Degradation chemistry of a Vitamin D analogue (ecalcidene) investigated by HPLC–MS, HPLC–NMR and chemical derivatization

Ecalcidene (1-[(1α,3β,5Z,7E,20S)-1,3-dihydroxy-24-oxo-9,10-secochola-5,7,10(19)-trien-24-yl]-piperidine) is a new 1-hydroxyvitamin D analogue. In this report, the thermal degradation, acid induced degradation and iodine induced degradation of ecalcidene were investigated using HPLC–MS, HPLC–NMR and chemical derivatization. In solution ecalcidene was thermally and reversibly transformed to a pre-Vitamin D type isomer 1 which subsequently produced the dehydrated pyrocalciferol and isopyrocalciferol type isomers 2 and 3 by cyclization and dehydration at elevated temperatures. Acidic conditions resulted in the formation of a novel C9-hydroxylated isomer 4 of ecalcidene, possibly via a tachysterol type intermediate, followed by the acid facilitated nucleophilic addition of water. In the presence of iodine, cis/trans isomerization of both ecalcidene and its pre-Vitamin D type isomer 1 occurred. The results may shed light on the stability and metabolism of ecalcidene, provide useful information for its potential pharmaceutical development, and enrich the knowledge of Vitamin D chemistry.