PTERIDINE STUDIES .38. CRYSTAL AND MOLECULAR STRUCTURE OF COVALENT ADDITION PRODUCT OF 2-AMINOPTERIDINE HYDROBROMIDE AND ETHANOL

2-Amino-4-ethoxy-3,4-dihydropteridin-1-ium bromide is confirmed by X-ray analysis to be the nucleophilic addition product of 2-aminopteridine hydrobromide and ethanol. The crystals are triclinic with a 12.63, b 6.540, and c 7.074 Å and α 96.67°, β 98.33°, and γ 90.59°. and the space group is P1. The bromide ion, the carbon, nitrogen, and oxygen atoms and four of the twelve hydrogen atoms were located from Patterson, electron density, and difference maps respectively. Full-matrix least-squares refinement reduced R to 0.144 for 1968 reflexions. C(2) and the three nitrogen atoms bonded to it form a planar guanidinium system, all four hydrogen atoms being used up in the hydrogen-bonding network to the bromide ions. The pyrazine ring is also planar as is roughly the C(4)ethoxy-unit which makes an angle of about 84° with the mean plane through all the ring atoms.