Enantiomerically pure alpha-amino acid synthesis via hydroboration-suzuki cross-coupling

Stereoselective Synthesis of meso- and l,l-Diaminopimelic Acids from Enone-Derived α-Amino Acids

The stereoselective synthesis of meso-diaminopimelic acid (meso-DAP), the key cross-linking amino acid of the peptidoglycan cell wall layer in Gram-negative bacteria, and its biological precursor, l,l-DAP, is described. The key step involved stereoselective reduction of a common enone-derived amino acid by substrate- or reagent-based control. Overman rearrangement of the resulting allylic alcohols, concurrent alkene hydrogenation and trichloroacetamide reduction, and subsequent ruthenium-catalyzed arene oxidation completed the synthesis of each stereoisomer. The synthetic utility of this approach was demonstrated with the efficient preparation of an l,l-DAP-derived dipeptide.

Nucleophilic Addition of Amides to Haloalkynes: Synthesis of (Z)-β-Halovinyl Amides as Dual Precursors of Alkylidene Carbenes and Allyl Halides

Toward a regioselective method for the synthesis of β-halovinyl amides, we developed a transition-metal-free nucleophilic addition reaction of amides to haloalkynes. The regioselective nucleophilic addition was achieved under solvent-free conditions using phosphonates to protonate the intermediate alkylidene carbenoids, thus suppressing their decomposition. Furthermore, we demonstrate that β-halovinyl amides can serve as dual precursors of allyl halides and alkylidene carbenes to obtain functionalized indoles and pyrrolidones.

Synthesis and applications of symmetric amino acid derivatives

Symmetric α-amino acid derivatives can be used for the synthesis of intermolecularly linked peptides such as dimer-type peptides, and modified peptides in which two amino acids are intramolecularly linked. They are also synthetic intermediates for the total synthesis of natural products and functional molecules. These symmetric amino acid derivatives must be prepared based on organic synthesis. It is necessary to develop an optimal synthetic strategy for constructing the target symmetric amino acid derivative. In this review, we will introduce strategies for synthesizing symmetric amino acid derivatives. Additionally, selected applications of these amino acids in the life sciences will be described.

Umpolung Ala B Reagents for the Synthesis of Non‐Proteogenic Amino Acids, Peptides and Proteins**

Non-proteogenic amino acids and functionalized peptides are important motifs in modern drug discovery. Here we report that Ala^B can serve as universal building blocks in the synthesis of a diverse collection of modified amino acids, peptides, and proteins. First, we develop the synthesis of Ala^B from redox-active esters of aspartic acid resulting in a series of β-boronoalanine derivatives. Next, we show that Ala^B can be integrated into automated oligopeptide solid-phase synthesis. Ala^B is compatible with common transformations used in preparative peptide chemistry such as native chemical ligation and radical desulfurization as showcased by total synthesis of Ala^B -containing ubiquitin. Furthermore, Ala^B reagents participate in Pd-catalyzed reactions, including C-C cross-couplings and macrocyclizations. Taken together, Ala^B synthons are practical reagents to access modified peptides, proteins, and in the synthesis of cyclic/stapled peptides.

Radical 1,4-Aryl Migration Enabled Remote Cross-Electrophile Coupling of α-Amino-β-Bromo Acid Esters with Aryl Bromides

We report an unprecedented, efficient nickel-catalysed radical relay for the remote cross-electrophile coupling of β-bromo-α-benzylamino acid esters with aryl bromides via 1,4-aryl migration/arylation cascades. β-Bromo-α-benzylamino acid esters are considered as unique molecular scaffolds allowing for aryl migration reactions, which are conceptually novel variants for the radical Truce-Smiles rearrangement. This reaction enables the formation of two new C(sp³ )-C(sp² ) bonds using a bench-stable Ni/bipyridine/Zn system featuring a broad substrate scope and excellent diastereoselectivity, which provides an effective platform for the remote aryl group migration and arylation of amino acid esters via redox-neutral C(sp³ )-C(sp² ) bond cleavage. Mechanistically, this cascade reaction is accomplished by combining two powerful catalytic cycles consisting of a cross-electrophile coupling and radical 1,4-aryl migration through the generation of C(sp³ )-centred radical intermediates from the homolysis of C(sp³ )-Br bonds and the switching of the transient alkyl radical into a robust α-aminoalkyl radical.

