1-(beta-D-Erythrofuranosyl)adenosine

The title compound, also known as beta-erythroadenosine, C(9)H(11)N(5)O(3), (I), a derivative of beta-adenosine, (II), that lacks the C5' exocyclic hydroxymethyl (-CH(2)OH) substituent, crystallizes from hot ethanol with two independent molecules having different conformations, denoted (IA) and (IB). In (IA), the furanose conformation is (O)T(1)-E(1) (C1'-exo, east), with pseudorotational parameters P and tau(m) of 114.4 and 42 degrees, respectively. In contrast, the P and tau(m) values are 170.1 and 46 degrees, respectively, in (IB), consistent with a (2)E-(2)T(3) (C2'-endo, south) conformation. The N-glycoside conformation is syn (+sc) in (IA) and anti (-ac) in (IB). The crystal structure, determined to a resolution of 2.0 A, of a cocrystal of (I) bound to the enzyme 5'-fluorodeoxyadenosine synthase from Streptomyces cattleya shows the furanose ring in a near-ideal (O)E (east) conformation (P = 90 degrees and tau(m) = 42 degrees) and the base in an anti (-ac) conformation.