Unusual nonprotein imino acid and its relationship to phenolic and nitrogenous compounds in Copaifera

The unusual imino acid, N-methyl-trans-4-hydroxy-Lproline has been isolated from leaves of five species of the leguminous tropical tree Copaifera, and for the first time characterized by ¹H and ¹³C NMR and mass spectrometry. This imino acid can constitute up to 3% of the mature leaf dry weight and 10% of the nitrogen; it also constitutes 2–3 % of the dry weight of the seed. Preliminary feeding trials have shown it to be a very effective inhibitor of larval development of the seed-feeding bruchid beetle Callosobruchus maculatus and to have significant feeding deterrence of the leaf-feeding lepidopteran Spodoptera littoralis. Phenolic compounds, also known to affect herbivores adversely, comprise 6–10% leaf dry weight. However, the imino acid displayed a mean of 50% reactivity compared to standards commonly used in analysis of total phenolics by the Folin-Denis (F-D) assay [gallic acid, tannic acid and (+) catechin], thus resulting in a significant overestimate of phenolics by this assay. It is concluded that assessment of leaf food quality for herbivores of Copaifera by assays widely used for this purpose in ecological studies, such as F-D for phenolics and Kjeldahl for total nitrogen content, give some misleading results.