Tritritionikkomycin Z, [uracil-5-3H,pyridyl-2,4-3H2]: Radiolabeling of a potent inhibitor of fungal and insect chitin synthetase

Nikkomycin Z (NZ) (a potent fungicide, insecticide, miticide, and inhibitor of fungal and insect chitin synthetase) was converted to a mixture of specific mono-, di-, and tribromo derivatives (BrNZ, Br2NZ, and Br3NZ, respectively) on reaction with N-bromosuccinimide in N,N-dimethylformamide. Substitution by bromine occurred first at the 2-position of the 3-hydroxypyridyl moiety, second at the 5-position of the uracil moiety, and finally at the 4-position of the 3-hydroxypyridyl moiety as observed both for NZ and for mixtures of uridine and 3-hydroxy-6-methylpyridine as model compounds representative of the moieties of NZ. Following fractionation of the various bromonikkomycin derivatives by HPLC, their structures were assigned by NMR, MS, and UV analyses. Catalytic reductive debromination of Br3NZ with tritium gas over palladium on carbon gave [uracil-5-3H,pyridyl-2,4-3H2]NZ. This material has sufficiently high specific activity (∼60 Ci/mmol) and suitable positions of labeling to study its uptake, distribution, metabolism, and possible target site interactions in fungal and insect systems