BF₃·Et₂O-induced stereoselective aldol reaction with benzaldehyde, and steroid sapogenins and its application to a convenient synthesis of dinorcholanic lactones

An unexpected acid-catalyzed rearrangement of diacetoxy benzylidenespirostanes to spirochromene acetals and spiroindenes with radical scavenger activity

23E-diacetoxybenzylidenespirostanes underwent rearrangement when treated with HCl in CH₂Cl₂/CH₃OH. The course of the rearrangement depends on the substitution pattern in the phenyl ring. While compounds bearing an acetoxy group at the ortho position produced spirochromenes, the partners with no substituent at the ortho position led to spiroindenes. All the rearranged compounds exhibited moderate antioxidant activity.

Reductive desymmetrization of steroid dimers

NaBH₃CN reduction of symmetric dimers in which two steroid units are linked by a 1,4-dimethylidenebenzene moiety followed two different courses: (a) hydrogenation of the benzylic double bond and (b) reductive F ring opening of the side chain. While courses a and b led to symmetrical dimers, the combination of both pathways produced an unsymmetrical dimer that bears different side chains in each half. The exhaustive NMR characterization of all obtained compounds is presented.

Studies on the reactivity of 23E-benzylidene spirostanes

A study of the reactivity of 25R and 25S 23E-benzylidene spirostanes that includes epoxidation, catalytic hydrogenation as well as Lewis or Brønsted acid-catalyzed rearrangements is described. Exhaustive NMR characterization of the obtained compounds is presented. Additionally the structures of some of the obtained compounds were confirmed by single crystal X-Ray Diffraction studies.

Synthesis of dimeric spirostanols linked through a 1,4-dimethylidenebenzene moiety by double BF3·Et2O-catalyzed aldol condensation of steroid sapogenins and terephtalaldehyde

BF₃·Et₂O-catalyzed double aldol condensation between acetylated steroid sapogenins and terephtalaldehyde led to acetylated dimeric spirostanols linked through a 1,4-dimethylidenebenzene moiety in moderate to good yields. The E configurations of the introduced double bonds were corroborated by NOE experiments. Saponification of the dimeric steroids led to the corresponding dimeric spirostanols.

Baeyer-Villiger reaction of steroid sapogenins by CF3COOH-H2O2. A short cut to pregnan-3β,16β,20-triol 3-monoacetates

Treatment of steroid sapogenins with H₂O₂ in CF₃COOH for 15min followed by reflux in CH₃OH/H₂O afforded good yields of pregnan-3β,16β,20-triol 3-monoacetates. When the hydrolysis step was carried out with KOH in refluxing methanol excellent yields pregnantriols were obtained. The resulting compounds were characterized by their melting points and NMR spectral data. An X-ray diffraction analysis of compound 3a confirmed the proposed structure and provided detailed information about the bond lengths, bond angles and conformation.

Synthesis of novel hybrid steroid dimers by BF3·Et2O-catalyzed aldol condensation of 2-formyl-estradiol diacetate and steroid sapogenins

BF₃·Et₂O-catalyzed aldol condensation of steroid sapogenins with 2-formyl-estradiol diacetate afforded two novel classes of steroid dimers in which an estrogenic core is attached to the spirostanic side chain of an steroid sapogenin through an exocyclic double bond in position C-23, or through a spiro centre in C-22.

Synthesis and in vitro anticancer activity of 23(23')E-benzylidenespirostanols derived from steroid sapogenins

Benzylidenespirostanols were prepared by two-step synthesis including BF₃·Et₂O-catalyzed aldol condensation of several acetylated steroid sapogenins with benzaldehyde followed by saponification. The obtained compounds showed moderate cytotoxicity against three cancer cell lines (T-lymphoblastic leukemia cell line CEM, breast carcinoma cell line MCF7 and cervical carcinoma cell line HeLa) and normal human fibroblasts (BJ). The most active of the five tested substances was 3c (lowest IC₅₀ for MCF7 cells 19.9±0.1µM) without any selectivity towards human cancer and normal cells, respectively.

Total Synthesis of Linckosides A and B, the Representative Starfish Polyhydroxysteroid Glycosides with Neuritogenic Activities

Linckosides A and B, two starfish metabolites with promising neuritogenic activities, are synthesized in a longest linear sequence of 32 steps and 0.5% overall yield; this represents the first synthesis of members of the polyhydroxysteroid glycoside family, which occur widely in starfishes.

Synthesis and radical scavenger properties of novel spirochromenes derived from steroid sapogenins

Tandem aldol condensation between steroid sapogenins and hydroxylated benzaldehydes afforded steroidal spirochromenes. Compounds that bear a phenolic hydroxyl group at position C-6', obtained by a reaction with 2,5-dihydroxybenzaldehyde, showed approximately 80% of maximal radical scavenging activity in the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) assay at 288 nM. In contrast, the starting steroid sapogenins and the spirochromenes without a phenolic group in the side chain proved to be inactive.

Heterocyclizations of pregnenolone: novel synthesis of thiosemicarbazone, thiophene, thiazole, thieno[2,3-b]pyridine derivatives and their cytotoxicity evaluations

Pregnenolone (1) was used as a template to develop new anticancer compounds. Ring D modification of 1 through its reaction with 4-phenyl-3-thiosemicarbazide gave the thiosemicarbazone derivative 3. The latter compound underwent heterocyclization reactions to give the thiazolyl hydrazonoandrostane and pyrazolyl semicarbazidoandrostane derivatives 5a-d, and 9a-d, respectively. On the other hand compound 1 reacted with either malononitrile or ethyl cyanoacetate to give the Knoevenagel condensated products 11a and 11b, respectively. Compounds 11a,b afforded the thiophenyl pregnane derivatives 12a and 12b, respectively, their reactivity toward some chemical reagents was studied. The cytotoxicity of the newly synthesized heterocyclic steroids against three human tumor cell lines namely breast adenocarcinoma (MCF-7), non-small cell lung cancer (NCI-H460) and CNS cancer (SF-268) were studied. Some of tested compounds were found to exhibit much higher inhibitory effects toward the three tumor cell lines than the reference drug, doxorubicin.