The Structure of a Degradation Product of 2-Mercaptopurine: 5-Amino-2-thiocytosine Dihydrochloride Dihydrate

Article abstract of DOI:10.1107/S0567740881007176

C4H8N4S²⁺*2Cl^-*2H2O (M_r=251.136) is orthorhombic, P2₁2₁2₁, with a=6.2236 (7), b=10.8285 (10), c=15.3729 (14) Angstroem (V=1036.0 Angstroem³), Z=4, d_c=1.610, d_o(flotation)=1.62 Mg m^-3.Full-matrix least-squares refinement using 2507 observed reflections 3?(I) with 2θ<90 deg converged at R=R_w=0.029 and S=1.4.Average e.s.d.'s in bonding are 0.0018 Angstroem and 0.12 deg (non-hydrogen atoms) except for values involving S, for which they are 0.0014 Angstroem and 0.11 deg.The molecular structure of the cytosine moiety is very similar to that of cytosine hydrochloride .The crystal structure consists of an extensive three-dimensional hydrogen-bonding network, with chains of 5-amino-2-thiocytosine molecules along the <010> direction linked through hydrogen bonds to the two Cl^- ions and one of the water molecules.Two of the H atoms of the -NH3⁺ group are involved in bifurcated hydrogen bonds.