Heteroatom-substitution as a strategy for increasing the potency of competitive NMDA antagonists

An efficient synthesis of cis-4-hydroxyphosphonic and cis-4-hydroxyphosphinic analogs of pipecolic acid from cyclic enaminones

An expedient synthetic entry to cis-4-hydroxyphosphonic and cis-4-hydroxyphosphinic analogs of cis-4-hydroxypipecolic acid is presented in this paper. The main feature of this methodology is the highly regioselective addition of silyl phosphites or phosphonites to cyclic 1-benzyloxycarbonyl enaminones. Interestingly, the hydride reduction of the resulting 2-phospho-4-oxopiperidine proceeds with high diastereofacial preference using NaBH₄. In the last step, the cleavage of N-Cbz group under hydrogenolysis followed by the hydrolysis of the phosphonate or phosphinate functionalities, led to the target cis-4-hydroxyphosphonic and cis-4-hydroxyphosphinic acids, respectively.

Synthesis of novel enantiopure 4-hydroxypipecolic acid derivatives with a bicyclic beta-lactam structure from a common 3-azido-4-oxoazetidine-2-carbaldehyde precursor

Two different stereocontrolled accesses to new 4-hydroxypipecolic acid analogues with a bicyclic beta-lactam structure have been developed by using intramolecular reductive amination or allenic hydroamination reactions in 2-azetidinone-tethered azides. The access to the cyclization precursors was achieved from 3-azido-4-oxoazetidine-2-carbaldehyde via metal-mediated carbonyl-allenylation in aqueous environment or by organocatalytic direct aldol reaction. The tin hydride-promoted cyclization of the 2-azetidinone-tethered azidoallene is totally regioselective for the central allenic carbon providing a fused piperidine.

Recent advances in asymmetric synthesis of pipecolic acid and derivatives

This review covers the literature relating to asymmetric syntheses of pipecolic acid derivatives from 1997 to present. This review is organized according to the position and the degree of substitution of the piperidinic cycle. In a first section, syntheses of pipecolic acid itself are described. Then, successively, syntheses of C-3, C-4, C-5, C-6 substituted pipecolic acid derivatives are reported. Finally, syntheses of unsaturated pipecolic acid derivatives are presented before the last part devoted to the polysubstituted pipecolic acid derivatives.

P4 cap modified tetrapeptidyl α-ketoamides as potent HCV NS3 protease inhibitors

We describe herein the design, syntheses, and biological evaluation of new series of P4 tetrazole and adipic acid, ester, amide capped tetrapeptidyl alpha-ketoamide based HCV protease inhibitors.

5-Substituted-1H-tetrazoles as carboxylic acid isosteres: medicinal chemistry and synthetic methods

5-Substituted-1H-tetrazoles (RCN4H) are often used as metabolism-resistant isosteric replacements for carboxylic acids (RCO2H) in SAR-driven medicinal chemistry analogue syntheses. This review provides a brief summary of the medicinal chemistry of tetrazolic acids and highlights some examples of tetrazole-containing drug substances in the current literature. A survey of representative literature procedures for the preparation of 5-substituted-1H-tetrazoles, focusing on preparations from aryl and alkyl nitriles, is presented in sections by generalized synthetic methods.