into antimicrobial peptides and its challenges

The rise of antimicrobial resistance and multi-drug resistant pathogens has necessitated explorations for novel antibiotic agents as the discovery of conventional antibiotics is becoming economically less viable and technically more challenging for biopharma. Antimicrobial peptides (AMPs) have emerged as a promising alternative because of their particular mode of action, broad spectrum and difficulty that microbes have in becoming resistant to them. The AMPs bacitracin, gramicidin, polymyxins and daptomycin are currently used clinically. However, their susceptibility to proteolytic degradation, toxicity profile, and complexities in large-scale manufacture have hindered their development. To improve their proteolytic stability, methods such as integrating non-canonical amino acids (ncAAs) into their peptide sequence have been adopted, which also improves their potency and spectrum of action. The benefits of ncAA incorporation have been made possible by solid-phase peptide synthesis. However, this method is not always suitable for commercial production of AMPs because of poor yield, scale-up difficulties, and its non-'green' nature. Bioincorporation of ncAA as a method of integration is an emerging field geared towards tackling the challenges of solid-phase synthesis as a green, cheaper, and scalable alternative for commercialisation of AMPs. This review focusses on the bioincorporation of ncAAs; some challenges associated with the methods are outlined, and notes are given on how to overcome these challenges. The review focusses particularly on addressing two key challenges: AMP cytotoxicity towards microbial cell factories and the uptake of ncAAs that are unfavourable to them. Overcoming these challenges will draw us closer to a greater yield and an environmentally friendly and sustainable approach to make AMPs more druggable.

Discovery and Characterization of Pyridoxal 5'-Phosphate-Dependent Cycloleucine Synthases

Pyridoxal 5'-phosphate (PLP)-dependent enzymes are the most versatile biocatalysts for synthesizing nonproteinogenic amino acids. α,α-Disubstituted quaternary amino acids, such as 1-aminocyclopentane-1-carboxylic acid (cycloleucine), are useful building blocks for pharmaceuticals. In this study, starting with the biosynthesis of fusarilin A, we discovered a family of PLP-dependent enzymes that can facilitate tandem carbon-carbon forming steps to catalyze an overall [3 + 2]-annulation. In the first step, the cycloleucine synthases use SAM as the latent electrophile and an in situ-generated enamine as the nucleophile for γ-substitution. Whereas previously characterized γ-replacement enzymes protonate the resulting α-carbon and release the acyclic amino acid, cycloleucine synthases can catalyze an additional, intramolecular aldol or Mannich reaction with the nucleophilic α-carbon to form the substituted cyclopentane. Overall, the net [3 + 2]-annulation reaction can lead to 2-hydroxy or 2-aminocycloleucine products. These studies further expand the biocatalytic scope of PLP-dependent enzymes.

Synergistic Photoenzymatic Catalysis Enables Synthesis of a-Tertiary Amino Acids Using Threonine Aldolases

a-Tertiary amino acids are essential components of drugs and agrochemicals, yet traditional syntheses are step-intensive and provide access to a limited range of structures with varying levels of enantioselectivity. Here, we report the α-alkylation of unprotected alanine and glycine by pyridinium salts using pyridoxal (PLP)-dependent threonine aldolases with a Rose Bengal photoredox catalyst. The strategy efficiently prepares various a-tertiary amino acids in a single chemical step as a single enantiomer. UV-vis spectroscopy studies reveal a ternary interaction between the pyridinium salt, protein, and photocatalyst, which we hypothesize is responsible for localizing radical formation to the active site. This method highlights the opportunity for combining photoredox catalysts with enzymes to reveal new catalytic functions for known enzymes.

Asymmetric synthesis of unnatural α-amino acids through photoredox-mediated C-O bond activation of aliphatic alcohols

Unnatural α-amino acids constitute a fundamental class of biologically relevant compounds. However, despite the interest in these motifs, synthetic strategies have traditionally employed polar retrosynthetic disconnections. These methods typically entail the use of stoichiometric amounts of toxic and highly sensitive reagents, thereby limiting the substrate scope and practicality for scale up. In this work, an efficient protocol for the asymmetric synthesis of unnatural α-amino acids is realized through photoredox-mediated C-O bond activation in oxalate esters of aliphatic alcohols as radical precursors. The developed system uses a chiral glyoxylate-derived N-sulfinyl imine as the radical acceptor and allows facile access to a range of functionalized unnatural α-amino acids through an atom-economical redox-neutral process with CO2 as the only stoichiometric byproduct.

Applications of genetic code expansion technology in eukaryotes

Unnatural amino acids (UAAs) have gained significant attention in protein engineering and drug development owing to their ability to introduce new chemical functionalities to proteins. In eukaryotes, genetic code expansion (GCE) enables the incorporation of UAAs and facilitates posttranscriptional modification (PTM), which is not feasible in prokaryotic systems. GCE is also a powerful tool for cell or animal imaging, the monitoring of protein interactions in target cells, drug development, and switch regulation. Therefore, there is keen interest in utilizing GCE in eukaryotic systems. This review provides an overview of the application of GCE in eukaryotic systems and discusses current challenges that need to be addressed.

Photocatalytic Functionalization of Dehydroalanine-Derived Peptides in Batch and Flow

Unnatural amino acids, and their synthesis by the late-stage functionalization (LSF) of peptides, play a crucial role in areas such as drug design and discovery. Historically, the LSF of biomolecules has predominantly utilized traditional synthetic methodologies that exploit nucleophilic residues, such as cysteine, lysine or tyrosine. Herein, we present a photocatalytic hydroarylation process targeting the electrophilic residue dehydroalanine (Dha). This residue possesses an α,β-unsaturated moiety and can be combined with various arylthianthrenium salts, both in batch and flow reactors. Notably, the flow setup proved instrumental for efficient scale-up, paving the way for the synthesis of unnatural amino acids and peptides in substantial quantities. Our photocatalytic approach, being inherently mild, permits the diversification of peptides even when they contain sensitive functional groups. The readily available arylthianthrenium salts facilitate the seamless integration of Dha-containing peptides with a wide range of arenes, drug blueprints, and natural products, culminating in the creation of unconventional phenylalanine derivatives. The synergistic effect of the high functional group tolerance and the modular characteristic of the aryl electrophile enables efficient peptide conjugation and ligation in both batch and flow conditions.

