Showing papers by "Tomas Hudlicky published in 1998"

Chemoenzymatic Synthesis of All Four Stereoisomers of Sphingosine from Chlorobenzene: Glycosphingolipid Precursors1a

Abstract: Advantageous use of homochiral cyclohexadiene-cis-1,2-diol 2, available by means of biocatalytic oxidation of chlorobenzene with toluene dioxygenase, has enabled the synthesis of all four enantiomerically pure C18-sphingosines 1. The four requisite diastereomers of azido alcohols 4a−d were accessed by regioselective opening of epoxides 7 and 8 with either azide or halide ions. The configuration of C4 and C5 in azides 4 defines the stereochemistry of the incipient sphingosine chain, liberated from 4 by the oxidative cleavage of the C1−C6 olefin. For l-threo-sphingosine (1b), lactol 20b generated by this cleavage was converted by periodate oxidation to azido deoxy l-threose 22b, which gave 1b upon Wittig olefination and reduction. Similarly, d-erythro-sphingosine (1a) and l-erythro-sphingosine (1c) were generated from 4a,c, respectively. The last sphingosine (1d) was synthesized from the silyl-protected azido alcohol 29d. Subsequent transformations provided silyl-protected azido deoxy d-threose 32d, which u...

Inositol synthesis : concise preparation of l-chiro-inositol and muco-inositol from a common intermediate

Abstract: Fully stereoselective large-scale syntheses have been attained for l - chiro -inositol ( 2 ) and muco -inositol ( 3 ) by means of controlled peripheral oxygenation of cyclohexadiene diol 1 .

Natural Product Synthesis via Biocatalysis: An Essay on the Merits of Multidisciplinary Ventures

Abstract: A critical opinion is advanced on the merits of multidisciplinary ventures in synthetic organic chemistry In particular, the concept of a "tool box" of methodologies available for effective solutions to problems in organic synthesis is analyzed in the context of available examples from the literature as well as from the ongoing projects in our research group The discussion of several cases of recently accomplished total syntheses offers evidence that the introduction of biocatalytic methods greatly improves the overall process of preparation of target compounds Some examples of such projects form also the topic of the authors lecture at the 8th Brazilian Meeting on Organic Synthesis in September 1998

Chemoenzymatic and Electrochemical Oxidations in the Synthesis of Octahydroisoquinolines for Conversion to Morphine. Relative Merits of Radical vs. Acid-Catalyzed Cyclizations.

Abstract: Second-generation stereoselective synthesis of octahydroisoquinoline 3 , a potential key intermediate for the projected synthesis of the natural enantiomer of morphine, has been accomplished in five steps from arene cis -diol 8 . Electrochemical oxidation of 9b furnished 7b , a precursor for the key benzoate-assisted acyl0iminium cyclization.

New Metabolites from the Microbial Oxidation of Fluorinated Aromatic Compounds.

Abstract: m -Bromo-α,α,α-trifluorotoluene ( 1 ) and 1-bromo-2,3-difluorobenzene ( 4 ) were subjected to microbial oxidation by Pseudomonas putida strain 39/D and the corresponding Escherichia coli recombinant microorganism (strain JM 109(pDTG601)), which express toluene dioxygenase. The absolute stereochemistry of the major oxidation products have been determined as cis -(2 R ,3 S )-5-bromo-2,3-dihydroxy-α,α,α-trifluoromethylcyclohexa-4,6-diene ( 2 ), and cis -(2 S ,3 S )-1-bromo-5,6-difluoro-2,3-dihydroxy-4,6-diene ( 5 ). The regiochemistry of a minor metabolite has been established as cis -5-bromo-3,4-dihydroxy-α,α,α-trifluoromethylcyclohexa-1,5-diene ( 3 ).