497 



Pyrazines, Diketopiperazines 



from leucine, the echinulin moiety from leucine and ala- 

 nine, aspergillic acid from leucine and isoleucine, the 

 mvcelianamide moiety from tyrosine and alanine, picroro- 

 cellin from phenylalanine, and gliotoxin from phenyl- 

 alanine and serine. It might be mentioned that we have 

 isolated from a Rhizopus nigricans culture a diketopipera- 

 zine which is a derivative of isoleucine and valine (un- 

 published). 



Dehydration, dehydrogenation, oxidation and N- or 

 O-methylation sometimes occur to obscure the origin to 

 some degree. Aromatization to a pyrazine has taken place 

 in flavacol and pulcherriminic acid, aspergillic acid, a 

 dihydropyrazine, representing an intermediate oxidation 

 state. Formation of pulcherriminic acid might be repre- 

 sented as follows: 



OH H2N 



CH3 



CH3 



\ 



CH— CH2— CH 



I \ 



CH— CH2— CH C= O CH3 



/ \ / 



CH3 NH2 HO 



H 



-H2O 



CH3 



CH3 



\ 



O [\ CH3 



CH3 C CH— CH2— CH H2O 



\ II \ — 



CH— CH2— CH C=0 CH3 



/ \ \ 



CH3 NH2 OH 



CH3 "— 



CH— CH2— CH 



CH— CH2— CH C=0 

 H 



CH3 



CH3 



CH3 



\ 



HO— C C— CH2— CH — H2 



CH3 



CH— CH2 



C C— OH 



H 



CH3 



