Norman S. Bhacca

Physical studies on oligosaccharides related to sucrose. : Part I. N.M.R. studies on the peracetates of sucrose, 1-kestose, and nystose☆

The n.m.r. spectra of sucrose octaacetate (1), 1-kestose hendecaacetane (2), and nystose tetradecaacetate (3) were measured in benzene-d6, chloroform-d, and acetone-d6, at 100 and 220 MHz. Signals of H-1, 2, 3, and 4 of the α-d-glucopyranosyl residue, and of H-3 and H-4 of the β-d-fructofuranosyl residue(s), could be observed individually for each of the compounds. The data confirm that all d-fructose residues in 1-kestose and nystose are in the furanoid ring-form. Observation of a two-proton, AB system near τ 6.3 (chloroform-d) in the spectrumof 2 provides diagnostic evidence for the (2↔1) linkage between the two d-fructofuranosyl residues in 1-kestose [β-d-Fruf-(2→1)-β-d-Fruf-(2↔1)-α-d-Gp]; other conceivable linkages are excluded. A second such AB system, observed in the spectrum of 3, establishes that nystose is built up from 1-kestose by (2→1) attachment of an additional d-fructofuranosyl group. Other points of attachment are excluded, and the structure β-d-Fruf-(2→1)-β-d-Fruf-(2→1)-β-d-Fruf-(2↔1)-α-d-Gp previously suggested for nystose, is confirmed. The n.m.r. signals for H-2, 3, and 4 of the α-d-glucopyranosyl residue in 1, 2, and 3, and also in methyl α-d-glucopyranoside tetraacetate (4), showed close correlation.

Conformational studies on pyranoid sugar derivatives. : The conformational equilibria of δ-d-ribopyranose tetraacetate and β-d-xylopyranose tetraacetate

Abstract β- d -Ribopyranose tetraacetate ( 1 ) has been shown to exist, in acetone- d 6 at room temperature, as a 9:11 mixture of the 1C ( d ) and C1 ( d ) conformers in rapid equilibrium. The rate of chair-chair interconversion at −60° is 130 times per second. At −84°, a temperature at which n.m.r. spectral signals of the two separate conformers can be observed, the ratio of the 1C ( d ) to C1 ( d ) conformers is 2:1. For β- d -xylopyranose tetraacetate ( 2 ), in acetone- d 6 at room temperature, the all-axial, 1C ( d ) conformer exists in equilibrium with the all-equatorial, C1 ( d ) conformer to the extent of 1 part in 5. At −84°, the 1C ( d ) conformer was not detected.

Tautomeric composition of D-fructose phosphates in solution by fourier transform carbon-13 nuclear magnetic resonance

The Fourier transform 13C magnetic resonance spectra of D-fructose 6-phosphate (F6P) and D-fructose 1,6-diphosphate (FDP) were obtained. The signal assignments made on the basis of 13C chemical shifts and 13C-31P spin-spin couplings indicate that the earlier assignments of the C-4 and C-5 resonances of α- and β-fructofuranose in oligosaccharides and D-fructose [Allerhand, A. and Doddrell, D., J. Amer. Chem. Soc., 93, 2777, 2779 (1971)] should be reversed. Integration of signal intensities yields the following equilibrium composition at 35°C: F6P, α-anomer 19±2% and β-anomer 81±2%, FDP, α-anomer 23±4% and β-anomer 77±4%. Less than 1.5% keto or hydrated keto form is present in solutions of either fructose phosphate. The bearing of these findings on the tautomeric specificity of phosphofructokinase is discussed.

Viguilenin, a germacranolide from Viguiera linearis

Abstract The new germacranolide, viguilenin, was isolated from Viguiera linearis and its structure was established by chemical and spectroscopic means.

Investigations of dehydroepiandrosterone. Part I: crystal structure of sublimed DHEA

The crystal structure of an orthorhombic polymorph of the title compound, crystallized by sublimation, has been determined. Dehydroepiandrosterone, C19H28O2, space groupP212121 witha=6.6408(4)b=11.4423(11)c=22.085(2)Å,V=1678.2(4)Å3,Z=4. The structure was refined toR=0.051 for 2645 observed reflections. The conformation of the molecule is similar to that found in other polymorphs and solvates, with a chair A ring, an 8β, 9α half-chair B ring, a chair C ring, and a 14α envelope D ring. Molecules are linked in chains by OH...O hydrogen bonds involving the carbonyl oxygen atom. The O...O distance is 2.855(3) Å, and the angle about H is 171(2)o.

