Cyclization of farnesyl diphosphate to pentalenene. Orthogonal stereochemistry in an enzyme-catalyzed S_E′ reaction

Abstract

Can. J. Chem. 72, 118 (1994). Pentalenene synthase catalyzes the cyclization of farnesyl diphosphate (1) to the sesquiterpene hydrocarbon pentalenene (4). Separate incubations of ( 4~, 8~) - [ 4 , 8 -~~~, 4,8-14~2]farnesyl diphosphate (la) and ( 4~, 8~) - [ 4 , 8 -~~~, 4,814~2]farnesyl diphosphate (lb) with pentalenene synthase isolated from Streptotnyces UC53 19 and analysis of the derived labeled pentalenenes, 4a and 4b, respectively, by chemical degradation established that H-8si of FPP was lost upon cyclization to pentalenene. Consideration of the plausible conformations of the enzymatic cyclization intermediates indicates that the electrophilic allylic additionelimination (SF,) reaction in which the C-4,5 bond of pentalenene is formed involves an orthogonal relationship between the C-C bond being formed and the C-H bond that is ultimately broken. (SE,). au cours de laquelle se forme la liaison C-4.5 du pentalknkne, implique une relation orthogonale entre la liaison C-C qui se forme et la liaison C-H qui sera finalement briste.[Traduit par la rCdaction]The formation of c a r b o n~a r b o n bonds by the electrophilic attack of carbenium ions on double bonds is one of the most important reactions in the biosynthesis of hundreds of isoprenoid metabolites, including linear polyprenols (dolichols, ubiquinones), cyclic terpenes (mono-, sesqui-, and diterpenes), and steroids and other triterpenes (cholesterol, a-amyrin) (I). Although this process has considerable precedent in solution phase chemistry and much is known about the physical organic chemistry of carbenium ions themselves, the enzymatic reactions remain poorly understood, both with respect to the means by which such reactive species are manipulated and stabilized by protein catalysts and the manner in which enzymes exercise regiochemical and stereochemical control over such reactions (2).One particularly important subclass of these electrophilic reactions involves the quenching of positive charge resulting from the initial addition to the double bond by the removal of one of the original allylic protons. This allylic addition%limi-nation formally corresponds to an SE process. Cornforth and Popjak have shown that the key chain elongation step of polyprenol biosynthesis, typified by the farnesyl diphosphate (FPP, 1) synthase reaction, involves a pair of net syn allylic additionelimination reactions (3). (Scheme I). By contrast, the closely analogous prototropic rearrangement of isopentenyl diphosphate (IPP, 2) to dimethylallyl diphosphate (DMAPP, 3) has been shown to occur with net anti stereochemistry (4). In more recent studies of the cyclization of farnesyl diphosphate (I) to the sesquiterpene hydrocarbon pentalenene (4), we have shown that theinitial SEl reaction takes place with net anti stereochemistry (5) (Scheme 2). Overton has described model experiments 'Dedicated with great affection and warm admiration to Professor Ian D. Spenser.2~u t h o r to whom correspondence may be addressed.in which an intramolecular SF reaction was shown to proceed...

Structural and Chemical Biology of Terpenoid Cyclases

“…350 − 354 The reaction is catalyzed by pentalenene synthase, and the isolation and purification of the enzyme from Streptomyces exfoliatus UC5319 enabled the study of isotopically labeled substrates to ascertain the molecular details of the catalytic mechanism. 347 , 355 − 357 Subsequent cloning and expression of the enzyme in E. coli yielded a fully functional recombinant enzyme identical in all respects to the native enzyme isolated from S. exfoliatus . 358 …”

Genome Mining in Streptomyces. Elucidation of the Role of Baeyer−Villiger Monooxygenases and Non-Heme Iron-Dependent Dehydrogenase/Oxygenases in the Final Steps of the Biosynthesis of Pentalenolactone and Neopentalenolactone

“…Pentalenene synthase, which catalyzes the cyclization of farnesyl diphosphate ( 2 , FPP) to the parent sesquiterpene hydrocarbon pentalenene ( 3 ) (32), has been cloned from S. exfoliatus UC5319 and expressed in Escherichia coli (33) and its crystal structure has been determined (34). The detailed mechanism and stereochemistry of the cyclization itself has been elucidated (31, 35). In addition, a variety of oxidized metabolites that represent plausible intermediates and shunt metabolites in the conversion of pentalenene to pentalenolactone have been isolated from several pentalenolactone-producing strains of Streptomyces (36–40).…”

Incorporation of deuterium-labelled analogs of isopentenyl diphosphate for the elucidation of the stereochemistry of rubber biosynthesis

“…Substrates 6, 23 7, 23 and 8 24 were prepared as described previously. The synthesis of (S)-[2-2 H 1 ]-IPP 9 is analogous to 8 and is shown in Scheme 3.…”