The biosynthesis of spermidine. Part 2: preparation and study by 1H n.m.r. spectroscopy of hexahydropyrimidines from spermidine and propane-1,3-diamines

The reaction of spermidine with 1 mol equiv. of ethanal yields 1-(4′-aminobutyl)-2-methylhexahydropyrimidine, whilst spermidine and 2 mol equiv. of ethanal afford 1-[4′-(N-ethylidene)aminobutyl]-2-methylhexahydropyrimidine. These assignments are based on the results of 1H n.m.r. spectroscopic experiments and mass spectral analyses, supported by data for a series of model compounds. The 400 MHz 1H n.m.r. spectra of the hexahydropyrimidines from spermidine and of other hexahydropyrimidines (2-methyl-, 2-benzyl- and 1,2-dimethyl-) were analysed with the aid of computer-assisted spectral simulations. The model substances 2-methyl- and 2-benzyl-hexahydropyrimidine were converted into N,N-diacetyl derivatives. The 1H n.m.r. spectra of these derivatives show that they possess one acetyl group with its oxygen syn to C-2 and the other acetyl with its oxygen anti to C-2.