Enantioselective organocatalytic strategies to access noncanonical α-amino acids

Organocatalytic asymmetric synthesis has evolved over the years and continues to attract the interest of many researchers worldwide. Enantiopure noncanonical amino acids (ncAAs) are valuable building blocks in organic synthesis, medicinal chemistry, and chemical biology. They are employed in the elaboration of peptides and proteins with enhanced activities and/or improved properties compared to their natural counterparts, as chiral catalysts, in chiral ligand design, and as chiral building blocks for asymmetric syntheses of complex molecules, including natural products. The linkage of ncAA synthesis and enantioselective organocatalysis, the subject of this perspective, tries to imitate the natural biosynthetic process. Herein, we present contemporary and earlier developments in the field of organocatalytic activation of simple feedstock materials, providing potential ncAAs with diverse side chains, unique three-dimensional structures, and a high degree of functionality. These asymmetric organocatalytic strategies, useful for forging a wide range of C-C, C-H, and C-N bonds and/or combinations thereof, vary from classical name reactions, such as Ugi, Strecker, and Mannich reactions, to the most advanced concepts such as deracemisation, transamination, and carbene N-H insertion. Concurrently, we present some interesting mechanistic studies/models, providing information on the chirality transfer process. Finally, this perspective highlights, through the diversity of the amino acids (AAs) not selected by nature for protein incorporation, the most generic modes of activation, induction, and reactivity commonly used, such as chiral enamine, hydrogen bonding, Brønsted acids/bases, and phase-transfer organocatalysis, reflecting their increasingly important role in organic and applied chemistry.

Design, synthesis, and evaluation of novel arecoline-linked amino acid derivatives for insecticidal and antifungal activities

A series of arecoline derivatives with amino acid moieties were designed and synthesised using an acylamide condensation strategy, taking arecoline as the foundational structure. The insecticidal efficacy of these compounds against Aphis craccivora and Tetranychus cinnabarinus was evaluated. Notably, derivatives 3h and 3i demonstrated superior insecticidal activity compared with arecoline. Additionally, 3h and 3i showed good fungicidal effectiveness against two types of plant fungi. Moreover, molecular docking analyses suggested that 3h and 3i could affect the nervous systems of A. craccivora and T. cinnabarinus by binding to neuronal nicotinic acetylcholine receptors. These findings suggest that compounds 3h and 3i represent promising leads for further development in insecticide and fungicide research.

Ultrahigh Throughput Evolution of Tryptophan Synthase in Droplets via an Aptamer Sensor

Tryptophan synthase catalyzes the synthesis of a wide array of noncanonical amino acids and is an attractive target for directed evolution. Droplet microfluidics offers an ultrahigh throughput approach to directed evolution (up to 107 experiments per day), enabling the search for biocatalysts in wider regions of sequence space with reagent consumption minimized to the picoliter volume (per library member). While the majority of screening campaigns in this format on record relied on an optically active reaction product, a new assay is needed for tryptophan synthase. Tryptophan is not fluorogenic in the visible light spectrum and thus falls outside the scope of conventional droplet microfluidic readouts, which are incompatible with UV light detection at high throughput. Here, we engineer a tryptophan DNA aptamer into a sensor to quantitatively report on tryptophan production in droplets. The utility of the sensor was validated by identifying five-fold improved tryptophan synthases from ∼100,000 protein variants. More generally, this work establishes the use of DNA-aptamer sensors with a fluorogenic read-out in widening the scope of droplet microfluidic evolution.

Insights into Recent Nickel-Catalyzed Reductive and Redox C-C Coupling of Electrophiles, C(sp3)-H Bonds and Alkenes

ConspectusTransition metal-catalyzed reductive cross-coupling of two carbon electrophiles, also known as cross-electrophile coupling (XEC), has transformed the landscape of C-C coupling chemistry. Nickel catalysts, in particular, have demonstrated exceptional performance in facilitating XEC reactions, allowing for diverse elegant transformations by employing various electrophiles to forge C-C bonds. Nevertheless, several crucial challenges remain to be addressed. First, the intrinsic chemoselectivity between two structurally similar electrophiles in Ni-catalyzed C(sp3)-C(sp3) and C(sp2)-C(sp2) cross-coupling has not been well understood; this necessitates an excess of one of the coupling partners to achieve synthetically useful outcomes. Second, the substitution of economically and environmentally benign nonmetal reductants for Zn/Mn can help scale up XEC reactions and avoid trace metals in pharmaceutical products, but research in this direction has progressed slowly. Finally, it is highly warranted to leverage mechanistic insights from Ni-catalyzed XEC to develop innovative thermoredox coupling protocols, specifically designed to tackle challenges associated with difficult substrates such as C(sp3)-H bonds and unactivated alkenes.In this Account, we address the aforementioned issues by reviewing our recent work on the reductive coupling of C-X and C-O electrophiles, the thermoredox strategy for coupling associated with C(sp3)-H bonds and unactivated alkenes, and the use of diboron esters as nonmetal reductants to achieve reductive coupling. We focus on the mechanistic perspectives of the transformations, particularly how the key C-NiIII-C intermediates are generated, in order to explain the chemoselective and regioselective coupling results. The Account consists of four sections. First, we discuss the Zn/Mn-mediated chemoselective C(sp2)-C(sp2) and C(sp3)-C(sp3) bond formations based on the coupling of selected alkyl/aryl, allyl/benzyl, and other electrophiles. Second, we describe the use of diboron esters as versatile reductants to achieve C(sp3)-C(sp3) and C(sp3)-C(sp2) couplings, with an emphasis on the mechanistic consideration for the construction of C(sp3)-C(sp2) bonds. Third, we discuss leveraging C(sp3)-O bonds for effective C(sp3)-C bond formation via in situ halogenation of alcohols as well as the reductive preparation of α-vinylated and -arylated unusual amino esters. In the final section, we illustrate the thermoredox functionalization of challenging C(sp3)-H bonds with aryl and alkyl halides to afford C(sp3)-C bonds by taking advantage of the compatibility of Zn with the oxidant di-tert-butylperoxide (DTBP). Furthermore, we discuss a Ni-catalyzed and SiH/DTBP-mediated hydrodimerization of terminal alkenes to selectively forge head-to-head and methyl branched C(sp3)-C(sp3) bonds. This process, conducted in the presence or absence of catalytic CuBr2, provides a solution to a long-standing challenge: site-selective hydrocoupling of unactivated alkenes to produce challenging C(sp3)-C(sp3) bonds.

