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Sir: It was found in our laboratories that Streptomyces ,filvoviridis MC696-SY2 produced two Blactamase inhibitors1), designated as MC696SY2-A and B. They strongly inhibit B-lactamases, but are extremely unstable. This communication describes the isolation and structural study of MC696-SY2-A, one of the inhibitors, which allowed us to assign structure I. A broth filtrate was treated with Amberlite IRA-401 (SO4-form) and MC696-SY2-A (I) was eluted with 2 m ammonium chloride followed by adsorption on active carbon and elution with 50°. aqueous acetone. The ammonium salt was converted to a rather stable barium salt with Amberlite IR-120B (Ba++ form), affording brownish powder. The purification of the crude barium salt of I was achieved by the combination or repetition of column chromatography on ECTEOLA-cellulose, Diaion HP-20 (a macroreticular resin), Sephadex LH-20, Sephadex G-25, Florisil and silica gel. The sodium salt of I was obtained from the purified barium salt by treatment with Dowex 50W-X4 (Na+ form). It gave an ID50 to B-lactamase of Escherichia coli K-12 W3630R7, of 300 pg. l) The physical and chemical properties of the most purified barium and sodium salts of I are shown in Table 1. Although a tentative molecular formula was obtained for the salts, the content of oxygen remained ambiguously because of the difficulty of complete purification and unsuccessful preparation of the sample for a mass spectrum. However, the presence of O-sulfate or C-sulfonic acid was suggested from the IR spectrum and high-voltage paper electrophoresis. The barium salt of I was easily hydrolyzed to a non-B-lactam compound (II) even at room temperature. A partial structure CHs-CH-CH-

Isolation and structure of a .BETA.-lactamase inhibitor from Streptomyces.