Biosynthetic origin of hydrogen atoms in the lipase inhibitor lipstatin.
The lipase inhibitor lipstatin is biosynthesized in Streptomyces toxytricini via condensation of a C(14) precursor and a C(8) precursor, which are both obtained from fatty acid catabolism. To study the mechanism of this reaction in more detail, S. toxytricini was grown in medium containing a mixture of U-(13)C,U-(2)H-lipids and unlabeled sunflower oil or in a medium containing 70% D(2)O. Lipstatin was isolated and analyzed by (1)H,(2)H, and (13)C NMR spectroscopy. Hydrogen atoms at C-2, C-3, and C-4 of lipstatin were found to be derived from solvent protons. The formation of the lipstatin precursor 3-hydroxy-Delta(5,8)-tetradecadienoyl-CoA by beta oxidation of linoleic acid explains the incorporation of solvent hydrogen into the 4 position of lipstatin. The hydrogen in position 3 of lipstatin is most probably introduced from solvent by proton/deuterium exchange of a redox cofactor involved in the reduction of the keto group in the branched chain beta keto acid arising by a decarboxylative condensation. The incorporation of solvent hydrogen at position 2 can be explained by epimerization of a chiral intermediate at C-2 and C-3. Epimerization may involve a dehydration-rehydration mechanism.
Goese
M
M
Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
Eisenreich
W
W
Kupfer
E
E
Weber
W
W
Bacher
A
A
D002247:Carbon Isotopes; D003903:Deuterium; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D006368:Helianthus; D006859:Hydrogen; D007783:Lactones / Q000737:chemistry* / Q000378:metabolism*; D008049:Lipase / Q000037:antagonists & inhibitors; D050356:Lipid Metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010938:Plant Oils / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D013302:Streptomyces / Q000378:metabolism*; D000074242:Sunflower Oil
D002247:Carbon Isotopes; D004791:Enzyme Inhibitors; D007783:Lactones; D010938:Plant Oils; D000074242:Sunflower Oil; D006859:Hydrogen; C054164:lipstatin; D003903:Deuterium; D008049:Lipase