Enkastines: Amadori Products with a Specific Inhibiting Action against Endopeptidase - 24.11 - from Streptomyces albus and by Synthesis

Target‐oriented screening led to the detection of specific inhibitors of endopeptidase – EC 3.4.24.11 – (enkephalinase) in cultures of Streptomyces albus, ATCC 21 838. Isolation was performed by successive chromatographic methods and yielded enkastines in amounts of about 2 mg from 2000 kg of culture broth. Amino acid analysis, proton‐ and carbon‐NMR spectroscopy, mass spectrometry, and chemical degradation suggested the structure of the three most prominent enkastines to be N‐(1‐deoxyfructos‐1‐yl)‐isoleucyl‐aspartate (1), N‐(1‐deoxyfructos‐1‐yl)‐valyl‐aspartate (2), and N‐(1‐deoxyfructos‐1‐yl)‐valyl‐glutamate (3). This structural hypothesis was confirmed by chemical synthesis of the compounds according to the Amadori reaction of glucose with the corresponding dipeptides. The products turned out to be identical with the isolated material with respect to their NMR fingerprint (1H and 13C) and their biological properties. Enkastines are potent inhibitors of the endopeptidase 24.11. with IC50 of 1.8 × 10−9 M (1), 6.3 × 10−9 M (2) and 3 × 10−8 M (3). In contrast to phosphoramidon, a well‐known inhibitor of the enkephalinase, enkastines exhibit no activity against thermolysin. Kinetic studies characterize enkastine activity as competitively slow and tightly binding to endopeptidase – EC 3.4.24.11.