On-Resin Photochemical Decarboxylative Arylation of Peptides

Here we describe the application of photochemical decarboxylative arylation as a late-stage functionalization reaction for peptides. The reaction uses redox-active esters of aspartic acid and glutamic acid on the solid phase to provide analogues of aromatic amino acids. By using aryl bromides as arylation reagents, a wide variety of amino acids can be accessed without having to synthesize them individually in solution. The reaction is compatible with proteinogenic amino acids and was used to perform a structure-activity relationship study of a PRMT5 binding peptide.

Enantioselective Formal 1,2-Diamination of Ketenes with Iminosulfinamides: Asymmetric Synthesis of Unnatural α,α-Disubstituted α-Amino Acid Derivatives

A method was developed for the enantioselective formal 1,2-diamination of disubstituted ketenes using iminosulfinamides as nitrogen sources. The protocol involves the addition of lithium iminosulfinamides to ketenes to form N-iminosulfinyl amide metalloenolates. These metalloenolates then undergo a [2,3]-sigmatropic rearrangement to yield unnatural α,α-disubstituted α-amino acid derivatives with high enantiopurity. The chirality present at the sulfur atom in the iminosulfinamides is effectively transferred to α carbon of the resulting products, facilitating the highly enantioselective amination of ketenes.

Stereocontrolled Synthesis of Phosphoproline Analogues Containing a trans-Fused Octahydroindole Bicyclic System

Herein we report for the first time the diastereoselective synthesis of (2R,3aR,7aS)- and (2S,3aS,7aR)-octahydroindole-2-phosphonic acid (OicP trans-fused stereoisomers) from diethyl (R)- and (S)-phosphopyroglutamate derivative. The key steps of this procedure are the ruthenium tetroxide oxidation of enantiomerically pure diethyl (R)- and (S)-phosphoprolinate obtained through Katritzky's benzotriazole-oxazolidine methodology, a highly diastereoselective successive double 4,5-diallylation of diethyl (R)- and (S)-phosphopyroglutamate with allyl bromide and allyltrimethylsilane with a trans-addition mode, and a ring-closing metathesis with Grubbs' first-generation ruthenium catalyst.

Molecular and Structural Basis for Cγ-C Bond Formation by PLP-Dependent Enzyme Fub7

Pyridoxal 5'-phosphate (PLP)-dependent enzymes that catalyze γ-replacement reactions are prevalent, yet their utilization of carbon nucleophile substrates is rare. The recent discovery of two PLP-dependent enzymes, CndF and Fub7, has unveiled unique C-C bond forming capabilities, enabling the biocatalytic synthesis of alkyl- substituted pipecolic acids from O-acetyl-L-homoserine and β-keto acid or aldehyde derived enolates. This breakthrough presents fresh avenues for the biosynthesis of pipecolic acid derivatives. However, the catalytic mechanisms of these enzymes remain elusive, and a dearth of structural information hampers their extensive application. Here, we have broadened the catalytic scope of Fub7 by employing ketone-derived enolates as carbon nucleophiles, revealing Fub7's capacity for substrate-dependent regioselective α-alkylation of unsymmetrical ketones. Through an integrated approach combining X-ray crystallography, spectroscopy, mutagenesis, and computational docking studies, we offer a detailed mechanistic insight into Fub7 catalysis. Our findings elucidate the structural basis for its substrate specificity, stereoselectivity, and regioselectivity. Our work sets the stage ready for subsequent protein engineering effort aimed at expanding the synthetic utility of Fub7, potentially unlocking novel methods to access a broader array of noncanonical amino acids.

Copper-Catalyzed Asymmetric Remote C(sp3)-H Alkylation of N-Fluorocarboxamides with Glycine Derivatives and Peptides

Saturated hydrocarbon bonds are ubiquitous in organic molecules; to date, the selective functionalization of C(sp3)-H bonds continues to pose a notorious difficulty, thereby garnering significant attention from the synthetic chemistry community. During the past several decades, a wide array of powerful new methodologies has been developed to enantioselectively modify C(sp3)-H bonds that is successfully applied in asymmetric formation of diverse bonds, including C-C, C-N, and C-O bonds; nevertheless, the asymmetric C(sp3)-H alkylation is elusive and, therefore, far less explored. In this work, we report a direct and robust strategy to construct highly valuable enantioenriched unnatural α-amino acid (α-AA) cognates and peptides by a copper-catalyzed enantioselective remote C(sp3)-H alkylation of N-fluorocarboxamides and readily accessible glycine esters under ambient conditions. The key to success lies in the optically active Cu catalyst generated through the coordination of glycine derivatives to enantiopure bisphosphine/Cu(I) species, which is beneficial to the single electronic reduction of N-fluorocarboxamides and the subsequent stereodetermining alkylation. More importantly, all types (primary, secondary, tertiary, and even α-oxy) of δ-C(sp3)-H bonds could be site- and stereospecifically activated by the kinetically favored 1,5-hydrogen atom transfer (1,5-HAT) step.

Modular α-tertiary amino ester synthesis through cobalt-catalysed asymmetric aza-Barbier reaction

Unnatural chiral α-tertiary amino acids containing two different carbon-based substituents at the α-carbon centre are widespread in biologically active molecules. This sterically rigid scaffold is becoming a growing research interest in drug discovery. However, a robust protocol for chiral α-tertiary amino acid synthesis remains scarce due to the challenge of stereoselectively constructing sterically encumbered tetrasubstituted stereogenic carbon centres. Herein we report a cobalt-catalysed enantioselective aza-Barbier reaction of ketimines with various unactivated alkyl halides, including alkyl iodides, alkyl bromides and alkyl chlorides, enabling the formation of chiral α-tertiary amino esters with a high level of enantioselectivity and excellent functional group tolerance. Primary, secondary and tertiary organoelectrophiles are all tolerated in this asymmetric reductive addition protocol, which provides a complementary method for the well-exploited enantioselective nucleophilic addition with moisture- and air-sensitive organometallic reagents. Moreover, the three-component transformation of α-ketoester, amine and alkyl halide represents a formal asymmetric deoxygenative alkylamination of the carbonyl group.

