A new approach to the side chain formation of 24-alkyl-22-hydroxy steroids: application to the preparation of early brassinolide biosynthetic precursors

Enantioselective catalytic approach to the C23-C28 subunit of 24α-methyl steroids

Enantioselective synthesis of C23-C28 subunit of campestane steroids based on catalytic methods is reported. The synthesis was started from (S)-2-isopropyl-4-nitrobutan-1-ol, which is easily accessible by the reaction between isovaleraldehyde and nitroethylene catalyzed by only 2% of (S)-trimethylsilyldiphenylprolinol. Removal of one "extra" carbon from the nitroalcohol was achieved by Ni-catalyzed hydrodecarboxylation of the redox-active ester intermediate. The synthesized C23-C28 fragment was attached to a steroidal core by Julia-Kocienski reaction of a steroidal aldehyde with metallated C23-C28 sulfone. The obtained product of olefination was easily transformed to a precursor of campesterol and (Z)-22-dehydrocampesterol.

Stereoselective synthesis of α-methyl and α-alkyl ketones from esters and alkenes via cyclopropanol intermediates

Alkenes bearing a stereocenter in the allylic position were found to undergo Kulinkovich hydroxycyclopropanation with good diastereoselectivity. For the isomerization of the resulting cyclopropanols to diastereomerically enriched α-methyl ketones, a new mild regioselective method has been developed. A sequence of stereoselective cyclopropanation and cyclopropanol ring opening was successfully employed for the construction of the C20 stereocenter in steroids.

Brassinosteroid-BODIPY conjugates: Design, synthesis, and properties

Three BS-BODIPY (brassinosteroids-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) conjugates were synthesized and their fluorescent and immunological properties were investigated. Two of the conjugates, having present all the functional groups characteristic of BS, were shown to be potentially useful as biological probes to study involvement of BS into physiological processes in living cells.