Fellutanine
Fellutanine A, B, C and D are bio-active diketopiperazine alkaloids isolated from the cultures of Penicillium fellutanum, that belongs to a class of naturally occurring 2,5-diketopiperazines. Originally they were thought to be based on the "trans" cyclic dipetide cyclo but were later shown to be based on the "cis" cyclic dipetide cyclo. This was also confirmed when fellutanine A, B and C were isolated from Penicillium simplicissimum. The fellutanines A−C, are non-annulated analogues of cyclo, but unlike their diannulated analogue fellutanine D are not cytotoxic.