N- -anthranilic acid

The following were administered separately to P. cyclopium [carboxyl- and [ N]-anthranilic acid, phenylalanine with labels at positions 1,2, and 3, and also N-labelled phenylalanine and [methyl- C]methiomne. The results show an intact incorporation of all the atoms of phenylalanine and anthranilic acid into both (49) and (50), with L-phenylalanine preferred over the D-isomer. The iV-methyl group originates from the S-methyl group of methionine. The cyclic dipeptide formed from these two amino-acids is presumably an intermediate on the pathway to the alkaloids. As phenylalanine serves as a precursor for cyclopenol, the origin of the hydroxy-group is by meta-hydroxylation of phenylalanine. Further, m-tyrosine and tyrosine are only unspecific precursors. 

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