Purification of 2,5-anhydro-d-hexitol bis(phosphates) and identification of a major 1,4,6-tris(phosphate) contaminant by 31P-, 13C-, and 1H-N.M.R. spectroscopy☆☆☆

Abstract The reaction of two equivalents of diphenylchlorophosphate in cold pyridine with 2,5-anhydrohexitols has been assumed to result in only 1,6-bis(diphenylphosphate) products. However, by thin-layer, silica gel dry-column, and DEAE-Sephadex A-25 column chromatography, the products of this reaction have been shown to contain three major components; monophosphates (32 or 30%, by weight), 1,6-bis(phosphates) (40 or 56%), and 1,4,6-tris(phosphates) (28 or 14%): the former percentages for the product from 2,5-anhydro- d -mannitol (1) and the latter for the product from 2,5-anhydro- d -glucitol (10). The identity of each bis- and tris-(phosphate) of 1 or 10 was established by 31P- and 13C-n.m.r. spectroscopy. Acetylated bis- and tris-(diphenylphosphates) of 1 were also examined by 1H-n.m.r. The significance of these findings on the interpretation of studies of the anomeric specificity of enzymes and on the specificity of the reagent diphenylchlorophosphate are discussed. The formation of only a 1,4,6-tris(phosphate) of 10 suggests that the 1,6-bis(diphenylphosphate) of 10 may undergo formation of a 1,3-cyclic phosphate triester by transesterification with elimination of phenol. A method for the determination of the number of cyclohexylammonium groups crystallizing with a sugar phosphate is proposed that simplifies the elemental analysis of this type of salt.

Isosucrose. Definitive structural assignment by spectral correlation to α,β- and α,α-sucrose octaacetates

Abstract Three nonreducing disaccharides containing D -glucosyl and D -fructosyl groups, namely, “isosucrose” octaacetate ( 3 ), sucrose octaacetate ( 4 ), and “α,α-sucrose” octaacetate ( 5 ), give qualitatively identical mass spectra and are, therefore, related as diastereoisomers. Spin-coupling values in the 300-MHz n.m.r. spectra of 3 , 4 , and 5 establish that the D -glucopyranosyl group is present in the 4 C 1 ( D ) conformation, and that the anomeric configuration of this group is α in 4 and 5 , and β in 3 . In the n.m.r. spectra, the H-4 atom of the D -fructofuranosyl group of 3 and 5 resonates 0.5 p.p.m. upfield of the corresponding signal of 4 , from which it was deduced that both 3 and 5 are α- D -fructofuranosides.

Spectroscopic investigations of dehydroepiandrosterone. Part II: Photoelectron spectrum and electronic structure.

The gas phase electronic structure of dehydroepiandrosterone (3 beta-hydroxy-5 alpha-androstene-17-one, DHEA) is elucidated from its Het photoelectron spectrum, quantum chemical calculations, and correlation with spectra of the related molecules 5 alpha-androstene-17-one (I) and epiandrosterone (3 beta-hydroxy-5 alpha-androstane-17-one) (2). The lowest ionization energy event in DHEA is shown to correspond to a pi-ionization energy of approximately 8.5 eV, followed closely and overlapped in part by the carbonyl lone pair ionization at 8.7 eV.

Structural studies on a novel reaction product of malononitrile with aβb,δ-unsaturated allene aldehyde

Abstract Condensation of 2,5,5-trimethylhexa-2,3-dien-6-a1 with malononitrile affords an unexpected product, C15H16N4X, ( 3 ), the structure of which was partially characterized by spectral (infrared, ultraviolet, 1H, and 13C nmr) methods and fully elucidated by single crystal X-ray analysis. 3 is l-cyano-2-amino-3-(2-propenyl)-5,5-dimethy-6- dicyanomethycycohexa-l,3-diene in a half-chair conformation. Conjugation of the cis -aminocyanoethenyl moiety leads to intermolecular hydrogen bonding in the crystal. A reaction sequence and its mechanistic implications are proposed.

Carbon-13 and proton magnetic resonance study of the structure and conformation of a new germacranolide sesquiterpene dilactone

The structure of melampodin B, a new sesquiterpene dilactone isolated from Melampodium leucanthum, has been elucidated on the basis of physical properties, predominantly 13C and 1H n.m.r. data.