The mechanism of the acid-catalyzed decomposition of the farnesyl phosphates

Enantioselective Tail-to-Head Cyclizations Catalyzed by Dual-Hydrogen-Bond Donors

Chiral urea derivatives are shown to catalyze enantioselective tail-to-head cyclization reactions of neryl chloride analogues. Experimental data are consistent with a mechanism in which π-participation by the nucleophilic olefin facilitates chloride ionization and thereby circumvents simple elimination pathways. Kinetic and computational studies support a cooperative mode of catalysis wherein two molecules of the urea catalyst engage the substrate and induce enantioselectivity through selective transition state stabilization.

Convenient methods for the synthesis of P1-farnesyl-P2-indicator diphosphates

To access P1-farnesyl-P2-indicator diphosphates, more efficient methods for the synthesis of farnesyl-phosphate and diphosphates were developed. The procedures reported here provide more flexible conditions than the conventional imidazolide and morpholidate coupling methods. Milder conditions for the synthesis of sensitive allylic diphosphates and greatly improved reaction efficiencies provide access to novel reagents for analysis of diphosphate-based enzymatic reactions.

Efficient one-step syntheses of isoprenoid conjugates of nucleoside 5'-diphosphates

[reaction: see text] Isoprenoid conjugates of nucleoside 5'-diphosphates were efficiently synthesized by one-step nucleophilic displacement reactions of either isoprenyl chlorides or isopentenyl tosylate with nucleoside 5'-diphosphates.

Polyprenyl phosphates: synthesis and structure-activity relationship for a biosynthetic system of Salmonella anatum O-specific polysaccharide

A series of polyprenyl phosphates with modified structure of polyprenyl residue was prepared through phosphorylation of polyprenyl trichloroacetimidates with phosphoric acid. Interaction of polyprenols with tetra-n-butylammonium dihydrogen phosphate and trichloroacetonitrile was found to represent a very efficient, simple and general method for the synthesis of polyprenyl phosphates. A procedure was developed for smooth conversion of polyprenyl pyrophosphates into the monophosphates through hydrolysis in the presence of 4-dimethylaminopyridine. The polyprenyl phosphates prepared were studied as substrates for the enzymes of Salmonella anatum O-specific polysaccharide biosynthesis. Correct stereochemistry of alpha- and beta-isoprenic units was found to be essential for substrate efficiency. At the more remote positions of the hydrocarbon chain just the presence of isoprenic units of any configuration seems necessary. Some changes in position of the phosphate group may be permissible without significant loss of substrate properties.

Isotopically sensitive branching in the formation of cyclic monoterpenes: proof that (-)-alpha-pinene and (-)-beta-pinene are synthesized by the same monoterpene cyclase via deprotonation of a common intermediate

To determine whether the bicyclic monoterpene olefins (-)-alpha-pinene and (-)-beta-pinene arise biosynthetically from the same monoterpene cyclase by alternate deprotonations of a common carbocationic intermediate, the product distributions arising from the acyclic precursor [10-2H3,1-3H]geranyl pyrophosphate were compared with those resulting from incubation of [1-3H]geranyl pyrophosphate with (-)-pinene cyclase from Salvia officinalis. Alteration in proportions of the olefinic products generated by the partially purified pinene cyclase resulted from the suppression of the formation of (-)-beta-pinene (C10 deprotonation) by a primary deuterium isotope effect with a compensating stimulation of the formation of (-)-alpha-pinene (C4 deprotonation). (-)-Pinene cyclase as well as (+)-pinene cyclase also exhibited a decrease in the proportion of the acyclic olefin myrcene generated from the deuteriated substrate, accompanied by a corresponding increase in the commitment to cyclized products. The observation of isotopically sensitive branching, in conjunction with quantitation of the magnitude of the secondary deuterium isotope effect on the overall rate of product formation by the (+)- and (-)-pinene cyclases as well as two other monoterpene cyclases from the same tissue, supports the biosynthetic origin of (-)-alpha-pinene and (-)-beta-pinene by alternative deprotonations of a common enzymatic intermediate. A biogenetic scheme consistent with these results is presented, and alternate proposals for the origin of the pinenes are addressed.