Asymmetric Reductive Amination of α-Keto Acids Using Ir-Based Hydrogen Transfer Catalysts: An Access to Unprotected Unnatural α-Amino Acids

A direct asymmetric reductive amination of α-keto acids catalyzed by Cp*Ir complexes bearing a chiral N-(2-picolyl)sulfonamidato ligand is described. The combined use of optically active 2-phenyglycinol as an aminating agent is effective for the chemo- and stereoselective transfer hydrogenation using formic acid. The subsequent elimination of the hydroxyethyl moiety by orthoperiodic acid can afford various unprotected α-amino acids in satisfactory isolated yields (20 examples) with excellent optical purities (up to >99% ee).

Enzymatic Synthesis of Noncanonical α-Amino Acids Containing γ-Tertiary Alcohols

Noncanonical amino acids (ncAAs) containing tertiary alcohols are valuable as precursors of natural products and active pharmaceutical ingredients. However, the assembly of such ncAA scaffolds from simple material by C-C bond formation remains a challenging task due to the presence of multiple stereocenters and large steric hindrance. In this study, we present a novel solution to this problem through highly selective enzymatic decarboxylative aldol addition. This method allows for the streamlined assembly of multifunctionalized ncAAs with γ-tertiary alcohols from readily available materials, such as L -aspartatic acid and isatins, vicinal diones and keto esters. The modularity of electrophiles furnished four classes of ncAAs with decent efficiency as well as excellent site and stereocontrol. Computational modeling was employed to gain detailed insight into the catalytic mechanism and to provide a rationale for the observed selectivities. The method offers a single-step approach to producing multifunctionalized ncAAs, which can be directly utilized in peptide synthesis and bioactivity assessment.

Application of the LADA Strategy for the Synthesis of Unnatural Amino Acids through 1,2-Aryl Migration of Allylic Alcohols

Unnatural amino acids are versatile building blocks. Herein, we report the application of the LADA strategy for the direct synthesis of unnatural amino acids through 1,2-aryl migration of allylic alcohols. This reaction proceeds under mild conditions, tolerates diverse functionalities, and works smoothly on different thiols.

A rationally engineered small antimicrobial peptide with potent antibacterial activity

Antimicrobial resistance (AMR) is a silent pandemic declared by the WHO that requires urgent attention in the post-COVID world. AMR is a critical public health concern worldwide, potentially affecting people at different stages of life, including the veterinary and agriculture industries. Notably, very few new-age antimicrobial agents are in the current developmental pipeline. Thus, the design, discovery, and development of new antimicrobial agents are required to address the menace of AMR. Antimicrobial peptides (AMPs) are an important class of antimicrobial agents for combating AMR due to their broad-spectrum activity and ability to evade AMR through a multimodal mechanism of action. However, molecular size, aggregability, proteolytic degradation, cytotoxicity, and hemolysis activity significantly limit the clinical application of natural AMPs. The de novo design and engineering of a short synthetic amphipathic AMP (≤16 aa, Mol. Wt. ≤ 2 kDa) with an unusual architecture comprised of coded and noncoded amino acids (NCAAs) is presented here, which demonstrates potent antibacterial activity against a few selected bacterial strains mentioned in the WHO priority list. The designer AMP is conformationally ordered in solution and effectively permeabilizes the outer and inner membranes, leading to bacterial growth inhibition and death. Additionally, the peptide is resistant to proteolysis and has negligible cytotoxicity and hemolysis activity up to 150 μM toward cultured human cell lines and erythrocytes. The designer AMP is unique and appears to be a potent therapeutic candidate, which can be subsequently subjected to preclinical studies to explicitly understand and address the menace of AMR.

Preparing for the future of precision medicine: synthetic cell drug regulation

Synthetic cells are a novel class of cell-like bioreactors, offering the potential for unique advancements in synthetic biology and biomedicine. To realize the potential of those technologies, synthetic cell-based drugs need to go through the drug approval pipeline. Here, we discussed several regulatory challenges, both unique to synthetic cells, as well as challenges typical for any new biomedical technology. Overcoming those difficulties could bring transformative therapies to the market and will create a path to the development and approval of cutting-edge synthetic biology therapies. Graphical Abstract.

Straightforward Access to Free β2,3,3 -Amino Acids through One Pot C-H Activation/C-C Cleavage

The first synthesis of unnatural β2,3,3 -amino acids with a spirocyclic backbone by one-pot protocol has been presented. This reaction features wide functional group tolerance and feasibility of post-functionalization of natural products and biologically important molecules. Novel dipeptide and tripeptide structures were assembled using this newly developed β2,3,3 -amino acid in high efficiency. The combination of C-H activation and C-C cleavage for the synthesis of β-amino acids would trigger more promising synthetic routes for this compound.

One-pot chemoenzymatic syntheses of non-canonical amino acids

Despite their prevalent use in drug discovery and protein biochemistry, non-canonical amino acids are still challenging to synthesize through purely chemical means. In recent years, biocatalysis has emerged as a transformative paradigm for small-molecule synthesis. One strategy to further empower biocatalysis is to use it in combination with modern chemical reactions and take advantage of the strengths of each method to enable access to challenging structural motifs that were previously unattainable using each method alone. In this Mini-Review, we highlight several recent case studies that feature the synergistic use of chemical and enzymatic transformations in one pot to synthesize novel non-canonical amino acids.

ONE-SENTENCE SUMMARY

This Mini-Review highlights several recent case studies that feature the synergistic use of chemical and enzymatic transformations in one pot to synthesize novel non-canonical amino acids.

Expedient and divergent synthesis of unnatural peptides through cobalt-catalyzed diastereoselective umpolung hydrogenation

The development of a reliable method for asymmetric synthesis of unnatural peptides is highly desirable and particularly challenging. In this study, we present a versatile and efficient approach that uses cobalt-catalyzed diastereoselective umpolung hydrogenation to access noncanonical aryl alanine peptides. This protocol demonstrates good tolerance toward various functional groups, amino acid sequences, and peptide lengths. Moreover, the versatility of this reaction is illustrated by its successful application in the late-stage functionalization and formal synthesis of various representative chiral natural products and pharmaceutical scaffolds. This strategy eliminates the need for synthesizing chiral noncanonical aryl alanines before peptide formation, and the hydrogenation reaction does not result in racemization or epimerization. The underlying mechanism was extensively explored through deuterium labeling, control experiments, HRMS identification, and UV-Vis spectroscopy, which supported a reasonable CoI/CoIII catalytic cycle. Notably, acetic acid and methanol serve as safe and cost-effective hydrogen sources, while indium powder acts as the terminal electron source.

