Highly efficient synthesis of (R)- and (S)-piperazic acids using proline-catalyzed asymmetric α-hydrazination

Enantioselective Synthesis of Chiral Cyclic Hydrazines by Ni-Catalyzed Asymmetric Hydrogenation

An efficient Ni-(S,S)-Ph-BPE complex that catalyzed asymmetric hydrogenation of cyclic N-acyl hydrazones has been developed to produce various chiral cyclic hydrazines in high yields with excellent enantioselectivities of up to >99% enantiomeric excess. Moreover, the hydrogenation can not only proceed smoothly on a gram scale under lower catalyst loading (S/C = 3000) without any decrease of enantioselectivity but can also be applied to the asymmetric synthesis of a RIP-1 kinase inhibitor.

Synthetic and biosynthetic routes to nitrogen-nitrogen bonds

The nitrogen-nitrogen bond is a core feature of diverse functional groups like hydrazines, nitrosamines, diazos, and pyrazoles. Such functional groups are found in >300 known natural products. Such N-N bond-containing functional groups are also found in significant percentage of clinical drugs. Therefore, there is wide interest in synthetic and enzymatic methods to form nitrogen-nitrogen bonds. In this review, we summarize synthetic and biosynthetic approaches to diverse nitrogen-nitrogen-bond-containing functional groups, with a focus on biosynthetic pathways and enzymes.

Organocatalysts based on natural and modified amino acids for asymmetric reactions

Small organic molecules predominantly containing C, H, O, N, S and P element are found promising molecule to accelerate chemical reactions and are named organocatalysis. In addition, these organocatalysts are easy availability, stable in water and air, inexpensive, and low toxicity, which confer a huge direct application in organic synthesis when compared to transition metal catalyzed reactions and becoming powerful tools in the construction of a selective chiral product. Interest on organocatalysis is spectacularly increased since last two decades, due to the novelty of the concept and selectivity. Based on the nature of the organocatalysts used, they are classified in to four major classes, among them one of the types is amino acids derived organocatalysts. Natural amino acids are playing important role in building blocks of protein construction, and also intermediate products of the metabolism. α-Amino acid is a molecule, that contains both amine and carboxyl functional group. Their particular structural characteristic determines their role in protein synthesis, and bifunctional asymmetric catalysts for stereoselective synthesis. Two functional groups present on a single carbon acting as an acid and base, which promote chemical transformations in concert similar to the enzymatic catalysis. The post translational derivatives of natural α-amino acids include 4-hydroxy-L-proline and 4-amino-L-proline scaffolds, and its synthetic variants based organocatalysts, whose catalytic activity is well documented. This chapter discussed past and present development of the organocatalysts derived from natural and modified amino acids for various important organic transformations reviewed.

A Reliable Enantioselective Route to Mono-Protected N1-Cbz Piperazic Acid Building Block

The chiral N1-Cbz, N2-H derivative of the piperazic acid monomer is a valuable building block in the total synthesis of natural products, comprising this nonproteinogenic amino acid. In that context, we wish to report an improved synthetic protocol for the synthesis of both (3R)- and (3S)-piperazic acids bearing the carboxybenzyl protecting group (Cbz) selectively at the N1 position. Our method builds on previously reported protocols, circumventing their potential shortcomings, and optimizing the ultimate selective deprotection at the N2 position, thus, offering an efficient and reproducible pathway to suitably modified piperazates in high optical purity.

Construction of enantioenriched polysubstituted hexahydropyridazines via a sequential multicatalytic process merging palladium catalysis and aminocatalysis

An efficient multicatalytic strategy for the construction of nitrogen-containing heterocycles has been reported. The powerful combination of organic and metal catalysis in a single vessel allowed the formation of enantioenriched polysubstituted cyclic 6-membered hydrazines bearing a quaternary stereocenter in good yields and selectivities.

Total synthesis of padanamides A and B

The first total syntheses of padanamides A and B have been achieved, unambiguously confirming their structures.

Towards the stereochemical assignment of natural lydiamycin A

A convergent approach leading to the stereoselective synthesis of four diastereomers of lydiamycin A has been established and verified.

An alternative convenient synthesis of piperidazine-3-carboxylic acid derivatives

The short-step synthesis of the unsubstituted, 5-hydroxy- and 5-chloropiperidazine-3-carboxylic acids using an aza Diels-Alder reaction between the 1,3-diene and azodicarboxylate was described. This synthetic methodology could be used for the preparation of the optically active piperazic acid in a 35% overall yield.

Organocatalytic Synthesis of (2S,3R)-3-Hydroxy-3-methyl-proline (OHMePro), a Component of Polyoxypeptins, and Relatives Using OHMePro Itself as a Catalyst

An efficient synthesis of (2S,3R)-3-hydroxy-3-methylproline (OHMePro), a component of polyoxypeptins, and relatives was achieved, in which an intramolecular asymmetric aldol reaction of the ketoaldehyde using OHMePro itself as an organocatalyst constitutes a key step.