Actions of Tryptophan Prenyltransferases Toward Fumiquinazolines and their Potential Application for the Generation of Prenylated Derivatives by Combining Chemical and Chemoenzymatic Syntheses

摘要

Dimethylallyltryptophan synthases (DMATSs) catalyze regiospecific transfer reactions of a prenyl moiety from dimethylallyl diphosphate to various positions of the indole ring of tryptophan. For example, FgaPT2, 5-DMATS, and 7-DMATS from Aspergillus fungi catalyze tryptophan prenylation at C-4, C-5, and C-7, while 5-DMATS(Sc) and 6-DMATS(Sa) from Streptomyces strains are tryptophan C-5 and C-6 prenyltransferases, respectively. In this study, our objective is to demonstrate the possibility of producing prenylated analogues of ardeemin fumiquinazoline (FQ) (1a), a precursor of the multidrug resistance (MDR) export pump inhibitor ardeemin, by using DMATSs. All ardeemin FQ stereoisomers were chemically synthesized and used as substrates for enzyme assays with DMATSs. Biochemical investigations revealed different features of these enzymes toward ardeemin FQ analogues, regarding activity and prenylation position. Isolation and structural elucidation showed that 7-DMATS catalyzed mainly regiospecific prenylation at C-7, which is also observed for its natural substrate l-tryptophan. Up to four prenylated derivatives were identified in the reaction mixtures of other enzymes. In total, 18 new prenylated ardeemin FQ analogues were obtained in this study. Molecular modelling of ardeemin FQ analogues with the crystal structure of FgaPT2 led to the identification of two potential amino acid residues for guidance of the prenylation position. The two generated mutants FgaPT2_M328L and FgaP-T2_Y398F showed significant prenylation shifts with 1a.