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The carbon skeleton of the polyether antibiotic lC1139603 (1) is shown to consist of a polyketide chain, derived from seven acetate units and six propionate units, combined with a &-unit of unknown origin.

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A new approach to volume-selected in vivo NMR spectroscopy uses two frequency-shifted sinc pulses, in conjunction with pulsed field gradients, to destroy the coherence of the unwanted signals. A hard pi/2 pulse can then be used to read the z magnetization in the region of interest. This method is independent of T2, provides complete volume selection in a single acquisition, and can be readily implemented on most high-field commercial imaging/spectroscopy systems.