STRUCTURE OF A PYRIMIDINE AMINO ACID FROM PEA SEEDLINGS

1. 1. A pyrimidine amino acid previously isolated from pea seedlings has been crystallised, and the tentative structure previously assigned has been reexamined by several chemical and physical techniques, including mass spectrometry and NMR spectrometry. 2. 2. Ultraviolet absorption spectra of the purified compound are more consistent with an N-1 substituted pyrimidine rather than the C-5 substituted structure previously suggested. Location of the side chain at N-1 was confirmed by NMR spectrometry which clearly reveals the presence of a pair of olefinic protons thus eliminating any possibility of substitution at C-4 or C-5. Chemical tests confirm the presence of an α-amino acid moiety. 3. 3. The free amino acid was insufficiently volatile for successful mass spectrometry but did show the characteristic fragment ions of uracil. The ethyl ester was prepared and its mass spectrum recorded. It shows a fragmentation pattern with features typical of both an N-1 substituted uracil and an α-amino acid ester. No parent ion could be detected but an accurate mass measurement on the base peak (m/e 154) is consistent with its expected structure as the amino fragment. 4. 4. The evidence presented demonstrates the structure to be that β-(2,6-dihydroxypyrimidin-1-yl) alanine. Infrared and mass spectrometric evidence shows that the amino acid occurs in the free form and not as a peptide as previously suggested. © 1969.