Rapid Analysis of Trace Amounts of Amino Acid Derivatives by a Formyl Group-Installed Crystalline Sponge

The Industries need techniques for the rapid structure analysis of amino acid derivatives. The amino acid derivatives are sometimes produced as impurities in the industrial production processes, and cause toxicity problems. Herein, we report the crystalline sponge (CS) method analysis of variety of amino acids using a formyl group installed CS crystal. Most amino acids possess a primary amino group, which can form Schiff-base with the formyl group under mild conditions. Thus, the formyl group installed CS crystal can efficiently capture the amino acids via Schiff-base formation. We successfully analyzed derivatives of 18 proteogenic amino acids, 6 non-proteogenic amino acids, and 4 dipeptides using the formyl group installed CS. We thus believe that the protocols shown in this study would serve the need of the industries.

ICH S7B In Vitro Assays Do Not Address Mechanisms of QTC Prolongation for Peptides and Proteins - Data in Support of Not Needing Dedicated QTC Studies

Current cardiac safety testing focuses on detecting drug-induced QTC prolongation as a surrogate for risk of Torsade de Pointes. The nonclinical strategy, described in International Conference on Harmonization (ICH) S7B, includes in vitro assessment of hERG block or ventricular repolarization delay and in vivo QT prolongation. Several studies have reported predictive values of ICH S7B results for clinical QTC outcomes for small molecules; none has examined peptides and proteins other than monoclonal antibodies. To address this knowledge gap, information for peptides and proteins submitted to the US Food and Drug Administration (FDA) was collected. Results of hERG assays, ventricular repolarization assays, and in vivo QT assessment were compared with clinical QTC study outcomes. The results show that 14% clinical QTC studies for approved and investigational products failed to exclude 10-ms QTC prolongation. Clinical QTC prolongation for these molecules lacked concentration-dependence which is expected for hERG block-mediated mechanism or QTC prolongation could not be excluded due to characterization in the clinical study. The hERG and ventricular repolarization assays do not identify clinical QTC prolongation potential for peptides and proteins. Lack of alignment between hERG and ventricular repolarization assay results and clinical QTC outcomes suggests that the mechanisms of QTC prolongation by some peptides and proteins are unrelated to direct cardiac ion channel block. Similar to large targeted proteins and monoclonal antibodies, peptides and proteins regardless of size have a low likelihood of direct cardiac ion channel interactions. This characteristic supports waiving the requirement for thorough QT assessment for products comprised of naturally occurring amino acids unless proarrhythmia potential is suggested by nonclinical or clinical data.

A synthetic route to artificial chiral α-amino acids featuring a 3,4-dihydroisoquinolone core through a Rh(III)-catalyzed functionalization of allyl groups in chiral Ni(II) complexes

Currently, non-proteinogenic α-amino acids (α-AAs) have attracted increasing interest in bio- and medicinal chemistry. In this context, the first protocol for the asymmetric synthesis of artificial α-AAs featuring a 3,4-dihydroisoquinolone core with two stereogenic centers was successfully elaborated. A straightforward Rh(III)-catalysed C-H activation/annulation reaction of various aryl hydroxamates with a set of robust and readily available chiral Ni(II) complexes, which have allylic appendages derived from glycine (Gly), alanine (Ala) and phenylalanine (Phe), allowed incorporation of a 3,4-dihydroisoquinolone scaffold into the chiral amino acid residue. The reaction was performed in methanol and under mild conditions (at room temperature under air atmosphere), providing separable diastereomeric complexes with up to 94% total yield. The target α-AA with a 3,4-dihydroisoquinolone core in an enantiopure form was subsequently released from the obtained chiral Ni(II) complexes via an acidic decomposition in aqueous HCl, along with the recovery of the chiral auxiliary ligand.

Sequence-based prediction of the intrinsic solubility of peptides containing non-natural amino acids

Non-natural amino acids are increasingly used as building blocks in the development of peptide-based drugs as they expand the available chemical space to tailor function, half-life and other key properties. However, while the chemical space of modified amino acids (mAAs) such as residues containing post-translational modifications (PTMs) is potentially vast, experimental methods for measuring the developability properties of mAA-containing peptides are expensive and time consuming. To facilitate developability programs through computational methods, we present CamSol-PTM, a method that enables the fast and reliable sequence-based prediction of the intrinsic solubility of mAA-containing peptides in aqueous solution at room temperature. From a computational screening of 50,000 mAA-containing variants of three peptides, we selected five different small-size mAAs for a total number of 37 peptide variants for experimental validation. We demonstrate the accuracy of the predictions by comparing the calculated and experimental solubility values. Our results indicate that the computational screening of mAA-containing peptides can extend by over four orders of magnitude the ability to explore the solubility chemical space of peptides and confirm that our method can accurately assess the solubility of peptides containing mAAs. This method is available as a web server at https://www-cohsoftware.ch.cam.ac.uk/index.php/camsolptm .

Electrochemical Synthesis of Unnatural Amino Acids via Anodic Decarboxylation of N-Acetylamino Malonic Acid Derivatives

Broad application of α,α-disubstituted cyclic amino acid derivatives in medicinal chemistry urges for analogue design with improved pharmacokinetic properties. Herein, we disclose an electrochemical approach toward unnatural THF- and THP-containing amino acid derivatives that relies on anodic decarboxylation-intramolecular etherification of inexpensive and readily available N-acetylamino malonic acid monoesters under Hofer-Moest reaction conditions. The decarboxylative cyclization proceeds under constant current conditions in an undivided cell in an aqueous medium without any added base. A successful bioisosteric replacement of the 1-aminocyclohexane-1-carboxylic acid subunit by the THP-containing amino acid scaffold in cathepsin K inhibitor balicatib helped to reduce lipophilicity while retaining low nanomolar enzyme inhibitory potency and comparable microsomal stability.

