STRUCTURE OF CUCURBITINE

Cucurbitine (C₅H₁₀O₂N₂), an amino acid effective against Schistosomiasis japonica which was isolated from the seeds of Cucurbita moschata Duch., was studied by chemical degradation. Cucurbitine was shown to contain one primary and one secondary amino group, and one carboxyl group. When it was heated with ninhydrin in the presence of citric buffer (pH 2.5), carbon dioxide was evolved quantitatively, the concomittant evolution of ammonia was incomplete but constant. Tests for unsaturated double bond, C-methyl group and N-methyl group gave negative results. N-Monotosyl derivative (Ⅲ) was prepared, which gave (Ⅴ) when oxidized with sodium hypobromite. An intermediate oxidative product was isolated and characterized as the bromo-imine (Ⅳ). Compound (Ⅴ) showed ketonic characteristics, with a sharp IR band at 5.69μ, hence should be cyclic and five-membered. When compound (Ⅴ) was oxidized according to the method of Baeyer and Villiger, formaldehyde and N-tosyl-β-alanine (Ⅵ) were obtained. The melting point of the product (Ⅵ) showed no depression when admixed with an authentic sample, and their IR spectra were identical. Since compound (Ⅵ) corresponded to only one carbon atom less than (Ⅴ), the bonds must be broken by the following way: Therefore compound (Ⅴ) should possess the formula as shown above, and cucurbitine is beyond reasonable doubt β-amino-β-carboxylpyrrolidine.