https://123dok.net/document/nq775noq-stability-of-d-5-5-dimethyl-delta2-thiazoline-4-carboxylic-acid-in-relation-to-its-possible-occurrence-as-a-degradation-product-of-penicillin-by-the-exocellular-dd-carboxypeptidase-transpeptidase-from-streptomyces-r61-and-the-membrane-bound-dd-carboxypept.html