Dipeptides Containing Pyrene and Modified Photochemically Reactive Tyrosine: Noncovalent and Covalent Binding to Polynucleotides

Dipeptides 1 and 2 were synthesized from unnatural amino acids containing pyrene as a fluorescent label and polynucleotide binding unit, and modified tyrosine as a photochemically reactive unit. Photophysical properties of the peptides were investigated by steady-state and time-resolved fluorescence. Both peptides are fluorescent (Φf = 0.3-0.4) and do not show a tendency to form pyrene excimers in the concentration range < 10-5 M, which is important for their application in the fluorescent labeling of polynucleotides. Furthermore, both peptides are photochemically reactive and undergo deamination delivering quinone methides (QMs) (ΦR = 0.01-0.02), as indicated from the preparative photomethanolysis study of the corresponding N-Boc protected derivatives 7 and 8. Both peptides form stable complexes with polynucleotides (log Ka > 6) by noncovalent interactions and similar affinities, binding to minor grooves, preferably to the AT reach regions. Peptide 2 with a longer spacer between the fluorophore and the photo-activable unit undergoes a more efficient deamination reaction, based on the comparison with the N-Boc protected derivatives. Upon light excitation of the complex 2·oligoAT10, the photo-generation of QM initiates the alkylation, which results in the fluorescent labeling of the oligonucleotide. This study demonstrated, as a proof of principle, that small molecules can combine dual forms of fluorescent labeling of polynucleotides, whereby initial addition of the dye rapidly forms a reversible high-affinity noncovalent complex with ds-DNA/RNA, which can be, upon irradiation by light, converted to the irreversible (covalent) form. Such a dual labeling ability of a dye could have many applications in biomedicinal sciences.

Visible-light induced C(sp3)-H arylation of glycine derivatives by cerium catalysis

A Ce(III)-catalyzed, visible-light induced aerobic oxidative dehydrogenative coupling reaction between glycine derivatives and electron-rich arenes is disclosed. The protocol proceeds efficiently under mild conditions, providing an efficient method for the rapid synthesis of α-arylglycine derivatives without the need for an external photosensitizer and additional oxidant. Moreover, this protocol could be performed on a 5 mmol scale, without obvious reduction of the efficiency.

In silico identification of colchicine derivatives as novel and potential inhibitors based on molecular docking and dynamic simulations targeting multifactorial drug targets involved in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder, characterized by a gradual and steady deterioration in cognitive function over time. At least 50 million people worldwide are considered to have AD or another form of dementia. AD is marked by a gradual decline in cognitive abilities, memory deterioration and neurodegenerative transformations within the brain. The intricate and multifaceted nature of polygenic AD presents significant challenges within the landscape of drug development. The pathophysiology of AD unfolds in a non-linear and dynamic pattern, encompassing various systems and giving rise to a multitude of factors and hypotheses that contribute to the disease's onset. These encompass theories such as the beta-amyloid hypothesis, cholinergic hypothesis, tau hypothesis, oxidative stress and more. In the realm of drug development, polypharmacological drug profiles have emerged as a strategy that can yield combined or synergistic effects, effectively mitigating undesirable side effects and significantly enhancing the therapeutic efficacy of essential medications. With this concept in mind, our in-silico study sought to delve into the binding interactions of a diverse array of colchicine derivative compounds. These derivatives are chosen for their potential anti-inflammatory, antioxidant, anti-neurodegenerative and neuroprotective properties against Alzheimer's and other neurodegenerative diseases. We investigated compound interactions with AD-related targets, utilizing comprehensive molecular docking and dynamic simulations. COM111X showed impressive docking with acetylcholinesterase, indicating potential as an anti-Alzheimer's drug. COM112Y displayed strong docking scores with PDE4D and butyrylcholinesterase, suggesting dual inhibition for Alzheimer's treatment. Further in vitro and in vivo studies are warranted to explore these findings.Communicated by Ramaswamy H. Sarma.

Metal-free photoinduced C(sp3)-H/C(sp3)-H cross-coupling to access α‑tertiary amino acid derivatives

The cross-dehydrogenative coupling (CDC) reaction is the most direct and efficient method for constructing α-tertiary amino acids (ATAAs), which avoids the pre-activation of C(sp3)-H substrates. However, the use of transition metals and harsh reaction conditions are still significant challenges for these reactions that urgently require solutions. This paper presents a mild, metal-free CDC reaction for the construction of ATAAs, which is compatible with various benzyl C-H substrates, functionalized C-H substrates, and alkyl substrates, with good regioselectivity. Notably, our method exhibits excellent functional group tolerance and late-stage applicability. According to mechanistic studies, the one-step synthesized and bench-stable N-alkoxyphtalimide generates a highly electrophilic trifluoro ethoxy radical that serves as a key intermediate in the reaction process and acts as a hydrogen atom transfer reagent. Therefore, our metal-free and additive-free method offers a promising strategy for the synthesis of ATAAs under mild conditions.

Harnessing Aromatic-Histidine Interactions through Synergistic Backbone Extension and Side Chain Modification

Peptide engineering efforts have delivered drugs for diverse human diseases. Side chain alteration is among the most common approaches to designing new peptides for specific applications. The peptide backbone can be modified as well, but this strategy has received relatively little attention. Here we show that new and favorable contacts between a His side chain on a target protein and an aromatic side chain on a synthetic peptide ligand can be engineered by rational and coordinated side chain modification and backbone extension. Side chain modification alone was unsuccessful. Binding measurements, high-resolution structural studies and pharmacological outcomes all support the synergy between backbone and side chain modification in engineered ligands of the parathyroid hormone receptor-1, which is targeted by osteoporosis drugs. These results should motivate other structure-based designs featuring coordinated side chain modification and backbone extension to enhance the engagement of peptide ligands with target proteins.

Enzymatic Benzofuranoindoline Formation in the Biosynthesis of the Strained Bridgehead Bicyclic Dipeptide (+)-Azonazine A

We uncovered and reconstituted a concise biosynthetic pathway of the strained dipeptide (+)-azonazine A from marine-derived Aspergillus insulicola. Formation of the hexacyclic benzofuranoindoline ring system from cyclo-(l-Trp-N-methyl-l-Tyr) is catalyzed by a P450 enzyme through an oxidative cyclization. Supplementing the producing strain with various indole-substituted tryptophan derivatives resulted in the generation of a series of azonazine A analogs.

Copper catalyzed Shono-type oxidation of proline residues in peptide

Since the initial report in 1975, the Shono oxidation has become a powerful tool to functionalize the α position of amines, including proline derivatives, by electrochemical oxidation. However, the application of electrochemical Shono oxidations is restricted to the preparation of simple building blocks and homogeneous Shono-type oxidation of proline derivatives remains challenging. The late-stage functionalization at proline residues embedded within peptides is highly important as substitutions about the proline ring are known to affect biological and pharmacological activities. Here, we show that homogenous copper-catalyzed oxidation conditions complement the Shono oxidation and this general protocol can be applied to a series of formal C-C coupling reactions with a variety of nucleophiles using a one-pot procedure. This protocol shows good tolerance toward 19 proteinogenic amino acids and was used to functionalize several representative bioactive peptides, including captopril, enalapril, Smac, and endomorphin-2. Last, peptide cyclization can also be achieved by using an appropriately positioned side-chain hydroxyl moiety.

