Efficient synthesis of 2′-deoxyzebularine and its α-anomer by the silyl method of N-glycosylation. Crystal structures and conformational study in solution
摘要:
2'-Deoxyzebularine and its alpha-anomer have been efficiently synthesized with relatively high stereoselectivity by a modified procedure of the silyl method of the N-glycosidic bond formation. An SnCl4-catalyzed condensation of silylated pyrimidin-2-one with 1-alpha-chloro-3,5-di-O-p-toluoy1-2-deoxy-D-ribofuranose under kinetic control condition (-33 degrees C, 1,2-dichloroethane) led to the mixture of beta- and alpha-anomeric nucleosides in 3:1 ratio. Analogous condensation at +35 degrees C (thermodynamic control conditions) provided mainly p-toluoyl protected alpha-2'-deoxyzebularine (alpha:beta= 4:1), easily separated by crystallization from the anomeric mixture. The structures of both 2'-deoxyzebularine anomers were confirmed by X-ray analysis of the crystals and conformational studies in solution performed using an NMR method. (C) 2014 Elsevier Ltd. All rights reserved.