6 Essays in Biochemistry 



that it might contain an unsaturated lactone ring, which underwent 

 hydrogenolysis on catalytic reduction to yield the reduced deoxy acid. 

 Since it underwent a rearrangement strikingly similar to the myco- 

 mycin to isomycomycin isomerization and since the product, nemotin 

 A, also yielded undecanoic acid on reduction, it was further postulated 

 that nemotin, like mycomycin, contained an allene grouping which was 

 isomerized to an acetylenic linkage on treatment with alkali. These 

 two postulates proved to be partially correct, since a lactone ring and 

 an allenic system have been demonstrated by Bu'Lock, Jones, and 

 Leeming. 31 On the basis of the mycomycin-isomycomycin isomeriza- 

 tion, which involves a shift of bonds as well as an allene-acetylene 

 shift, the conversion might be pictured as follows: 



HC=C— C=C— C=C=C— C=C— C— C=0 vi 



o 



H 3 C— GheeC— c^c— C^C— C=C— C— COOH ViiiV=°hJ 



The hydroxyl might be lost on reduction of nemotin A 32> 33 or during 

 the conversion of VI to VIII. The acid VIII was synthesized by F. 

 Bohlmann 34 who very kindly sent us a sample for comparison with 

 nemotin A. This compound proved to have less antibiotic activity than 

 nemotin A against a number of bacteria and fungi and to have an 

 ultraviolet spectrum in which the maxima, as compared to those of 

 nemotin A, were shifted consistently 2 to 3 m/i, toward higher wave- 

 lengths (Fig. 1). The explanation for both of these differences has 

 been provided by the findings of Bu'Lock, Jones, and Leeming, who 

 have demonstrated the conversion to be: 



HC^C— C=C— C=C=C— C— C— C— C=0 IX Nemotin 



O 

 HC=C— C=C— C=C— C=C— C— C— COOH X Nemotin A 



That is, nemotin contains a saturated lactone ring, which opens on 

 alkali treatment, with loss of water, providing a new double bond. No 

 shift of acetylenic bonds occurs, only an allene to acetylene shift. The 

 fact that nemotin A (X), as opposed to Bohlmann's acid (VIII), 

 contains a terminal acetylenic carbon atom presumably accounts for 