Tetrazole Diversification of Amino Acids and Peptides via Silver-Catalyzed Intermolecular Cycloaddition with Aryldiazonium Salts

Selective structural modification of amino acids and peptides is a central strategy in organic chemistry, chemical biology but also in pharmacology and material science. In this context, the formation of tetrazole rings, known to possess significant therapeutic properties, would expand the chemical space of unnatural amino acids but has received less attention. In this study, we demonstrated that the classic unimolecular Wolff rearrangement of α-amino acid-derived diazoketones could be replaced by a faster intermolecular cycloaddition reaction with aryldiazonium salts under identical practical conditions. This strategy provides an efficient synthetic platform that could transform proteinogenic α-amino acids into a plethora of unprecedented tetrazole-decorated amino acid derivatives with preservation of the stereocenters. Density functional theory studies shed some light on the reaction mechanism and provided information regarding the origins of the chemo- and regioselectivity. Furthermore, this diazo-cycloaddition protocol was applied to construct tetrazole-modified peptidomimetics and drug-like amino acid derivatives.

Engaging Isatins and Amino Acids in Multicomponent One-Pot 1,3-Dipolar Cycloaddition Reactions-Easy Access to Structural Diversity

Multicomponent reactions (MCRs) have undoubtedly emerged as the most indispensable tool for organic chemists worldwide, finding extensive utility in the synthesis of intricate natural products, heterocyclic molecules with significant bioactivity, and pharmaceutical agents. The multicomponent one-pot 1,3-dipolar cycloaddition reactions, which were initially conceptualized by Rolf Huisgen in 1960, find extensive application in contemporary heterocyclic chemistry. In terms of green synthesis, the multicomponent 1,3-dipolar cycloaddition is highly favored owing to its numerous advantages, including high step- and atom-economies, remarkable product diversity, as well as excellent efficiency and diastereoselectivity. Among the numerous pieces of research, the most fascinating reaction involves the utilization of azomethine ylides generated from isatins and amino acids that can be captured by various dipolarophiles. This approach offers a highly efficient and convenient method for constructing spiro-pyrrolidine oxindole scaffolds, which are crucial building blocks in biologically active molecules. Consequently, this review delves deeper into the dipolarophiles utilized in the 1,3-dipolar cycloaddition of isatins and amino acids over the past six years.

Multiplexed Assessment of Promiscuous Non-Canonical Amino Acid Synthase Activity in a Pyridoxal Phosphate-Dependent Protein Family

Pyridoxal phosphate (PLP)-dependent enzymes afford access to a variety of non-canonical amino acids (ncAAs), which are premier buildings blocks for the construction of complex bioactive molecules. The vinylglycine ketimine (VGK) subfamily of PLP-dependent enzymes plays a critical role in sulfur metabolism and is home to a growing set of secondary metabolic enzymes that synthesize γ-substituted ncAAs. Identification of VGK enzymes for biocatalysis faces a distinct challenge because the subfamily contains both desirable synthases as well as lyases that break down ncAAs. Some enzymes have both activities, which may contribute to pervasive mis-annotation. To navigate this complex functional landscape, we used a substrate multiplexed screening approach to rapidly measure the substrate promiscuity of 40 homologs in the VGK subfamily. We found that enzymes involved in transsulfuration are less likely to have promiscuous activities and often possess undesirable lyase activity. Enzymes from direct sulfuration and secondary metabolism generally had a high degree of substrate promiscuity. From this cohort, we identified an exemplary γ-synthase from Caldicellulosiruptor hydrothermalis (CahyGS). This enzyme is thermostable and has high expression (~400 mg protein per L culture), enabling preparative scale synthesis of thioether containing ncAAs. When assayed with l-allylglycine, CahyGS catalyzes a stereoselective γ-addition reaction to afford access to a unique set of γ-methyl branched ncAAs. We determined high-resolution crystal structures of this enzyme that define an open-close transition associated with ligand binding and set the stage for future engineering within this enzyme subfamily.

Metal-Free Late-Stage Alkylation of Tryptophan and Tryptophan-Containing Peptides with 1,3-Dithiane Derivatives

Late-stage diversification of structurally complex peptides has enormous potential for drug discovery and molecular imaging. We report a simple, metal-free, late-stage reductive C2 alkylation of tryptophan and tryptophan-containing peptides using readily available 1,3-dithianes. This alkylation protocol has a wide substrate scope and an excellent tolerance for reactive functional groups.

Synthesis of α,α-Diaryl-α-amino Acid Precursors by Reaction of Isocyanoacetate Esters with o-Quinone Diimides

A novel procedure for the synthesis of α,α-diaryl-α-amino acid derivatives has been developed. Silver oxide catalyzes the conjugate addition of α-aryl isocyanoacetates to o-quinone diimide, affording the corresponding α,α-diarylisocyano esters in excellent yields and regioselectivities in short reaction times. Acid hydrolysis of the isocyano group provides the corresponding amino acids bearing a diarylated tetrasubstituted carbon atom. The reaction is also amenable to the synthesis of α-alkyl-α-arylisocyano esters, while the reaction with 3-hydroxy o-quinone diimides provides 4H-benzo[e][1,3]oxazines via a conjugate addition/cyclization process.

Simplifying the Synthesis of Nonproteinogenic Amino Acids via Palladium-Catalyzed δ-Methyl C-H Olefination of Aliphatic Amines and Amino Acids

Transition metal-catalyzed directing group assisted C-H functionalizations provide a straightforward access to a wide variety of nonproteinogenic amino acids. While altering the side chain of an existing natural amino acids is one way, introducing a functional group to an aliphatic amine to synthesize versatile unnatural amino acids is another exciting avenue. In this work, we explore both the possibilities by the palladium-catalyzed δ-C(sp³)-H olefination of aliphatic amines and amino acids. A diverse substrate scope including sequential difunctionalizations followed by post synthetic transformations were achieved to understand the applicability of the current protocol. An in-depth mechanistic study was carried out to learn the mode of the reaction pathway.

