David C. Myles

Yeast and Rat Coq3 and Escherichia coli UbiG Polypeptides Catalyze Both O-Methyltransferase Steps in Coenzyme Q Biosynthesis*

Ubiquinone (coenzyme Q or Q) is a lipid that functions in the electron transport chain in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. Q-deficient mutants of Saccharomyces cerevisiae harbor defects in one of eight COQ genes (coq1–coq8) and are unable to grow on nonfermentable carbon sources. The biosynthesis of Q involves two separate O-methylation steps. In yeast, the first O-methylation utilizes 3,4-dihydroxy-5-hexaprenylbenzoic acid as a substrate and is thought to be catalyzed by Coq3p, a 32.7-kDa protein that is 40% identical to theEscherichia coli O-methyltransferase, UbiG. In this study, farnesylated analogs corresponding to the secondO-methylation step, demethyl-Q3 and Q3, have been chemically synthesized and used to study Q biosynthesis in yeast mitochondria in vitro. Both yeast and rat Coq3p recognize the demethyl-Q3 precursor as a substrate. In addition, E. coli UbiGp was purified and found to catalyze both O-methylation steps. Futhermore, antibodies to yeast Coq3p were used to determine that the Coq3 polypeptide is peripherally associated with the matrix-side of the inner membrane of yeast mitochondria. The results indicate that oneO-methyltransferase catalyzes both steps in Q biosynthesis in eukaryotes and prokaryotes and that Q biosynthesis is carried out within the matrix compartment of yeast mitochondria.

THE KINETICS AND THERMODYNAMICS OF BICYCLIC KETAL FORMATION : AN APPLICATION TO THE SYNTHESIS OF THE ZARAGOZIC ACIDS

Abstract The kinetics and thermodynamics of ketalization of tetrahydroxyketones are examined in the synthesis of the ketal core of zaragozic acid Bx3.

1. SYNTHESIS OF THE COMMON C.1-C.13 HYDROPHOBIC DOMAIN OF THE B-TYPE AMPHIDINOLIDES

Abstract In this letter, the first of two in this issue, we describe the synthesis of the C.1–C.13 hydrophobic domain common to the B-type amphidinolides.

2. Synthesis of the C.14–C.26 hydrophilic domain of amphidinolide B1 and formation of the (E)-1,1′,3-trisubstituted diene sector

Abstract In the preceding letter, we described a synthesis of the conserved C.1–C.13 hydrophobic domain common to the potent B-type amphidinolides. In this letter, we present syntheses of the C.14–C.26 hydrophilic domain specific to amphidinolide B1 and a model for uniting the hydrophobic and hydrophilic domains to form the ( E )-1,1′,3-trisubstituted diene.

The biosynthesis of ubiquinone: Synthesis and enzymatic modification of biosynthetic precursors

Abstract The synthesis of key intermediates in the eukaryotic biosynthetic pathway of ubiquinone (Q) and the biotransformation of these materials with yeast ( S. cerevisiae ) mitochondria are described. The synthesis of Q aromatic precursors 2,3 , and 4 (n = 3 in all cases) relies on the palladium (O) catalyzed coupling of farnesyl tributylstannane with suitably functionalized aryl halides. Preliminary experiments show that incubation of synthetic substrate 3 with mitochondria from yeast containing the 3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase gene ( COQ3 ) and S-[ methyl - 3 H]adenosyl-L-methionine yields radiolabeled 4 .

The synthesis of the C-9 to C-21 sector of discodermolide: An efficient route to the C13–14 Z-trisubstituted alkene

Abstract The synthesis of the C-9 to C-21 sector of the immunosuppressive marine natural product discodermolide is described. The C-9 to C-15 subunit is synthesized in five steps from aldehyde 5 using the diene aldehyde cyclocondensation reaction. Diastereoselective alkylation of the previously synthesized C-16 to C-21 subunit by a suitably functionalized C-9 to C-15 synthon ( 3 ) leads to the C-9 to C-21 sector of discodermolide.

The synthesis of the Zaragozic acids: Equilibrium control of stereochemistry in the dioxabicyclo[3.2.1]octane core

Abstract The synthesis of the core of zaragozic acid Bx3 and a general strategy for the synthesis of the dioxabicyclo[3.2.1]octane core of the zaragozic acids is described.

An alkylative strategy to the C-13 to C-21 sector of discodermolide

Abstract An approach to the C-13 to C-21 sector of the immunosuppressive marine natural product discodermolide (1) is described. The C-15 to C-16 bond is formed by diastereoselective alkylation of a ketone enolate. Either diastereomer of alkylation can be obtained by selecting the appropriate counter ion. The C-16 to C-21 subunit is prepared in two steps from 11.

Progress toward the synthesis of a biomimetic membrane

Abstract Ubiquinone has antioxidant properties and is important in the conversion of products from glycolysis and the citric acid cycle to ATP. We report the synthesis of the necessary components of a biological membrane mimic that can serve as a model system for elucidating the third step in the prokaryotic biosynthesis of ubiquinone.

An Improved Procedure for the Preparation of the O,2-Dianion of Allyl Alcohol

Abstract An improved procedure for the preparation of the O,2-dianion of allyl alcohol is described. The use of the magnesium alkoxide of 2-bromopropen-1-ol instead of the known lithium salt, suppresses dehydrohalogenation upon treatment with tert-butyl lithium and furnishes the dianion. Addition of this dianion to a variety of carbonyl compounds affords the expected products in good yield.