Novel structural aspects of oxythiamine, an antagonist of thiamine. Crystal structures of three salts, (oxythiamineH)(picrolonate)(2)center dot 2H(2)O, (oxythiamineH)(PtCl6), (oxythiamineH)(2)(V10O28H2) center dot 8H(2)O, and a metal complex Pt(oxythiamine)Cl-3 center dot H2O

Three salts of oxythiamine, (oxythiamineH)(picrolonate)(2). 2H(2)O (1), (ox ythiamineH)(PtCl6) (2) and (oxythiamineH)(2)(V10O28H2). 8H(2)O (3), and a m etal complex Pt(oxythiamine)Cl-3. H2O (4) have been prepared and characteri zed by X-ray diffraction. In the salts 1, 2 and 3, the oxythiamine molecule exists as a divalent cation with both the N(1') and the N(3') sites proton ated. In 1, oxythiamine adopts a novel conformation termed as the V'-form: with phi(T) = - 63.1(6) and phi(P) = - 54.7(6)degrees, where the oxo O(4'al pha) makes an electrostatic interaction with the thiazolium ring to stabili ze the V'-form. 2 and 3 are the first crystal structures in which oxythiami ne assumes the F-conformation, with phi(T) and phi(P) being - 5.3(9) and - 84.8(7)degrees, respectively, for 2, and 3.9(4) and 76.6(3)degrees for 3. I n 2 and 3 the anion-bridge of the type C(2)-H...anion...pyrimidine ring sta bilizes the F-form, where the anion is a PtCl62- ion in 2 and a decavanadat e ion in 3. The water-bridge of the type O(4'alpha)...water...thiazolium ri ng and the anion-bridge of the C(6')-H...anion...thiazolium ring type are a dditional structural features which stabilize the F-form in 3. The metal co mplex 4 provides the first X-ray example showing the direct metal bonding t o oxythiamine. The N(1')-metallated oxythiamine is in the usual V-conformat ion with phi(T) = 104.0(9) and phi(P) = - 72.6(8)degrees, which is stabiliz ed by a close contact between O(4'alpha) and the thiazolium moiety. (C) 199 9 Elsevier Science S.A. All rights reserved.