Cholest-5-ene- and Stigmasta-5,22-diene-Based 1,3-Oxathiolan-5-one Lactones and an Aminothiazole–Diosgenin Hybrid: Synthesis and Preliminary Antimicrobial Activity

Novel steroidal heterocyclic derivatives were prepared from cholesterol, stigmasterol, and diosgenin scaffolds via concise, reagent-efficient synthetic routes. Two 1,3-oxathiolan-5-one derivatives bearing cholest-5-ene (7) and stigmasta-5,22-diene (8) cores were obtained from the corresponding steroidal ketones through hydrazone formation, phenyl isothiocyanate addition, and S-selective cyclization with chloroacetic acid in refluxing toluene. An aminothiazole–diosgenin hybrid (12) was independently prepared via regioselective α-bromination of an oxidized diosgenin intermediate followed by condensation with thiourea in ethanolic sodium ethoxide. The newly synthesized target compounds were characterized by FT-IR, 1H- and 13C-NMR spectroscopy, ESI mass spectrometry, and elemental (CHNS) analysis. The disc-diffusion assay against S. aureus and E. coli was retained only as a preliminary qualitative screen because no positive antibiotic control or MIC determination was included. Within this limited screen, compound 12 produced measurable 8.5–9.0 mm inhibition zones against both strains, supporting their prioritization for future standardized antimicrobial testing rather than establishing comparative potency.