180 CARBON METABOLISM III 



are reviewed by Raistrick (430). As mentioned earlier, the effects of 

 metals on patulin production indicate that it is biosynthetically related 

 to some of the aromatic compounds of fungi. 



Alternariol is a dibenzo-l,2-pyrone formed by Alternaria tenuis 

 after long-continued growth on a glucose medium (435). There is no 

 reason to believe that it is metabolically related to the 1,4-pyrones. 



5. DERIVATIVES OF FURAN 



A number of fungal metabolites are structurally furan derivatives. 

 Most of these are derivatives of tetronic acid and have in common the 

 structure: 



HO— C=C— Rj 



! I 



r 2 — G C=0 



\ / 



o 



One organism, Penicillium charlesii, forms five related compounds of 

 this type: y-methyltetronic acid, carlic acid, carlosic acid, carolinic 

 acid, and carolic acid (140, 143). Other compounds of the same 

 general class are terrestric acid of Penicillium terrestre (82), dehydro- 

 carolic acid of P. cinerascens (94), and penicillic acid of Penicillium 

 spp. and Aspergillus spp. (6, 78, 227). 



L-Ascorbic acid, well known as a product of higher plants, has been 

 isolated from the culture filtrate of Aspergillus niger (223). Its rela- 

 tion to the tetronic acids is shown by its structure: 



HO— C G— OH 



I I 



CHoOH— CHOH— C C=0 



\ / 



O 



Ascorbic acid 



Studies on higher plants indicate that ascorbic acid is synthesized from 

 glucose without rupture of the carbon chain and that L-galactono-y- 

 lactone is an important intermediate (367). It is also striking, in view 

 of the formation of oxalic acid by Aspergillus niger, that oxalic acid is 

 an end product of ascorbate metabolism in the guinea pig (99). Re- 

 ports of ascorbic acid in fungi other than Aspergillus niger are sum- 

 marized by Van Lanen and Tanner (531). 



An ascorbic acid oxidase of the higher plant type, containing cop- 

 per, has not been reported from fungi. Myrothecium verrucaria 



