4-amino-2-methyl-5-hydroxymethylpyrimidine 4-amino-2-methyl-5-pyrimidinemethanol 4-amino-5-hydroxymethyl-2-methylpyrimidine 6-amino-5-hydroxymethyl-2-methylpyrimidine 73-67-6 HMP Toxopyrimidine hydroxymethylpyrimidine pyramin pyramine