Different conformations of 1-deazaadenosine and its 2 `-deoxyribonucleoside in the solid state and in solution

Abstract

Crystallization of 1-deaza-2'-deoxyadenosine (c(1)A(d), 1) from propanol-2 gives two forms of crystals: type A formed firstly as plates, then, on the surface of the plates, type B appeared as needles. Single crystal X-ray analyses shows that the crystals A and B differ mainly in the sugar ring conformation: A adopts the S-type (P = 179.8 degrees; C-2'-endo-C-3'-exo; T-2(3)) conformation associated with an high-anti base orientation (chi = -90.7 degrees) and the gamma = 152.3 degrees across the exocyclic C(4')-C(5') bond; B shows N-type (P = 21.2; C-3'-endo; E-3) conformation accompanied by a somewhat different anti base orientation (chi = -116.5 degrees) an eclipsed orientation of the exocyclic C(4')-C(5') bond (gamma = 84.5 degrees). No intramolecular hydrogen bonds in both types of crystals can be detected. Unlike c(1)A(d), the ribonucleoside (c(1)A, 2) is in the syn conformation (chi = 56.1 degrees) in the solid state which is caused by an intramolecular (5')CH2OH ... N(3) hydrogen bond. The compounds 1 and 2 display very similar conformation in D2O solution with a strong preference for the S-type conformation of the furanose ring accompanied by the intramolecular (5')CH2OH ... N(3) hydrogen bond. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.