A problem in the structure assignment of acremolin C, which is most probably identical with acremolin B.

With the help of chemical shifts computed with density functional theory (DFT), it is demonstrated that the reported experimental 13 C NMR data of acremolin C are incompatible with the claimed structure of an N2 ,3-ethenoguanine with an isopropyl group at C-1'. An alternative structure, which is in agreement with both experimental and computed data, presents an isopropyl group at the C-2' position of an N2 ,3-ethenoguanine and leads to the conclusion that acremolin C is identical with acremolin B.