The structures of two new, naturally occurring p-lactams are proposed on the basis of spectroscopic properties, and their interconversion.RECEXT reports have described the structures of clavulanic acid (1)l and thienamycin (2) ,2 two naturally occurring /3-lactams with novel, bicyclic ring systems. We now describe the spectroscopic evidence to support structures (3) and (8) for MM 13902 and MM 4550, two new p-lactam antibiotics isolated from Streptoinyces o l i ~a c e u s . ~ The derivative MM 13902 was isolated as the freezedried disodium salt (4),$ Cl,Hl,N2Na,0,S2, which had the following properties: [cc];bo -81" (c 1.0 in H,O); Vmax (KBr) 1750 (p-lactam CO), 1675 (amide CO), 1620br (C0,-), and 1220-1270br (OSO,-) cm-l; A, , , (H,O) 307 ( E 15,520) and 227 (14,650) nm. The lH n.m.r. spectrum in D20 (rel. to internal standard MeCN, 6 2-00) revealed thirteen of the protons ; the smide proton exchanged under these conditions. f We shall refer to structure (A) (see end of text) as olivanic acid. g y C H 2 0 H H O ) -q -sc H ,C" * NH * 0 f Me $ The empirical formula was obtained by elemental analysis of several crystalline monoester derivatives and mass spectral studies on the dimethyl ester.

The structure of the olivanic acid derivative (1) IN an earlier communication1 we described the spectroscopic has been confirmed by a novel ,&lactam degradation in data to support structures (1) and (2) for two new, /3dimethyl sulphoxide ; application of this reaction has lactam antibiotics isolated from Streptomyces olivaceus. resulted in the structure elucidation of a new antibiotic, We now report a novel transformation which confirms MM 17880.structure (1) and which enabled us to elucidate the structure (12) of a closely related, co-occurring metabolite, MM 17880.a

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Sunzmary Lead tetra-acetate attacks (3R : 4R)-l-( 1-p-A RECENT report1 described certain non-fused p-lactams methoxybenzyloxycarbonyl-2-methylprop-1-enyl) -4-obtained via a novel cleavage of the 1,2-bond of 6-tritylmethylthio-3-(phenoxyacetamido) azetidin-2-one (I) a t aminopenicillanates. Although these 1,2-seco-penicillins the sulphur atom and the adjacent carbon atoms, where-[e.g. (I) and the corresponding acid] have no significant as osmium tetroxide and potassium permanganate antibacterial activity, they could prove valuable as interremove the complete substituent from the p-lactam mediates for new fused ,&lactams which might be active. nitrogen of (I) and other 1,2-seco-penicillins.A possible first step in such a scheme would be the intro-