Robust and Efficient, Yet Uncatalyzed, Synthesis of Trialkylsilyl-Protected Cyanohydrins from Ketones

The synthesis of 4-chloro-17β-hydroxymethyl-17α-methyl-18-norandrosta-4,13-diene-3α-ol - Proposed long term metabolite (M4) of oralturinabol

4-Chloro-17β-hydroxymethyl-17α-methyl-18-norandrosta-4,13-diene-3α-ol is one of proposed long term metabolites of oralturinabol (anabolic androgenic steroid restricted in sport). The synthesis of 4-chloro-17β-hydroxymethyl-17α-methyl-18-norandrosta-4,13-diene-3α-ol was achieved. Isomerisation of configuration of 13-carbon was used for construction of 17β-hydroxymethyl-17α-methyl fragment. The proposed route of synthesis allows to obtain 3β-hydroxy isomer as well.

Synthesis of robalzotan, ebalzotan, and rotigotine precursors via the stereoselective multienzymatic cascade reduction of α,β-unsaturated aldehydes

A stereoselective synthesis of bicyclic primary or secondary amines, based on tetralin or chroman structural moieties, is reported. These amines are precursors of important active pharmaceutical ingredients such as rotigotine (Neupro), robalzotan, and ebalzotan. The key step is based on a multienzymatic reduction of an α,β-unsaturated aldehyde or ketone to give the saturated primary or secondary alcohol, in a high yield and with a high ee. The catalytic system consists of the combination of an ene-reductase (ER; i.e., OYE2 or OYE3 belonging to the Old Yellow Enzyme family) with an alcohol dehydrogenase (ADH), applying the in situ substrate feeding product removal technology. By this system the formation of the allylic alcohol side product and the racemization of the chirally unstable α-substituted aldehyde intermediate are minimized. The primary alcohols were elaborated via a Curtius rearrangement. The combination of OYE2 with a Prelog or an anti-Prelog ADH allowed the preparation of the secondary alcohols with ee > 99% and de > 87%. The absolute configuration of the primary amines was unambiguously assigned by comparison with authentic samples. The stereochemistry of secondary alcohols was assigned by X-ray crystal structure and NMR analysis of Mosher esters.

Kinetics and mechanism of the racemic addition of trimethylsilyl cyanide to aldehydes catalysed by Lewis bases

The mechanism by which four Lewis bases, triethylamine, tetrabutylammonium thiocyanate, tetrabutylammonium azide and tetrabutylammonium cyanide, catalyse the addition of trimethylsilyl cyanide to aldehydes is studied by a combination of kinetic and spectroscopic methods. The reactions can exhibit first or second order kinetics corresponding to three different reaction mechanisms. Spectroscopic evidence for the formation of hypervalent silicon species is obtained for reaction between all of the tetrabutylammonium salts and trimethylsilyl cyanide. The reactions are accelerated by the presence of water in the reaction mixture, an effect which is due to a change in the reaction mechanism from Lewis to Brønsted base catalysis. Tetrabutylammonium thiocyanate is shown to be an excellent catalyst for the synthesis of cyanohydrin trimethylsilyl ethers on a preparative scale.