Novel steroidal penta- and hexacyclic compounds derived from 12-oxospirostan sapogenins (original) (raw)
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Experimental section S2 2. Complete characterization of compounds 7-10 S3 3. Computational details S6 4. Details of X-ray collection, solution, and refinement of 10 S6 5. NMR spectra of compounds 7-10 S8 6. Cartesian coordinates of all the stationary points involved in the mechanism of transformation of 4 to 7 S28 7. References S41 S2 1. Experimental section General remarks Optical rotations were measured at 24 ºC in an Anton-Paar MCP500 polarimeter. 1 Hand 13 C-NMR spectra were recorded at 400 and 100 MHz, respectively, on a Varian Mercury NMR instrument and at 500 and 125 MHz on a Bruker Avance NMR instrument. The 1 H-NMR spectra were referenced to residual protonated solvent (δ 7.26 ppm) and the 13 C-NMR spectra to the middle signal of CDCl 3 (77 ppm). All assignments were confirmed with the aid of two-dimensional experiments (COSY, HSQC, and HMBC). Processing of the spectra was performed using MestReNova software. High-resolution mass spectra were obtained by the electrospray ionization (ESI) technique, using an Agilent 6230 TOF LC/MS mass spectrometer. IR spectra were recorded on an Agilent Cary 630 FTIR spectrometer (range: 4000-600 cm-1). Column chromatography was carried out using a Teledyne Isco Combiflash apparatus and analytical thin-layer chromatography (TLC) on aluminum plates precoated with Silica Gel 60F-254. General method for the synthesis of DHP derivatives The steroidal sapogenin (4, 5, or 6, 1 mmol) was dissolved in CH 2 Cl 2 (10 mL) and cooled down to 0 °C. A mixture of Ac 2 O (15 mmol) and BF 3. OEt 2 (15 mmol) was cooled (0 °C) and added dropwise to the steroidal sapogenin solution. The mixture was stirred for 5 min and poured into cold Et 3 N (-10 °C, 40 mmol). After 5 min a saturated solution of NH 4 OH (1 x 5 mL) was subsequently added. The organic phase was diluted with AcOEt, separated, filtered through silica gel, and evaporated under reduced pressure. The crude was purified by flash chromatography on a Combiflash apparatus using a gradient elution
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The title compound 2 was prepared from (20R)-pregn-5-ene-3β,20-diyl 3-acetate 20-benzoate (3) via (20R)-3β-acetoxy-20-benzoyloxy-5-oxo-5,6-secopregnan-6-oic acid (5) and (20R)-3β-acetoxy-20-benzoyloxy-7-nor-5β,6α-pregnane-6,5-carbolactone (6). An intermediate 7-norpregn-5-ene derivative – (20R)-7-norpregn-5-ene-3β,20-diyl 3-acetate 20-benzoate (7) –was hydrogenated using diimide in statu nascendi. The inversion of configuration at carbon C-3 was carried out via (20R)-7-nor-5α-pregnane-3β,20-diyl 3-tosylate 20-benzoate (12) and (20R)-7-nor-5α-pregnane-3α,20-diyl 20-benzoate 3-formate (13).