Asymmetric Catalytic Friedel-Crafts Reactions of Unactivated Arenes

Since its discovery more than a century ago, the Friedel-Crafts reaction has manifested itself as a powerful method for the introduction of carbon substituents to arenes. Despite its potential generality, the scope of the reaction is intrinsically limited by the arene's nucleophilicity, which has previously restrained the applicability of asymmetric variants to activated substrates. To overcome this fundamental limitation, we report herein an asymmetric Friedel-Crafts reaction of unactivated, purely hydrocarbon arenes, alkoxybenzenes, and heteroarenes with N,O-acetals to give enantioenriched arylglycine esters. Highly regio- and stereoselective C-C bond formation was achieved using strong and confined Brønsted acid organocatalysts, enabling the first asymmetric catalytic Friedel-Crafts reaction of simple alkylbenzenes.

Lithio Tris(methylthio)methane as Hydroxy/Thio/Aminocarbonyl Anion Equivalent: Asymmetric Synthesis of α-Amino Acid Esters, Thioesters, Amides, and Peptides

The use of lithio tris(methylthio)methane as a hydroxy/thio/amino carbonyl anion equivalent in the synthesis of α-amino acids is reported. Addition of the reagent to nonracemic sulfinimines furnished the α-sulfinamido trithioformates in excellent diastereoselectivity. Unmasking the trithioformates to diverse functionalities, such as α-amino acid thioesters, esters, anilides, amides, and di/tri peptides, without epimerization of chiral centers was accomplished.

Stereoselective synthesis of S-norvaline and related amino acids through a common intermediate

A divergent, enantioselective synthetic strategy is reported to produce the non-proteinogenic, biologically active natural amino acids norvaline, 5-hydroxy-4-oxo-L-norvaline, and ɣ-oxonorvaline. These were synthesized in good yields (45-75%) from the common starting material (S)-allylglycine obtained by asymmetric transfer allylation of glycine Schiff base using the Corey catalyst derived from cinchonidine in more than 97% enantiomeric excess.

Inhibitory Potential of Synthetic Amino Acid Derivatives against Digestive Enzymes as Promising Hypoglycemic and Anti-Obesity Agents

Over the last decades, the increased incidence of metabolic disorders, such as type two diabetes and obesity, has motivated researchers to investigate new enzyme inhibitors. In this study, the inhibitory effects of synthetic amino acid derivatives (PPC80, PPC82, PPC84, PPC89, and PPC101) on the activity of digestive enzymes were assessed using in vitro assays. The inhibitory effect was determined by the inhibition percentage and the 50% inhibitory concentration (IC₅₀), and the mechanism of action was investigated using kinetic parameters and Lineweaver-Burk plots. PPC80, PPC82, and PPC84 inhibited pancreatic lipase (IC₅₀ of 167-1023 µM) via competitive or mixed mechanisms. The activity of pancreatic α-amylase was suppressed by PPC80, PPC82, PPC84, PPC89, and PPC101 (IC₅₀ of 162-519 µM), which acted as competitive or mixed inhibitors. Finally, PPC84, PPC89, and PPC101 also showed potent inhibitory effects on α-glucosidase (IC₅₀ of 51-353 µM) as competitive inhibitors. The results suggest that these synthetic amino acid derivatives have inhibitory potential against digestive enzymes and may be used as therapeutic agents to control metabolic disorders.

Copper-catalyzed asymmetric C(sp3)-H cyanoalkylation of glycine derivatives and peptides

Alkylnitriles play important roles in many fields because of their unique electronic properties and structural characteristics. Incorporating cyanoalkyl with characteristic spectroscopy and reactivity properties into amino acids and peptides is of special interest for potential imaging and therapeutic purposes. Here, we report a copper-catalyzed asymmetric cyanoalkylation of C(sp³)-H. In the reactions, glycine derivatives can effectively couple with various cycloalkanone oxime esters with high enantioselectivities, and the reaction can be applied to the late-stage modification of peptides with good yields and excellent stereoselectivities, which is useful for modern peptide synthesis and drug discovery. The mechanistic studies show that the in situ formed copper complex by the coordination of glycine derivatives and chiral phosphine Cu catalyst can not only mediate the single electronic reduction of cycloalkanone oxime ester but also control the stereoselectivity of the cyanoalkylation reaction.

Targeting Peptides: The New Generation of Targeted Drug Delivery Systems

Peptides can act as targeting molecules, analogously to oligonucleotide aptamers and antibodies. They are particularly efficient in terms of production and stability in physiological environments; in recent years, they have been increasingly studied as targeting agents for several diseases, from tumors to central nervous system disorders, also thanks to the ability of some of them to cross the blood-brain barrier. In this review, we will describe the techniques employed for their experimental and in silico design, as well as their possible applications. We will also discuss advancements in their formulation and chemical modifications that make them even more stable and effective. Finally, we will discuss how their use could effectively help to overcome various physiological problems and improve existing treatments.

Enantioselective β-Selective Addition of Isoxazolidin-5-ones to Allenoates Catalyzed by Quaternary Ammonium Salts

The enantioselective addition of isoxazolidin-5-ones to the β-carbon of allenoates has been carried out by using a novel spirobiindane-based quaternary ammonium salt catalyst. This protocol, which proceeds under classical liquid-solid phase-transfer conditions, gives access to unprecedented highly functionalized β2,2-amino acid derivatives with good enantioselectivities and in high yields, and further manipulations of these products have been carried out as well.

Beyond 20 in the 21st Century: Prospects and Challenges of Non-canonical Amino Acids in Peptide Drug Discovery

Life is constructed primarily using a toolbox of 20 canonical amino acids-relying upon these building blocks for the assembly of proteins and peptides that regulate nearly every cellular task, including cell structure, function, and maintenance. While Nature continues to be a source of inspiration for drug discovery, medicinal chemists are not beholden to only 20 canonical amino acids and have begun to explore non-canonical amino acids (ncAAs) for the construction of designer peptides with improved drug-like properties. However, as our toolbox of ncAAs expands, drug hunters are encountering new challenges in approaching the iterative peptide design-make-test-analyze cycle with a seemingly boundless set of building blocks. This Microperspective focuses on new technologies that are accelerating ncAA interrogation in peptide drug discovery (including HELM notation, late-stage functionalization, and biocatalysis) while shedding light on areas where further investment could not only accelerate the discovery of new medicines but also improve downstream development.