(8) The A334 location for the double bond in the diketopiperazine reported by Bundgaard7 (4) is incorrect. It is apparent from an examination of the NMR spectrum of this compound that the doublet at 6 1.2 with J= 7 Hz is indicative of a methyl function at C3 adjacent to one hydrogen. One would expect the methyl at C3 in a A384 compound to have 6-2.0 and Jn 0 Hz as in cephalexin. The correct structure for the diketo iperazine is 3b, analogous to the ...
