Toxin molecule, probable structure

A weakly neurotoxic metabolite, neoxaline (58) 107), mp 202°C (dec.), —16.3° (CHCI3), is described here even though it does not possess a diketopiperazine system in the molecule. It was isolated from cultures of Asp. japonicus (yield, 230 mg/18 liters) (see this treatise, Vol. 22 (1984), p. 317) 108). Its physicochemical properties are very similar to oxaline (59), isolated from Pen. oxalicum, and the unique structure was determined by correlation with oxaline (709). The efficient conversion of roquefortine (60) to oxaline (24.3%) is known (770), and neoxaline is probably also biosynthesized from 60, which has been isolated from Pen. roquefortii 111) as a tremorgenic toxin and has a tryptophan-histidine-derived diketopiperazine system in the molecule. 

The structure of the final complex, predicted by computer modelling, is presented in Fig. 10. This complex contains one molecule of Microcystin-LR, one molecule of AMPSA and six molecules of UAEE. The same molar ratio predicted by the modeling program was then used for the synthesis of the polymer. Two of the four monomers selected for the annealing process were unable to establish direct binding with the toxin, probably due to steric factors and internal competition (the monomers favored interaction with one another rather than with Microcystin-LR). 

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