Absolute Configuration of Chiral Ethanol-1-d:  Neutron Diffraction Analysis of the (−)-(1S)-Camphanate Ester of (+)-(R)-Ethanol-1-d

Abstract

The absolute configuration of (+)-ethanol-1-d has been determined to be R by the single-crystal neutron diffraction analysis of its (−)-camphanate ester. The absolute configuration of the (−)-camphanate group, which served as the chiral reference for the neutron study, was in turn established to be 1S,4R in an X-ray anomalous dispersion study of the complex Cu2(camphanate)4(ethanol)2. These results provide unambiguous confirmation that the optical rotation of (R)-ethanol-1-d (positive) is opposite to that of its higher homologs, (R)-propanol-1-d, (R)-butanol-1-d, and (R)-neopentanol-1-d (all negative), and demonstrates the usefulness of neutron diffraction in determining the absolute configuration of molecules possessing chiral methylene groups (i.e., molecules of the type CHDRR‘). Crystallographic details: for the neutron analysis of (+)-(R)-ethyl-1-d (−)-(1S)-camphanate: space group P21212 (orthorhombic), a = 6.422(1) Å, b = 21.004(4) Å, c = 9.275(2) Å, V = 1251.1(7) Å3, Z = 4; R(F 2) = 0.083, and wR(F 2) = 0.075 for 1114 reflections. For the X-ray analysis of Cu2(camphanate)4(ethanol)2: space group P1 (triclinic), a = 11.086(3), b = 11.244(3), c = 13.293(4) Å, α = 111.59(2), β = 107.71(2), and γ = 105.56(3)°, V = 1397.6(7) Å3, Z = 1; R(F) = 0.054, wR(F) = 0.058 for 3672 reflections.

Neutron Diffraction Structure of (2R,3R)-l-(−)-[2-D]Carnitine Tetrachloroaurate, [(CH3)3N-CH2-CHOH-CHD-COOH]+[AuCl4]-: Determination of the Absolute Stereochemistry of the Crotonobetaine-to-Carnitine Transformation Catalyzed by l-Carnitine Dehydratase from Escherichia coli

“…Although comparative NMR and optical rotatory data have been used extensively in the assignment of absolute configurations of deuterated products of enzymatic reactions, the unavailability of related molecules of known stereochemistry precluded the application of a similar approach to the stereospecifically synthesized monodeuterated l -carnitine. As outlined in the introduction, in more recent years application of single-crystal neutron diffraction techniques has allowed the unambiguous determination of the absolute configuration of several enzymatically synthesized molecules that possess chiral methylene groups. − In the present study the product of the l -carnitine dehydratase-catalyzed hydration of crotonobetaine in D 2 O was crystallized as the [AuCl 4 ] - salt and subjected to single-crystal neutron diffraction analysis. The results establish the product of the enzymatic synthesis to be (3 R ,2 R )-carnitine-2- 2 H, a finding that is consistent with an l -carnitine dehydratase- catalyzed stereospecific syn addition to the trans CC double bond of crotonobetaine (Scheme ).…”

“…In the past few years, we have used neutron diffraction to determine the absolute configurations of several molecules that have chiral methylene groups (i.e., molecules of the type CHDRR*). Examples of molecules that we have studied include stereospecifically-deuterated malic acid (HOOC−CHD−CHOH−COOH), succinic acid (HOOC−CHD−CH 2 −COOH), and derivatives of neopentanol [(CH 3 ) 3 −CHD−OH] and ethanol [CH 3 −CHD−OH] …”

Monoterpenoids (mid-1997 to mid-1999)

“…505 The absolute configuration of (ϩ)-[1-2 H]ethanol has been determined to be (R) by single-crystal neutron diffraction analysis of its ester with (Ϫ)-camphanic acid 354. 506 The He-1 photoelectron spectra of camphor 352 and of bromocamphor have been determined, 507 and EPR spectroscopy has been used to discriminate between the (R)-and (S)forms of the anion radical derived from camphorquinone 355. 508 The experiment was carried out in one of the chiral solvents (S,S)-or (R,R)-2,3-dimethoxy-1,4-bis(dimethylamino)butane saturated with sodium iodide in which ion association between the semidione and sodium ions occurs.…”

Diastereomeric metallatetrahedron complexes of the type Re2(AgPR3)2(μ-PCy2)(CO)7Z (R = Et and Ph; Z = (−)- and (+)-camphanate): synthesis, structure and CD data

“…This is the first crystallographically determined example of any bidentate carboxylate ligand for a heteronuclear Re-M moiety where M is a transition metal. For camphanate as bidentate ligand only two homonuclear structures are known: a dicopper complex 25 and a dirhodium complex. 26 In these the respective metal-oxygen bonds are of nearly equal length and differ only by about 0.03 Å.…”