Organometallic AlaM Reagents for Umpolung Peptide Diversification

Selective modifications of peptides and proteins have emerged as a promising strategy to develop novel mechanistic probes and prepare compounds with translational potentials. Here, we report alanine carbastannatranes AlaSn as a universal synthon in various C-C and C-heteroatom bond-forming reactions. These reagents are compatible with peptide manipulation techniques and can undergo chemoselective conjugation in minutes when promoted by Pd(0). Despite their increased nucleophilicity and propensity to transfer the alkyl group, C(sp3)-C(sp2) coupling with AlaSn can be accomplished at room temperature under buffered conditions (pH 6.5-8.5). We also show that AlaSn can be easily transformed into several canonical L- and D-amino acids in arylation, acylation, and etherification reactions. Furthermore, AlaSn can partake in macrocyclizations exemplified by the synthesis of medium size cyclic peptides with various topologies. Taken together, metalated alanine AlaSn demonstrates unparalleled scope and represents a new type of umpolung reagents suitable for structure-activity relationship studies and peptide diversification.

Recent Progress Towards Synthesis of the Indolizidine Alkaloid 195B

Background:

Natural products have been received attention due to their importance in human life as those are biologically active. In this review, there are some reports through different methods related to the synthesis of the indolizidine 195B which was extracted from poisonous frog; however, due to respect nature, the synthesis of natural compounds such as indolizidine has been attracted much attention among scientists and researchers.

Objective:

This review discloses the procedures and methods to provide indolizidine 195B from 1989 to 2018 due to their importance as a natural product.

Conclusion:

There are several methods to give rise to the indolizidine 195B as a natural product that is highly active from the biological perspective in pharmaceutical chemistry. In summary, many protocols for the preparations of indolizidine 195B from various substrates, several reagents, and conditions have been reported from different aromatic and aliphatic.

Recent Progress Towards Synthesis of the Indolizidine Alkaloid 195B

Background:

Natural products have been received attention due to their importance in human life as those are biologically active. In this review, there are some reports through different methods related to the synthesis of the indolizidine 195B which was extracted from poisonous frog; however, due to respect nature, the synthesis of natural compounds such as indolizidine has been attracted much attention among scientists and researchers.

Objective:

This review discloses the procedures and methods to provide indolizidine 195B from 1989 to 2018 due to their importance as a natural product.

Conclusion:

There are several methods to give rise to the indolizidine 195B as a natural product that is highly active from the biological perspective in pharmaceutical chemistry. In summary, many protocols for the preparations of indolizidine 195B from various substrates, several reagents, and conditions have been reported from different aromatic and aliphatic.

Catalytic Asymmetric Hydrogenation of Dehydroamino Acid Esters with Biscarbamate Protection and Its Application to the Synthesis of xCT Inhibitors

Catalytic asymmetric hydrogenation of dehydroamino acid esters with biscarbamate protection was examined for the first time to prepare optically active amino acids. The new method was successfully applied to the synthesis of new cystine-glutamate exchanger inhibitors.

Synthesis and Applications of (ONO Pincer)Ruthenium-Complex-Bound Norvalines

Two (ONO pincer)ruthenium-complex-bound norvalines, Boc-[Ru(pydc)(terpy)]Nva-OMe (1; Boc=tert-butyloxycarbonyl, terpy=terpyridyl, Nva=norvaline) and Boc-[Ru(pydc)(tBu-terpy)]Nva-OMe (5), were successfully synthesized and their molecular structures and absolute configurations were unequivocally determined by single-crystal X-ray diffraction. The robustness of the pincer Ru complexes and norvaline scaffolds against acidic/basic, oxidizing, and high-temperature conditions enabled us to perform selective transformations of the N-Boc and C-OMe termini into various functional groups, such as alkyl amide, alkyl urea, and polyether groups, without the loss of the Ru center or enantiomeric purity. The resulting dialkylated Ru-bound norvaline, n-C11 H23 CO-l-[Ru(pydc)(terpy)]Nva-NH-n-C11 H23 (l-4) was found to have excellent self-assembly properties in organic solvents, thereby affording the corresponding supramolecular gels. Ru-bound norvaline l-1 exhibited a higher catalytic activity for the oxidation of alcohols by H2 O2 than parent complex [Ru(pydc)(terpy)] (11 a).

Expeditious synthesis of enantiopure, orthogonally protected bis-α-amino acids (OPBAAs) and their use in a study of Nod1 stimulation

A convenient approach towards the synthesis of orthogonally protected chiral bis-α-amino acids (OPBAAs) is described. The key transformations include: (1) a highly stereoselective conjugation (alkylation) of the Schöllkopf bis-lactim ethers and oxazolidinyl alkyl halides to build a backbone skeleton; and (2) our orthogonal protection strategy. A series of enantiopure OPBAAs bearing a variety of alkyl chain as a spacer; two stereogenic centers; and three protecting groups were prepared as examples. These versatile molecules were applied to the synthesis of biologically interesting di- or tri-peptide analogues, including chiral iE-meso-DAP and A-iE-meso-DAP, for the study of Nod1 activation in the innate immune response.

