The Crystal Structure of Anhydrous Xanthosine Displays Intramolecular 0(2')H ... 0(3') Hydrogen Bond
نویسندگان
چکیده
From an equimolar dipeptide/xanthosine mixture in water/methanol, only the nucleoside crystallized in anhydrous form, space group P2,2,2, with a = 17.406 (5) A, 6 = 12.378 (4), c= 5.350 (2) A, Z = 4, C|0H 12O6N4, FW = 284.26, D x = 1.639 g • cm-3. The structure was deter mined by direct methods on the basis of 984 X-ray data and refined to an agreement index of R = 3.9%. Xanthosine occurs in the syn conformation with / = 132.7° which is stabilized by an intramolecular hydrogen bond N(3)-H ... 0(5')The pseudorotation parameters for sugar puckering are P = 156° and tm = 38.7° corresponding to C(2')-endo form. The crystal packing of xanthosine in anhydrous and dihydrate modifications are very different, yet the molecular conformations are similar. In the anhydrous form, an unusual intramolecular hydrogen bond 0(2 ')-H ... 0(3') is observed.
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