Photoinduced Isomerization of 23-Oxosapogenins: Conformational Analysis and Spectroscopic Characterization of 22-Isosapogenins

Steroidal Molecular Rotors with 1,4-Diethynylphenylene Rotators: Experimental and Theoretical Investigations Toward Seeking Efficient Properties

Properly designed molecular rotors with sizable stators and a fast-moving rotator could provide efficient building blocks for amphidynamic crystals. Herein, we report the synthesis of steroidal compounds 1, 2, and 3 and their deuterated analogues 1D, 2D, and 3D envisioned to work as molecular rotors. The obtained compounds were characterized by attenuated total reflection-infrared, Raman, and circular dichroism (CD) spectroscopy measurements. The interpretation of spectra was supported by theoretical calculations using density functional theory methods. The analysis of the most characteristic bands confirmed different molecular dynamics of the rotors investigated. Angle-dependent polarized Raman spectra showed the crystallinity of some samples. Electronic CD (ECD) spectra of compounds 1–3 and their relevant deuterated analogues 1D–3D are identical. The increase of the band intensity with lowering the temperature shows that the equilibrium is shifted to the thermodynamically most stable conformer. ECD spectra simulated at the TDFFT level of theory for compound 3 were compared with experimental results. It was proved that conformer 3a, with a torsion angle of +50°, exhibits the best agreement with the experimental results. Simulated vibrational CD and IR spectra for conformer 3a and its deuterated analogue 3Da also display good agreement with experimental results. In light of our comprehensive investigations, we evidenced that steroidal compounds 1, 2, and 3 can work as molecular rotors.

Stereospecific synthesis and rearrangement of 22S-23-acetylsapogenins

The BF₃·Et₂O-catalysed acetolysis of steroid sapogenins diosgenin, sarsasapogenin and tigogenin in dichloromethane as the solvent instead of acetic anhydride afforded (20S)- and (20R)-22,26-epoxycholestanes (compounds 1 and 2). 22S-23-Acetylsapogenins (compounds 4) were synthesized stereospecifically from 20R-22,26-epoxycholestanes (compounds 2) in good yield. The rearrangement of 22S-23-acetylsapogenins (compounds 4) afforded novel disubstituted dihydropyran furostanol frameworks. Exhaustive NMR characterization of the obtained compounds is provided. Additionally, the structures of the critical compounds (6a and 7a) were unequivocallyconfirmed by single crystal X-ray diffraction studies.

Revision of the Structure of N, O-Diacetylsolasodine. Unusual Epimerization at the Spiro Carbon Atom during Acetylation of Solasodine

The steroidal alkaloid solasodine (1) undergoes inversion of configuration at the C-22 spiro atom when treated with acetic anhydride-pyridine at ambient temperature. The basic solvolysis of the N, O-diacetyl derivative (2) reverses the reaction, yielding the starting solasodine (1). The mechanisms of both processes (acetylation and deacetylation) were studied in terms of possible reaction pathways.

Erroneous epimerization at C-22 in sapogenins

A recent report [1] about the epimerization of steroidal sapogenins at C-22 by treatment with BF3 · OEt2 is incorrect. We proved that the epimerization of sapogenins with BF3 · OEt2 occurs at C-25 as in the case of other acid-catalyzed reactions previously studied.

Chromane helicity rule – scope and challenges based on an ECD study of various trolox derivatives

The validity of the chromane helicity rule is examined using a set of natural (S)-trolox derivatives.