Revised structure of A53868A.

A53868A is a novel phosphorus-containing antibiotic obtained by fermentation of Streptomyces luridus NRRL15.101 ; the product has a broad-spectrum antimicrobial activity1^ The molecular formula of CnH22N3O5P(MW307) contains units of glycine, leucine, and C3H7NOSP ; mass spectral fragmentation observations and 1H NMRstudies were combined to suggest the structure 11}. However,attempts to synthesize a series of analogs of GLAPP (1) prompted a re-examination of the structure elucidation of the parent compound, A53868A. The pattern of carbonphosphorus coupling constants in the 13C NMR spectrum (see Table 1) requires that the structure of A53868A be revised to 2. The carbon-phosphorus coupling of 190.1 Hz indicates that phosphorus is directly bonded to the non-protonated carbon, while the two methylene carbons show only long-range coupling to the phosphorus10. Therefore, the propenyl-phosphonate fragment must have the structure 3 rather than 4.