THE CRYSTAL-STRUCTURE AND MOLECULAR-STRUCTURE OF 2'-DEOXYCYTIDINE - POLYMORPH-BETA

The structure of a polymorphic form of 2'-debxycytidine, unknown till now, is presented. There are three different molecules of 2'-dcoxycyti dine (named A, B and C) in an independent crystallographic unit. The p reviously described structure of 2'-deoxycytidine (1) consists of two molecules in an asymmetric unit. (C(9)H(13)N(3)O4)dr Mr=681.72, monocl inic, P2(1), a=13.9539(7), b=7.1007(3), c=15.8285(7) Angstrom, beta=10 4.163(4), V=1520.7(1) Angstrom(3), Z=6, Dx=1.49 g cm(-3), lambda(CuK a lpha)=1.54178 Angstrom, mu=1.007 cm(-1), F(000)=720, T=291K, R=0.0378 for 1993 observed reflections, There is a very interesting system of h ydrogen bonding among the molecules of 2'-deoxycytidine. The ribose pu ckering For molecules A and B of 2'-deoxycytidine are C(2')-endo-C(3') exo [P= 171.8(5), tau(m)=33.8(3) and P= 182.7(3), tau(m)=36.9(3) for A and B respectively], and C(2')-endo [P= 160.7(6), tau(m)=40.0(4)] for molecule C. The glycosyl torsion angles chi [C(2)-N(1)-C(1')-O(4)] ar e anti in all molecules [-153.6(3), -170.3(3) and -143.1(4) for A, B a nd C respectively]. There is a disorder of C5' and O(5') atoms in mole cule A, therefore the side chain in A exists in two conformations: -sc ; gamma[O(5')-C(5')-C(4')-C(3')]=-74.4(9) and -ac; gamma=-125(1). Mole cules B and C have -sc conformations with gamma=-75.7(5) and gamma=-72 .3(5) for molecules B and C, respectively.