Joseph D. Wander

Conformation of acyclic derivatives of sugars. : Conformations of peracetylated aldose dithioacetals in solution

Abstract The peracetylated diethyl dithioacetals of d -ribose, d -arabinose, d -xylose, d -lyxose, l -rhamnose, and l -fucose were studied in chloroform- d solution by n.m.r. spectroscopy at 100 MHz. Signals of all protons were assigned, assignments were verified by spin-decoupling, and first-order coupling-constants were determined. For the d -arabinose, d -lyxose, l -rhamnose, and l -fucose derivatives, the coupling constants observed accord with a favored conformation in which the chain of carbon atoms is fully extended in a planar, zig-zag arrangement. The d -ribose and d -xylose derivatives, which, in a conformation having the carbon atoms in a planar, zig-zag arrangeent, would have a pair of parallel, eclipsed acetoxyl groups at C-2 and C-4, give coupling data completely inconsistent with such an extended, planar formulation. The data indicate that the favored conformation of the d -ribose and d -xylose derivatives is a “sickle” arrangement derived from the planar, zig-zag conformation by rotation (about the C-3C-4 bond in the d -rihose derivative, and about the C-2C-4 bond in the d -xylose derivative) to rotamers in which the steric interaction between substituents at C-2 and C-4 is relieved.

Analysis of sugar derivatives by chemical-ionization mass-spectrometry

Abstract D -Glucose diethyl dithioacetal ( 1 ), its penta- O -acetyl derivative ( 2 ), penta- O -acetyl- aldehydo - D -glucose ( 3 ), L - xylo -hexulose phenylosotriazole ( 4 ), 1,2:5,6-di- O -isopropylidene- D -mannitol ( 5 ), 1,2:4,5-di- O -isopropylidene-β- D -fructopyranose ( 6 ), 1,2- O -isopropylidene-α- D -glucofuranose ( 7 ) and its triacetate ( 8 ), 1,6-anhydro-β- D -galactopyranose ( 9 ) and its triacetate ( 10 ), D -glucopyranose ( 11 ), methyl β- D -glucopyranoside tetraacetate ( 12 ), 1-thio-β- D -glucopyranose pentaacetate ( 13 ), β- D -fructofuranose pentaacetate ( 14 ), and raffinose hendecaacetate ( 15 ) have been examined by chemical-ionization mass-spectrometry with both isobutane and ammonia as ionizing intermediates. Extreme simplicity characterizes these spectra, and, in most instances, molecular-weight data are available from intact, protonor NH 4 + capture ions; the limited fragmentation that occurs corresponds in large measure to simple dehydration or substituent-cleavage processes, and is strongly dependent upon the groups present, so that considerable information about the substituent groups in the sugar molecule may be inferred.

Dithioacetals of Sugars

Publisher Summary This chapter provides an overview of dithioacetals and their direct chemical transformations. Dithioacetals and their derivatives comprise the largest recorded class of acyclic carbohydrate derivatives. They are versatile intermediates in synthesis not only because a multitude of transformations are possible at the dithioacetal group, but also because all of the hydroxyl groups of the sugar chain are available for chemical transformation or selective protection. Of particular importance is the fact that they provide a route for kinetically controlled ring-closure of the sugar under neutral conditions by the action of mercury (II) salts, thus providing a useful route of access to furanosides. Although dithioacetals are odorless, an inherent practical disadvantage of their preparation is the generally disagreeable scent of the lower thiols. Furthermore, appended to this chapter is a set of tables that lists the melting points and specific rotations of sugar dithioacetals and certain derivatives.

Diphenyl dithioacetals of d-ribose, d-xylose, and d- and l-arabinose. Conformational studies and formation of a ketene diphenyl dithioacetal

Abstract d -Ribose, d -xylose, d -arabinose, and l -arabinose have been converted in good yield into their respective diphenyl dithoacetals, 1, 5, 8, and 3. The tetraacetate 4 of 3 adopts a planar, zigzag conformation in chloroform solution, but the d -xylo analog 6 and d -ribo analog 2 adopt conformations that have no parallel 1,3-interactions of acetoxyl groups. A crystalline diisopropylidene acetal 7 was obtained from 1. On treatment with a strong base, the corresponding acetal 9 from the d -arabino derivative 8 underwent elimination of acetone to give the ketene diphenyl dithioacetal 10, characterized as its crytalline 3-p-nitrobenzoate 11 and its remarkably stable 3-methyl ether 12.

Conformation of acyclic derivatives of sugars : Part VI. Conformations of aldehydo-aldose peracetates in solution☆☆☆

Abstract 2,3,4,5-Tetra- O -acetyl- aldehydo - d -ribose ( 1 ), its d - arabino ( 2 ), d - xylo ( 3 ), and d - lyxo ( 4 ) analogs, and 2,3,4,5-tetra- O -acetyl-6-deoxy- aldehydo - l -galactose ( 5 ) have been studied in chloroform- d solution by n.m.r. spectroscopy at 100 MHz. Signals of all protons were assigned, and verified by spin decoupling, and first-order coupling-constants were determined. The favored conformation of these compounds was shown to be the extended, planar, zigzag form 2 , except when such a conformation would lead to an eclipsed, 1,3-interaction between pairs of substituents, in which case the favored conformation is a “sickle” form 3–5 in which the 1,3-interaction is alleviated, by rotation about a carbon-carbon bond of the chain, to give a different rotameric state. The diphenyl dithioacetals ( 8 and 9 , respectively) of 2,3,4,5-tetra- O -acetyl- d -lyxose and 2,3,4,5-tetra- O -acetyl-6-deoxy- l -mannose were prepared, and their conformations studied; demercaptalation of these compounds by mercuric chloride proved to be more difficult than with the diethyl analogs.

