CHEMICAL NATURE OF ANTIBIOTICS 



53 



Mutants of S. aureofacicKS, in chlorine- 

 containing media, can form another useful 

 \-ariation of the chlortetracycline molecule 

 t)y producing demethylchlortetracycline, in 

 which there is no metlwl group in position (i. 



Anhydrochlortetracycline is obtained l)y 

 acid degradation of chlortetracycline. It 

 differs from chlortetracycline in the structure 

 of rings B and C : 



CH 



OH () 



This compound has a rather specific activity 

 against actinomycetes (Goodman d al., 

 I'.l.'i.V). 



Antibicjtic X 340 is a tetracycline, the 

 complete structure of which is not yet 

 known. It differs in biological activity from 

 the other tetracyclines in that it is active 

 mainly against gram-posit i^'e bacteria. 



Acetylenic Compounds 



Two antibiotics, cellocidin and myco- 

 mycin, have acetylenic bonds. Cellocidin is 

 acetylenedicarboxamide, 



H,N— CO— C=C— CO— NHo 



It is active mainly against mycobact(>ria, 

 but also has a moderate action against l)ac- 

 teria. 



Mycomijcin has a wider range of anti- 

 microbial activity, being active against bac- 

 teria, mycobacteria, and fungi. It is an un- 

 saturated carb(«ylic acid with l)oth ethylenic 

 and acetylenic linkages: 



H=C— C=CCH=C=CHCH= 



CH— CH=CHCH,C( )()H 



This highly unstable substance explodes at 

 7o°C. A more stable and also biologically ac- 

 tive isomer is obtained by treatment of 



mycomycin with alkali. It is called isomyco- 

 mycin: 



CHsC^C- C=C— C=C— CH= 



CH— CH=CH— CH .— C( )OH 



Polyenic Compounds 



These unsaturated compounds have only 

 ethylenic bonds. They form a large group of 

 antibiotics which are mainly antifungal. 

 These polyenes can be grouped together on 

 the basis of the number of conjugated carbon 

 to carbon (loul)le l:)onds present in th(^ 

 molecule. Most of them have four, fi\e, six, 

 and seven such unsaturated bonds in their 

 chromophores which are responsible for \'ery 

 typical three-peaked light-absorption spec- 

 tra. One antibacterial antibiotic, antibiotic 

 PA 147, has a diene chromophore and could 

 be considered as a small polyene : 



f. ^OH 



H,C=CH 



O 



Antibiotic PA 147 has a lactone ring, like 

 the larger polyenes, but the polyenic portion 

 of the molecule is not all enclosed in the 

 lactone ring. 



The diene, antibiotic PA 147, has on(> 

 single peak of light absorption at 272 niju. 

 The polyenes with four conjugated double 

 bonds, the tetraenes, have three main peaks 

 of light absorption; the position of the 

 central peak is at 300 to 30o m/x. The posi- 

 tion of the central peak is 330 to 340 mn 

 for the pentaenes, 3oo to 3o9 m^i for the 

 hexaenes, and 377 to 388 ni/u for the hepta- 

 enes. To date, no triene or octaene has been 

 discovered among the products of actino- 

 mycetes. 



The complete structures of one tetraene, 

 pimaricin, and two pentaenes, filipin and 

 lagosin (Dhar et al., lUliO), have been re- 

 ported. Some headway has also been made 

 in the elucidation of the structures of the 

 tetraene nj^statin and of the heptaenes 



