Comprehensive Structure-Activity Relationship Studies of Cepafungin Enabled by Biocatalytic C-H Oxidations

Enantioselective total synthesis of lycoposerramine congeners through late-stage nitrogen deletion

Lycopodium alkaloids are attractive synthetic targets due to their diverse and unusual skeletal features. While numerous synthetic approaches have been reported, there still remain outstanding synthetic challenges to several lycopodium alkaloids. Herein, a concise total synthesis of lycoposerramine congeners is accomplished through the use of nitrogen deletion strategy (N-deletion) to combine two fully elaborated piperidine and tetrahydroquinoline fragments. Specifically, two natural congeners, lycoposerramine V and W, previously accessible only in 18-23 steps, are each synthesized in 10 steps or less. In contrast to the successful use of N-deletion, many C-C bond forming reactions surveyed fail to deliver the desired coupling product. To further highlight its modular nature, the strategy is applied in the synthesis of two unnatural epimers of lycoposerramine V and W. This work demonstrates the benefits of incorporating modern synthetic methodologies in streamlining access to complex molecules.

Sequential oxidation of L-lysine by a non-heme iron hydroxylase

2-oxoglutarate-dependent non-heme iron hydroxylases offer a direct route to functionalizing C(sp3)-H bonds across a diverse range of substrates, making them prime candidates for chemoenzymatic synthetic strategies. We demonstrate the ability of a non-heme iron L-lysine dioxygenase to perform sequential oxidation and computationally explore structural elements that promote this reactivity.

Biocatalytic C-H oxidation meets radical cross-coupling: Simplifying complex piperidine synthesis

Modern medicinal chemists are targeting more complex molecules to address challenging biological targets, which leads to synthesizing structures with higher sp3 character (Fsp3) to enhance specificity as well as physiochemical properties. Although traditional flat, high-fraction sp2 molecules, such as pyridine, can be decorated through electrophilic aromatic substitution and palladium (Pd)-based cross-couplings, general strategies to derivatize three-dimensional (3D) saturated molecules are far less developed. In this work, we present an approach for the rapid, modular, enantiospecific, and diastereoselective functionalization of piperidine (saturated analog of pyridine), combining robust biocatalytic carbon-hydrogen oxidation with radical cross-coupling. This combination is directly analogous to electrophilic aromatic substitution followed by Pd-couplings for flat molecules, streamlining synthesis of 3D molecules. This study offers a generalizable strategy for accessing complex architectures, appealing to both medicinal and process chemists.

Biocatalytic Amino Acid Functionalisation

The success of new therapeutic modalities relies on advancements in synthetic chemistry to produce compounds for evaluation throughout the drug discovery process. The use of non-canonical amino acids (ncAAs) allows the properties of peptide drugs to be modified and optimised beyond the defined characteristics of the 20 proteogenic amino acids. Synthesis of ncAAs can be either through a bespoke chemical synthesis, or directly from the parent compound - using either traditional chemical reagents or using enzymes - to achieve the desired modification. This review will highlight recent advancements in the enzymatic functionalisation of amino acids to produce a variety of ncAAs.

Advances, opportunities, and challenges in methods for interrogating the structure activity relationships of natural products

Time span in literature: 1985-early 2024Natural products play a key role in drug discovery, both as a direct source of drugs and as a starting point for the development of synthetic compounds. Most natural products are not suitable to be used as drugs without further modification due to insufficient activity or poor pharmacokinetic properties. Choosing what modifications to make requires an understanding of the compound's structure-activity relationships. Use of structure-activity relationships is commonplace and essential in medicinal chemistry campaigns applied to human-designed synthetic compounds. Structure-activity relationships have also been used to improve the properties of natural products, but several challenges still limit these efforts. Here, we review methods for studying the structure-activity relationships of natural products and their limitations. Specifically, we will discuss how synthesis, including total synthesis, late-stage derivatization, chemoenzymatic synthetic pathways, and engineering and genome mining of biosynthetic pathways can be used to produce natural product analogs and discuss the challenges of each of these approaches. Finally, we will discuss computational methods including machine learning methods for analyzing the relationship between biosynthetic genes and product activity, computer aided drug design techniques, and interpretable artificial intelligence approaches towards elucidating structure-activity relationships from models trained to predict bioactivity from chemical structure. Our focus will be on these latter topics as their applications for natural products have not been extensively reviewed. We suggest that these methods are all complementary to each other, and that only collaborative efforts using a combination of these techniques will result in a full understanding of the structure-activity relationships of natural products.

Engineering Hydroxylase Activity, Selectivity, and Stability for a Scalable Concise Synthesis of a Key Intermediate to Belzutifan

Biocatalytic oxidations are an emerging technology for selective C-H bond activation. While promising for a range of selective oxidations, practical use of enzymes catalyzing aerobic hydroxylation is presently limited by their substrate scope and stability under industrially relevant conditions. Here, we report the engineering and practical application of a non-heme iron and α-ketoglutarate-dependent dioxygenase for the direct stereo- and regio-selective hydroxylation of a non-native fluoroindanone en route to the oncology treatment belzutifan, replacing a five-step chemical synthesis with a direct enantioselective hydroxylation. Mechanistic studies indicated that formation of the desired product was limited by enzyme stability and product overoxidation, with these properties subsequently improved by directed evolution, yielding a biocatalyst capable of >15,000 total turnovers. Highlighting the industrial utility of this biocatalyst, the high-yielding, green, and efficient oxidation was demonstrated at kilogram scale for the synthesis of belzutifan.

Optical Control of Proteasomal Protein Degradation with a Photoswitchable Lipopeptide

Photolipids have emerged as attractive tools for the optical control of lipid functions. They often contain an azobenzene photoswitch that imparts a cis double-bond upon irradiation. Herein, we present the application of photoswitching to a lipidated natural product, the potent proteasome inhibitor cepafungin I. Several azobenzene-containing lipids were attached to the cyclopeptide core, yielding photoswitchable derivatives. Most notably, PhotoCep4 exhibited a 10-fold higher cellular potency in its light-induced cis-form, matching the potency of natural cepafungin I. The length of the photolipid tail and distal positioning of the azobenzene photoswitch with respect to the macrocycle is critical for this activity. In a proteome-wide experiment, light-triggered PhotoCep4 modulation showed high overlap with constitutively active cepafungin I. The mode of action was studied using crystallography and revealed an identical binding of the cyclopeptide in comparison to cepafungin I, suggesting that differences in their cellular activity originate from switching the tail structure. The photopharmacological approach described herein could be applicable to many other natural products as lipid conjugation is common and often necessary for potent activity. Such lipids are often introduced late in synthetic routes, enabling facile chemical modifications.

Non-Native Site-Selective Enzyme Catalysis

The ability to site-selectively modify equivalent functional groups in a molecule has the potential to streamline syntheses and increase product yields by lowering step counts. Enzymes catalyze site-selective transformations throughout primary and secondary metabolism, but leveraging this capability for non-native substrates and reactions requires a detailed understanding of the potential and limitations of enzyme catalysis and how these bounds can be extended by protein engineering. In this review, we discuss representative examples of site-selective enzyme catalysis involving functional group manipulation and C-H bond functionalization. We include illustrative examples of native catalysis, but our focus is on cases involving non-native substrates and reactions often using engineered enzymes. We then discuss the use of these enzymes for chemoenzymatic transformations and target-oriented synthesis and conclude with a survey of tools and techniques that could expand the scope of non-native site-selective enzyme catalysis.