Neutron Diffraction Structure of (2R,3R)-L-(-)-[2-D]Carnitine Tetrachloroaurate, [(CH3)3N-CH2-CHOH-CHD-COOH]+[AuCl

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• 作者：Robert Bau ; André ; Schreiber ; Tobias Metzenthin ; Roy S. Lu ; Frank Lutz ; Wim T. Klooster ; Thomas F. Koetzle ; Hermann Seim ; Hans-Peter Kleber ; Fred Brewer ; and Sasha Englard
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：December 17, 1997
• 年：1997
• 卷：119
• 期：50
• 页码：12055 - 12060
• 全文大小：237K
• 年卷期：v.119,no.50(December 17, 1997)
• ISSN：1520-5126

文摘

Single-crystal neutron diffraction has been used to determine thestereochemical course of the hydrationof trans-crotonobetaine to L-(-)-carnitine bythe enzyme L-carnitine dehydratase. Firstly, an X-rayanalysis of theundeuterated carnitinium salt[(CH₃)₃N-CH₂-CH(OH)-CH₂-COOH]⁺[AuCl₄]^-confirmed that the absolute configurationat the C₃ position of L-(-)-carnitine (theCHOH group) is indeed R. This was accomplished usingthe gold atom asan anomalously-scattering source. Then stereospecificallydeuterated L-(-)-[2-D] carnitine was prepared bythehydration of trans-crotonobetaine in D₂O usingpurified L-carnitine dehydratase from Escherichiacoli. The subsequentneutron analysis of deuterated[(CH₃)₃N-CH₂-CH(OH)-CH₂-COOH]⁺[AuCl₄]^- revealed that the CHD group atpositionC₂ also had the absolute R configuration, thusestablishing that the addition ofD₂O across the C=Cdouble bond oftrans-crotonobetaine proceeds by a stereospecific syn pathway.In contrast, all other hydration-dehydrationreactionsexamined thus far show that, when the proton added or abstracted isbonded to a carbon atom that is adjacent to acarboxylate group, the absolute stereochemistry of the resultingtransformation is anti. Crystallographic detailsfor[(CH₃)₃N-CH₂-CH(OH)-CHD-COOH]⁺[AuCl₄]^-are as follows: space groupP2₁2₁2₁ (orthorhombic),a = 10.855(2), b = 11.678(3), c = 22.776(6)Å; Z = 8; final agreement factor for the neutron analysisat 15 K: R(F_o) =0.097based on 1140 reflections with I >3fchars/sigma.gif" BORDER=0 >(I).