Mass spectra of 1,19-epoxycardenolides
The mass spectra of six 18,19-epoxycardenolides (ECs) with various substituents in the 3β position — OH, OAc, rhamnosyloxy have been studied. In all the spectra the contribution of the fragments characteristic for cardenolides formed by the cleavage of the bonds of rings C and D were lowered. The strongest peaks were those of ions with m/z 259, 272, and 285 arising on the splitting out of the elements of rings A and B. It was established by the metastable defocusing (MD) method that in the case of the 3β-ols these fragments are formed from M+ and in the case of acetyl derivatives, in addition, they may arise from the (M — AcOH)+ ions. The spectra of the epoxycardenolides were compared with the structure of 3β,5β,14β,19-tetrahydroxycardenolide (strophanthidol) and its 3β-monoacetate and 3β,19-diacetate. The MD spectra and elementary compositions of the ions showed that other mass-spectrometric conditions strophanthidol monoacetate decomposes partially in the form of the 8,19-epoxycardenolide.
Mass spectrometry in cardenolide chemistry—II
Six partial acetates of gitoxin have been used to establish the value of mass spectrometry, when used in conjunction with deuteroacetylation, in cardenolide structural studies. This technique permits the unambiguous location of acetyl groups upon any of the digitoxose residues, and in some cases confirms acetylation of C16 of the steroid ring. The method is suitable for metabolic studies. The spectra discussed show that neither acetyl exchange nor acetyl migration reactions had taken place during the deuteroacetylation step.
Catalytic removal of tert-butyldimethylsilyl (TBS) ether by PVP-I
Abstract A mild, efficient and rapid protocol the deprotection of alcoholic TBDMS ethers using PVP-1 as catalyst in methanol, the procedure of deprotection of various TBDMS ethers were found to be very convenient, easy work-up, high yielding.