552298-24-5Relevant academic research and scientific papers
Mechanism and stereospecificity of a fully saturating polyketide synthase module: Nanchangmycin synthase module 2 and its dehydratase domain
Guo, Xun,Liu, Tiangang,Valenzano, Chiara R.,Deng, Zixin,Cane, David E.
supporting information; experimental part, p. 14694 - 14696 (2011/01/07)
Recombinant nanchangmycin synthase module 2 (NANS module 2), with the thioesterase domain from the 6-deoxyerythronolide B synthase (DEBS TE) appended to the C-terminus, was cloned and expressed in Escherichia coli. Incubation of NANS module 2+TE with (±)-2-methyl-3-keto-butyryl-N-acetylcysteamine thioester (1), the SNAC analog of the natural ACP-bound substrate, with methylmalonyl-CoA (MM-CoA) in the absence of NADPH gave 3,5,6-trimethyl-4- hydroxypyrone (2), identified by direct comparison with synthetic 2 by radio-TLC-phosphorimaging and LC-ESI(+)-MS-MS. The reaction showed k cat 0.5 ± 0.1 min-1 and Km(1) 19 ± 5 mM at 0.5 mM MM-CoA and kcat(app) 0.26 ± 0.02 min-1 and Km(MM-CoA) 0.11 ± 0.02 mM at 8 mM 1. Incubation in the presence of NADPH generated the fully saturated triketide chain elongation product as a 5:3 mixture of (2S,4R)-2,4-dimethyl-5-ketohexanoic acid (3a) and the diastereomeric (2S,4S)-3b. The structure and stereochemistry of each product was established by comparison with synthetic 3a and 3b by a combination of radio-TLC-phosphorimaging and LC-ESI(-)-MS-MS, as well as chiral capillary GC-MS analysis of the corresponding methyl esters 3a-Me and 3b-Me. The recombinant dehydratase domain from NANS module 2, NANS DH2, was shown to catalyze the formation of an (E)-double bond by syn-dehydration of the ACP-bound substrate anti-(2R,3R,4S,5R)-2,4-dimethyl-3,5-dihydroxyheptanoyl-ACP6 (4), generated in situ by incubation of (2S,3R)-2-methyl-3-hydroxypentanoyl-SNAC (5), methylmalonyl-CoA, and NADPH with the recombinant [KS6][AT6] didomain and ACP6 from DEBS module 6 along with the ketoreductase from the tylactone synthase module 1 (TYLS KR1). These results also indirectly establish the stereochemistry of the reactions catalyzed by the KR and enoylreductase (ER) domains of NANS module 2.
Synthetic studies on borrelidin: enantioselective synthesis of the C1-C12 fragment.
Vong, Binh G,Abraham, Sunny,Xiang, Alan X,Theodorakis, Emmanuel A
, p. 1617 - 1620 (2007/10/03)
[structure: see text] An efficient, enantioselective synthesis of the C1-C12 fragment 2 of borrelidin is presented. Construction of the "skipped" polymethylene chain of 2 was accomplished by iteration of Myers' alkylation, while formation of the C3 stereocenter was achieved by Roush's asymmetric allylboration methodology.
