Highly enantioselective synthesis of multifunctionalized allylic building blocks via oxazaborolidine-catalyzed borane reduction

Thiol-free multicomponent synthesis of non-racemic β-acyloxy thioethers from biocatalytically obtained chiral halohydrins

A novel multicomponent chemoenzymatic strategy for the preparation of enantioenriched β-acyloxy thioethers has been developed. This robust methodology employs mild bases, air atmosphere, room temperature and avoids the use of foul-smelling thiols. Instead, potassium thioacetate is employed as a universal sulfur source. This chemoselective strategy tolerates aromatic and aliphatic components and diverse functional groups. The chirality is enzymatically defined by ADH-catalyzed bioreduction of α-haloketones delivering an enantioenriched halohydrin which is one of the three components, and the optical purity remains untouched in the final product. Semipreparative scale multicomponent reaction affords high yield of the products (up to 96%).

β-Hydroxy sulfides and their syntheses

Sulfur-containing natural products are ubiquitous in nature, their most abundant source being marine organisms since sulfur, in the form of the sulfate ion, is the second most abundant anion in sea water after chloride. As part of natural products, sulfur can appear in a multitude of combinations and oxidation states: thiol, sulfide (acyclic or heterocyclic), disulfide, sulfoxide, sulfonate, thioaminal, hemithioacetal, various thioesters, thiocarbamate and isothiocyanate. This review article focuses on β-hydroxy sulfides and analogs; their presence in natural products, general protocols for their synthesis, and examples of their application in target oriented synthesis.

Regio- and enantio-selective oxidation of diols by Candida parapsilosis ATCC 7330

Optically pure (S)-diols and their corresponding hydroxy ketones were prepared via regio- and enantio-selective oxidation of the corresponding diols using whole cells of Candida parapsilosis ATCC 7330.

Spiroborate ester-mediated asymmetric synthesis of beta-hydroxy ethers and its conversion to highly enantiopure beta-amino ethers

Borane-mediated reduction of aryl and alkyl ketones with alpha-aryl- and alpha-pyridyloxy groups affords beta-hydroxy ethers in high enantiomeric purity (up to 99% ee) and in good yield, using as catalyst 10 mol % of spiroborate ester 1 derived from (S)-diphenylprolinol. Representative beta-hydroxy ethers are successfully converted to beta-amino ethers, with minor epimerization, by phthalimide substitution under Mitsunobu's conditions followed by hydrazinolysis to obtain primary amino ethers or by imide reduction with borane to afford beta-2,3-dihydro-1H-isoindol ethers. Nonracemic Mexiletine and nAChR analogues with potential biological activity are also synthesized in excellent yield by mesylation of key beta-hydroxy pyridylethers and substitution with five-, six-, and seven-membered ring heterocyclic amines.