Molecular rearrangements of poststerone derivative steroid core with formation of unique D-homostructures of pregnane and androstane series

In vitro adjuvant antitumor activity of various classes of semi-synthetic poststerone derivatives

“…The hydride reduction of poststerone 2 with an equimolar amount of L-Selectride resulted in the regio-and stereospecific formation of 20Ralcohol 5. A similar reduction of the 20-oxo moiety of pregnane ecdysteroids on treatment with a 1.5-molar amount of organohydride reagent was carried out previously for compound 6 [18], whereas the reduction with a two molar amount of L-Selectride led to the transformation of 6,20-diketo groups accompanied by epimerization at 5-H and gave 6α,20R alcohol 7 of 5α-pregnane series [18].…”

“…In the case of ecdysteroids, fluorination of 2,3;20,22-diacetonide of 20E increased the inhibitory activity of derivatives against overexpression of ABCB1, but in most cases, it affected the chemosensitizing activity of compounds [27]. Fluorination of pregnane 20R-alcohols with the DAST reagent yielded products with a transformed carbon skeleton, instead of the expected fluoro derivatives [18]. The 13(14 → 17a)-abeo-rearrangement of 20Ralcohol 6 resulted in a skeletal transformation and gave 13,14-secoandrostane structure 8.…”

“…Previously, we demonstrated that poststerone derivatives undergo skeletal transformations on treatment with the organohydride reagent L-Selectride [18] or via ultrasonically assisted 2,3-dideoxygenation reaction (NaI-Zn-DMF) to give 13(14 → 8)-abeo-ecdysteroids resulting from intramolecular rearrangement [19]. This type of transformations accompanied by migration of the C13-C14 bond with simultaneous contraction/expansion of the steroid C/D-rings are driven by the presence of the reactive allylic 14-OH group and could be classified as semipinacol rearrangement of allylic tertiary alcohols initiated by Lewis or Brønsted acids [20].…”

“…This type of transformations accompanied by migration of the C13-C14 bond with simultaneous contraction/expansion of the steroid C/D-rings are driven by the presence of the reactive allylic 14-OH group and could be classified as semipinacol rearrangement of allylic tertiary alcohols initiated by Lewis or Brønsted acids [20]. Another skeletal modification of pregnane 20Rhydroxyecdysteroids is induced by DAST (diethylaminosulfur trifluoride) resulted in the diastereoselective formation of (20R)-13(17 → 20)-D-homo-or 13,14-seco-androstane structures [18].…”

Diethylaminosulfur Trifluoride (DAST) Mediated Transformations Leading to Valuable Building Blocks and Bioactive Compounds

“…This transformation has been observed in steroids. [74] Unexpected results were observed by Savchenko and coworkers during the fluorination attempt of alcohols 234 and 239 using DAST (Scheme 51, Scheme 52). [74a] The ecdysteroid 239 was transformed into compound 243 instead of the 20fluoro derivatives.…”