Physical studies on oligosaccharides related to sucrose: Part II. Mass-spectral identification of D-fructofuranosyl residues

Abstract Sucrose ( 1 ), melibiose ( 2 ), 1-kestose ( 3 ), planteose ( 4 ), raffinose ( 5 ), nystose ( 6 ), and stachyose ( 7 ) have been converted into their respective peracetates ( 1a , 2a , 3a , 4a , 5a , 6a , and 7a and per(trimethylsilyl) ethers ( 1b , 2b , 3b , 4b , 5b , 6b , and 7b ), and the two series of derivatives have been subjected to electron-impact ionization in a high-resolution mass spectrometer. The ethers show detectable molecular-ion peaks(up to m/e 1674 for 7b ) together with M + . -·CH 3 peaks, and the acetates show M + . -·OAc peaks. From the fragmentations observed, and the relative intensities of the fragments, it is possible to recognize in the oligosaccharides ( a ) the presence or absence of ketohexofuranosyl residues, ( b ) the terminal or nonterminal location of ketohexofuranosyl residues, and ( c ) the presence of ketohexofuranosyl residues (and their number) attached to adjacent residues through “methylene bridges”. A substantial temperature-dependence was observed in the intensities of certain ions.

Specific isotopic labeling of sugars. Specific c-deuteration of 1,6-anhydro-2,3-O-isopropylidene-β-D-talopyranose through enolization of an aldosulose derivative: n.m.r. spectral studies☆☆☆

Abstract Treatment of 1,6-anhydro-2,3- O -isopropylidene-β- D - lyxo -hexopyranos-4-ulose ( 1 ) with sodium deuteroxide in deuterium oxide leads to regiospecific and stereo-specific incorporation of deuterium at C-3, to give the 3- C -deuterated analog ( 2 ) of the ketone 1 . Reduction of 1 with sodium borohydride gives 1,6-anhydro-2,3- O -isopropylidene-β- D -talopyranose ( 3 ) stereospecifically, and the 4- C -deuterated analog ( 4 ) was obtained when the reduction was effected with sodium borodeuteride. Similar reductions of the deuterated ketone 2 gave the 3- C -deuterated analog ( 5 ) of 3 and the 3,4-di- C -deuterated analog ( 6 ) of 3 , respectively. The 100-MHz n.m.r. spectrum of 3 was interpreted completely by comparison of its spectrum with those of the deuterated analogs 4-6 . Alterations in the appearance (but not the field position) of various signals in the n.m.r. spectrum of 3 as a function of isotopic substitution permitted complete, reliable determination of chemical shifts and coupling constants for all protons in the molecule.

Determination of the configurations of tertiary alcoholic centers in branched-chain carbohydrate derivatives : PMR spectroscopy with a lanthanide shift-reagent

Abstract Examination of the PMR spectral changes (expressed as shift gradients of individual protons) wrought by graduated addition of the paramagnetic lanthanide complex tris [1,1,1,2,2,3,3-heptafluoro- 7,7-dimethyloctane-4,6-dionato]europium(III) [Eu(fod) 3 ] permitted assignment of the configuration at tertiary alcoholic centers of certain sugar derivatives. The configurations of the tertiary position of 3- C -(1,3-dithian-2-yl)-1,2:5,6-di- O -isopropylidene-α- d -allofuranose ( 1 ), lethyl of 4,6- O -benzylidene-2- deoxy-3- C -(dithian-2-yl)-α- d - ribo -hexopyranoside ( 2 ) and the corresponding 3- C -butyl compound ( 2a ), and methyl 2- C -(1,3-dithian-2- yl )-3,4- O -isopropylidene-δ- d -ribopyranoside ( 3 ) were assigned by comparison with reference spectra. The proton shift-gradients for 5- C -benzoyloxymethyl-2,3- O - cyclohexylidene-1- O - p -tolylsulfonyl-1( R ),2( S ),3( S ),5( R )-cyclohexanetetrol ( 4 ), taken in conjunction with the spin-spin coupling values, permit direct assignment of relative stereochemistry in the latter compound.

Calculation of molecular rotation by summation of partial conformational contributions : Part II. Rotations of the 1,6-anhydro-deoxy-β-d-hexopyranoses, 2,7-anhydro-β-d-heptulopyranoses, and their acetates

Abstract The optical rotations of two families of compounds, both having the 1,6-anhydro-β- d -hexopyranose structure as the fundamental skeletal unit, have been expressed as algebraic summations of empirical rotatory contributions from various conformational elements of asymmetry. The calculations have been made for 1,6-anhydro-monodeoxy-β- d -hexopyranoses and their diacetates, and for the 2,7-anhydro-β- d -heptulopyranoses and their tetraacetates, by using terms calculated 1 for the parent 1,6-anhydro-β- d -hexopyranoses and four new terms to describe interactions previously untreated. The calculated rotations are in satisfactory agreement with constants reported in the literature, and indicate conformational uniformity throughout the entire class of examples.

Chemical-ionization mass spectrometry of carbohydrates: Behavior of the antibiotic celesticetin under various conditions of ionization

Abstract The chemical-ionization mass spectrum of the polyfunctional carbohydrate antibiotic, celesticetin, is remarkably simple, in contrast to its electron-impact mass spectrum. With ammonia as the ionizing gas the protonated molecular ion is the principal species, and simple fragmentation modes reflect eleavage between principal moietics of the molecule. Substantial modifications of the fragmentation pathway are observed when isobutane is used as the ionizing gas. The different pathways of fragmentation according to the mode of ionization are interpreted in terms of differential reactivity of various heteroatomic centers in the molecule toward each of the ionizing agents. Use of a combination of ionizing modes may provide a useful general method for identification on a micro scale of complex carbohydrates isolated from fermentation or other mixtures.