SYNTHESIS OF SPINACINE AND SPINACINE DERIVATIVES - CRYSTAL AND MOLECULAR-STRUCTURES OF N-PI-HYDROXYMETHYL SPINACINE AND N-ALPHA-METHYL SPINACEAMINE

The natural amino acid L-Spinacine -tetrahydro-1H-imidazo[4,5-c]pyridi ne-6-carboxylic acid) has been synthesized following a new pathway whi ch gives a chemically and optically pure product with an excellent yie ld. The crystal structures of a synthetic intermediate, N-pi-hydroxyme thyl-spinacine, and a spinacine derivative, N-alpha-methyl-spinaceamin e, have been investigated through X-ray diffraction: Spi(pi MeOH) . H2 O, monoclinic P2(1), a = 8.571(1), b = 6.682(1), c = 8.588(1)Angstrom, and beta = 94.67(1)degrees. Spm(alpha Me) . 2HCl . H2O, triclinic P ( 1) over bar, a = 7.492(4), b = 10.799(3), c = 7.040(2) Angstrom, alpha = 91.88(2), beta = 98.36(3) and gamma = 73.34(3)degrees. Spi(pi MeOH) crystallizes with a water molecule and displays a zwitterionic charac ter. The carboxylate group is in equatorial position and forms a short electrostatic interaction of 2.618(2) Angstrom between one of its oxy gens and the protonated nitrogen of the tetrahydropyridine ring. The c rystal packing is assured by strong O-H---O, O-H---N, N-H---N intermol ecular hydrogen bonds and C--H---O close contacts. The biprotonated co mpounds Spm(alpha Me) crystallizes with two Cl- anions and a water mol ecule. The positive charge on the imidazole ring is delocalized on the conjugated moiety N=C-N. The crystal is built up by clusters formed b y two biprotonated Spm(alpha Me) molecules, four Cl- anions and two wa ter molecules linked together by hydrogen bonds.