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UBC Theses and Dissertations

Indole prenyltransferases : mechanistic studies and inhibitor design Mahmoodi, Niusha


The cyclic dipeptide N-prenyltransferase (CdpNPT) catalyzes the reverse C-3 prenylation of a variety of cyclic dipeptides and benzodiazepinediones. A previous study misassigned the structure of the product of this reaction. In this work, the true product of the CdpNPT-catalyzed reaction between cyclo-L-Trp-L-Trp and dimethylallyl diphosphate (DMAPP) is identified as a C-3 reverse prenylated species. Furthermore, the non-enzymatic Cope/aza-Cope rearrangement of the CdpNPT product was examined under acidic conditions. Our results indicated that only the aza-Cope rearrangement onto the N-1 position of the indole ring can occur and no Cope rearrangement onto the C-4 position was observed. These results suggest that in the absence of an enzyme active site, the aza-Cope rearrangement is preferred over the Cope rearrangement. Brevianamide F prenyltransferase (FtmPT1) catalyzes the C-2 normal prenylation of brevianamide F (cyclo-L-Trp-L-Pro). A mechanism involving a direct C-2 attack was proposed for this reaction. However, the structural analysis of FtmPT1, as well as studies of alternate substrates and mutant enzymes suggested that a different mechanism involving an initial C-3 reverse prenylation followed by a rearrangement may be operative. In this work, we investigated the reactivity of FtmPT1 with tryptophan and cyclo-L-Trp-L-Trp, as well as two alternate substrates: 5-hydroxybrevianamide F and 2-methylbrevianamide F. The isolated products were reverse prenylated at C-3 and normal prenylated at N-1, C-2, C-3, or C-4. The formation of these products can be rationalized through mechanisms involving either an initial C-3 normal or C-3 reverse prenylation as the first step of catalysis. 4-Dimethylallyltryptophan synthase is an aromatic prenyltransferase that catalyzes an electrophilic aromatic substitution reaction between DMAPP and L-tryptophan. The reaction is believed to proceed via the dissociation of DMAPP to form a dimethylallyl cation/phosphate ion pair. An inhibitor containing a guanidinium moiety appended to a phosphorylated phosphonate was designed in order to mimic the transition state for the dissociation of DMAPP into an allylic carbocation and pyrophosphate. This compound was found to serve as a potent competitive inhibitor (submicromolar Ki value) of the enzyme 4-DMATS.

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