Synthesis of 4-Methylene-DL-proline: a Naturally Occurring Racemic Amino-acid

ROTATIONAL and other data from the synthesis of an optically active derivative 1 have shown that 4-methylene-proline (I) isolated under non-epimerizing conditions from loquat seeds 2 is racemic. The suspected biogenetic precursor, γ-methyleneglutamic acid, on the other hand, has been found only in optically active form 3 , although in different plant sources 4 . In view of the rare occurrence of racemic amino-acids in Nature we wish to record the following simple synthesis of 4-methylene- DL -proline, along with direct comparison evidence confirming its identity with the natural compound.