Vitamin D: Enantioselective Synthesis of (3aR,4R,7aS)-4-Hydroxy-7a-methylperhydro-1-indenone, a Suitable CD-Ring Fragment

Synthesis and vitamin D receptor affinity of 16-oxa vitamin D3 analogues

Two novel 16-oxa-vitamin D₃ analogues were synthesized using a tandem Ti(ii)-mediated enyne cyclization/Cu-catalyzed allylation, Ru-catalyzed ring-closing metathesis reaction, and a low-valent titanium (LVT)-mediated stereoselective radical reduction of 8α,14α-epoxide as the key steps for the synthesis of the 16-oxa-C,D ring unit. The vitamin D receptor-binding affinity of the synthesized analogues, 16-oxa-1α,25-(OH)₂VD₃ and 16-oxa-19-nor-1α,25-(OH)₂VD₃, was evaluated by fluorescence polarization vitamin D receptor competitor assay and time-resolved fluorescence energy transfer vitamin D receptor co-activator assay.

Unexpected Racemization in the Course of the Acetalization of (+)-(S)-5-Methyl-Wieland–Miescher Ketone with 1,2-Ethanediol and TsOH under Classical Experimental Conditions

(+)-(S) and (−)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (−)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (−)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean–Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected racemization are provided.

Total Synthesis of (±)-Pallavicinin and (±)-Neopallavicinin

Through a biomimetic pathway, (+/-)-pallavicinin and (+/-)-neopallavicinin were synthesized from (+/-)-Wieland-Miescher ketone via Grob fragmentation, intramolecular aldol cyclization, and intramolecular Michael reaction. The synthesis was stereocontrolled efficiently and followed the stereochemistry of the Wieland-Miescher ketone, and could provide opportunities for access to analogues of pallavicinin, neopallavicinin, and other related bioactive diterpenoids.