Crystal structure of N-(tert-but-oxy-carbon-yl)glycyl-(Z)-β-bromo-dehydro-alanine methyl ester [Boc-Gly-(β-Br)((Z))ΔAla-OMe]

The title compound, C11H17BrN2O5, is a de-hydro-amino acid with a C=C bond between the α- and β-C atoms. The amino acid residues are linked trans to each other and there are no strong intra-molecular hydrogen bonds. The torsion angles indicate a non-helical conformation of the mol-ecule. The dipeptide folding is influenced by an inter-molecular N-H⋯O hydrogen bond and also minimizes steric repulsion. In the crystal, mol-ecules are linked by strong N-H⋯O hydrogen bonds, generating (001) sheets. The sheets are linked by weak C-H⋯O and C-H⋯Br bonds and short Br⋯Br [3.4149 (3) Å] inter-actions.

Chemical structure, biosynthesis and synthesis of free and glycosylated pyridinolines formed by cross-link of bone and synovium collagen

This review focuses on the chemical structure, biosynthesis and synthesis of free and glycosylated pyridinolines (Pyds), fluorescent collagen cross-links, with a pyridinium salt structure. Pyds derive from the degradation of bone collagen and have attracted attention for their use as biochemical markers of bone resorption and to assess fracture risk prediction in persons suffering from osteoporosis, bone cancer and other bone or collagen diseases. We consider and critically discuss all reported syntheses of free and glycosylated Pyds evidencing an unrevised chemistry, original and of general utility, analysis of which allows us to also support a previously suggested non-enzymatic formation of Pyds in collagen better rationalizing and justifying the chemical events.

A facile synthesis of fully protected meso-diaminopimelic acid (DAP) and its application to the preparation of lipophilic N-acyl iE-DAP

Synthesis of beneficial protected meso-DAP 9 by cross metathesis of the Garner aldehyde-derived vinyl glycine 1b with protected allyl glycine 2 in the presence of Grubbs second-generation catalyst was performed. Preparation of lipophilic N-acyl iE-DAP as potent agonists of NOD 1-mediated immune response from 9 is described.

Stereoselective synthesis of unsaturated and functionalized L-NHBoc amino acids, using Wittig reaction under mild phase-transfer conditions

The stereoselective synthesis of a new amino acid phosphonium salt was described by quaternization of melting triphenylphosphine with the γ-iodo NHBoc-amino ester, derived from L-aspartic acid. The deprotection of the carboxylic acid function to afford the phosphonium salt with a free carboxylic acid group was achieved by a palladium-catalyzed desallylation reaction. This phosphonium salt was used in the Wittig reaction with aromatic or aliphatic aldehydes and trifluoroacetophenone, under solid-liquid phase-transfer conditions in chlorobenzene and in the presence of K(3)PO(4) as weak base, to afford the corresponding unsaturated amino acids without racemization. Thus, the reaction with substituted aldehydes allows to graft various functionalized groups on the lateral chain of the amino acid, such as trifluoromethyl, cyano, nitro, ferrocenyl, boronato, or azido. In addition, the reaction of the amino acid Wittig reagent with α,β-unsaturated aldehydes leads to amino acids bearing a diene on the lateral chain. Finally, this amino acid phosphonium salt appears to be a new powerful tool for the preparation of unsaturated and non-proteinogenic α-amino acids, directly usable for the synthesis of customized peptides.

Peptidoglycan as Nod1 ligand; fragment structures in the environment, chemical synthesis, and their innate immunostimulation

Covering: up to 2011. This review focuses on the recent revealing of the immunostimulatory bacterial cell wall peptidoglycan (PGN) fragments as Nod1 ligands, especially a newly developed chemical synthesis of the partial structures, fragment structures in the environment and bacterial supernatant, and the immunostimulatory activities of the Nod1 ligands.

Sequential allylic C-H amination/vinylic C-H arylation: a strategy for unnatural amino acid synthesis from α-olefins

Tandem reaction sequences that selectively convert multiple C-H bonds of abundant hydrocarbon feedstocks to functionalized materials enable rapid buildup of molecular complexity in an economical way. A tandem C-H amination/vinylic C-H arylation reaction sequence is described under Pd(II)/sulfoxide-catalysis that furnishes a wide range of α- and β-homophenylalanine precursors from commodity α-olefins and readily available aryl boronic acids. General routes to enantiopure amino acid esters and densely functionalized homophenylalanine derivatives are demonstrated.

