Glycal

About: Glycal is a research topic. Over the lifetime, 897 publications have been published within this topic receiving 17422 citations.

Convergent synthesis of polyether ionophore antibiotics: Synthesis of the spiroketal and tricyclic glycal segments of monensin

Abstract: The syntheses of the spiroketal II and tricyclic glycal III portions of the polyether antibiotic monensin (I) are described. The butyric acid side chain of spiroketal II is constructed through either Sharpless epoxidation of a cis-2-butenol residue or by Brown crotylation of an α-methylacetaldehyde unit. The spiroketal is then generated through a hetero-Diels-Alder addition between a tetrahydropyranoid methylene ketone and acrolein. Finally, [6.5] - spiroketal structure II is prepared by mild acid catalyzed rearrangement of [6.6]-spiroketal epoxide 23. Glycal III was made from the C/D subunit 44. This subunit was prepared by the ester enolate Claisen rearrangement that unites the tetrahydrofuranoid C and D rings 40 and 41 by Brown crotylation, Wittig condensation, and then cyclization to form the E ring. The synthesis of the two fragments set the stage for a final ester enolate Claisen rearrangement that will form the skeleton of the polyether monensin (I)

Anhydrodihydroartemisinin and Its 10-Trifluoromethyl Analogue: Access to Novel D-Ring-Contracted Artemisinin Trifluoromethyl Ketones

Abstract: The preparation of the 10-trifluoromethyl hydroartemisinin, followed by dehydration, afforded the trifluoromethyl analogue 2 of anhydrodihydroartemisinin 1. The reactivity of these two glycals of artemisinin were compared in epoxidation and halogenation reactions. Iodination of glycal 1 in water and the further rearrangement of the produced iodo hemiacetal provided the new D-ring-contracted aldehyde 8alpha, where the methyl at C-9 is beta. Epoxidation of 10-trifluoromethyl anhydrodihydroartemisinin 2 stereoselectively provided the beta-epoxy ether 11 in high yield. When treated with hexafluoro-2-propanol or trifluoroethanol, 11 readily underwent a rearrangement yielding to the D-ring-contracted trifluoromethyl ketone 9alpha with retention of configuration at C-9.