Structures, synthesis, and human Nod1 stimulation of immunostimulatory bacterial peptidoglycan fragments in the environment

Bacteria release immunostimulatory compounds to the environment, and one of the stimulants is the ligand of nucleotide-binding oligomerization domain protein 1 (Nod1), an intracellular protein involved in the recognition of the bacterial component peptidoglycans having a diaminopimelic acid (DAP) structure. The polymorphisms of Nod1 have been linked to several inflammatory diseases and allergies that are strongly affected by environmental factors. The present paper summarizes recent results on the isolation and structural elucidation of natural human Nod1 (hNod1) ligands from the Escherichia coli (E. coli) K-12 culture supernatant, the first chemical synthesis of these natural ligands and related PGN fragments structures, and the hNod1 stimulatory activities of the chemically synthesized DAP-type PGN fragments. For structural characterization studies, the 7-(diethylamino)coumarin-3-carbonyl (DEAC) labeling method was also used to enhance the sensitivity in mass spectrometry studies, in order to observe PGN fragments in a comprehensive manner. The results suggest that DAP-containing bacteria release certain hNod1 ligands to the environment and that these ligands accumulate in the environment and regulate the immune system through Nod1.

Synthesis of diaminopimelic acid containing peptidoglycan fragments and tracheal cytotoxin (TCT) and investigation of their biological functions

Bacterial cell wall peptidoglycan (PGN) is a potent immunostimulator and immune adjuvant. The PGN of Gram-negative bacteria and some Gram-positive bacteria contain meso-diaminopimelic acid (meso-DAP), and we have recently shown that the intracellular protein Nod1 is a PGN receptor and recognizes DAP-containing peptides. In this study, we achieved the synthesis of DAP-containing PGN fragments, including the first chemical synthesis of tracheal cytotoxin (TCT), GlcNAc-(beta1-4)-(anhydro)MurNAc-L-Ala-gamma-D-Glu-meso-DAP-D-Ala, and a repeating-unit of DAP-type PGN, GlcNAc-(beta1-4)-MurNAc-L-Ala-gamma-D-Glu-meso-DAP-D-Ala. For the synthesis of PGN fragments, we first established a new synthetic method for an orthogonally protected meso-DAP derivative, and then we constructed the glycopeptide structures. The ability of these fragments to stimulate human Nod1, as well as differences in Nod1 recognition of the variety of synthesized ligand structures were examined. The results showed that the substitution of the N terminus of iE-DAP is necessary for stronger Nod1 recognition, but the structure of the substituent seems not to be strictly recognized. The importance of the carboxyl group at the 2-position of DAP for human Nod1 stimulation was also shown.

Synthesis of unsymmetrical biphenyls as potent cytotoxic agents

Twenty-six unsymmetrical biphenyls were synthesized and evaluated for cytotoxic activity against DU145, A549, KB and KB-Vin tumor cell lines. Three compounds 27, 35 and 40 showed very potent activity against the HTCL panel with an IC(50) value range of 0.04-3.23 microM. In addition, fourteen active compounds were all more potent against the drug-resistant KB-Vin cell line than the parental KB cell line. Preliminary SAR analysis indicated that two bulky substituents on the 2,2'-positions of unsymmetrical biphenyl skeleton are necessary and crucial for in vitro anticancer activity, thus providing a good starting point to develop unsymmetrical biphenyls as novel anticancer agents.

Synthesis, conformational analysis, and biological evaluation of 1-hexylindolactam-V10 as a selective activator for novel protein kinase C isozymes

Conventional and novel protein kinase C (PKC) isozymes are the main targets of tumor promoters. We developed 1-hexylindolactam-V10 ( 5) as a selective activator for novel PKC isozymes that play important roles in various cellular processes related to tumor promotion, ischemia--reperfusion injury in the heart, and Alzheimer's disease. The compound existed as a mixture of three conformers. The trans-amide restricted analogues of 5 ( 14 and 15) hardly bound to PKC isozymes, suggesting that the active conformation of 5 could be that with a cis-amide. Compound 5 selectively translocated novel PKC isozymes over conventional PKC isozymes in HeLa cells at 0.1-1 microM. These results suggest that 5 could be useful for the functional analysis of novel PKC isozymes.

Synthesis and solution conformation studies of 3-substituted uridine and pseudouridine derivatives

A series of 3-substituted uridine and pseudouridine derivatives, based on the naturally occurring 3-(3-amino-3-carboxypropyl) modification, were synthesized. Their aqueous solution conformations were determined by using circular dichroism and NMR spectroscopy. Functional group composition and chain length were shown to have only a subtle influence on the distribution of syn/anti conformations of the modified nucleosides. The dominating factor appears to be the glycosidic linkage (C- vs. N-glycoside) in determining the nucleoside conformation.