Ronald J. Voll

Isolation of 2,5-anhydro-1,3-O-isopropylidene-6-O-trityl-D-glucitol and conformations of its 4-O-substituted and deprotected, acylated derivatives☆☆☆

Abstract Acidic dehydration of D -mannitol ( 1 ) gave a mixture of anhydrides ( 2 ) that was isopropylidenated and subsequently tritylated. A single component crystallized from the resulting mixture and was shown to be the novel 2,5-anhydro-1,3- O -isopropylidene-6- O -trityl- D -glucitol ( 4 ) by chemical and physical analysis and by comparison of its deprotected, dibenzoylated derivative ( 10 ) with authentic 2,5-anhydro-1,6-di- O -benzoyl- D -glucitol. Acid hydrolysis of 4 afforded pure 2,5-anhydro- D -glucitol ( 9 ) in better yield than by the previously reported route. The 4- O -acetyl ( 5 ), 4- O -chloro-acetyl ( 6 ), 4- O -methyl ( 7 ), and 4- O -(methylsulfonyl) ( 8 ) derivatives of 4 , the tetra- O -acetyl ( 11 ) derivative of 9 , and the 3,4-di- O -acetyl ( 12 ) derivative of 10 , have been prepared and spectrally characterized. Complete proton-n.m.r. analysis yields first-order coupling constants that indicate the E 1 ( D ) conformation for the tetrahydrofuran ring and the chair conformation for the 1,3-dioxane ring of 4-2-8 . Obtainable coupling constants suggest that 11 and 12 exist in the o E and/or o T 1 , conformations.

A proposed model for the regulation of phosphofructokinase and fructose 1,6-bisphosphatase based on their reciprocal anomeric specificities.

An often overlooked aspect of carbohydrate metabolism is that most carbohydrates in solution are mixtures of several constitutional and configurational isomers (acyclic forms and anomers), each present in different concentrations and capable of displaying a different affinity and reactivity for enzyme catalytic and allostenc sites (anomeric specificity). In this paper, the possibility is considered that this characteristic isomerism of carbohydrates might provide the basis for regulation of the enzymes that metabolize them, using the example of the phosphofructokinase/ fructose 1,6-bisphosphatase enzyme pair. Several investigators have pointed out the possibility that anomedc specificity may play a regulatory role [1-5] ; however, until now no mechanism has been proposed to show how this regulation may be achieved. The basis for the regulatory mechanism proposed in this communication is the recent harvest of data concerning the anomeric equilibria of carbohydrates in solution (reviewed in [6,7] ) and the anomeric specificity of the enzymes of glucose metabolism (reviewed in [2,4] ). D-Fructose 6-phosphate (F6P) and D-fructose 1,6-bisphosphate (FBP) have been shown by laC NMR spectroscopy to be equilibrated mixtures in aqueous solution (fig.l), composed of

Reassignment of the methine resonances of D-fructose based on the carbon-13 N.M.R. spectrum of 3-O-methyl-D-fructose.

Abstract Several disagreements in the 13 C n.m.r. assignments of the methine carbons of D-fructose exist in the literature. In order to settle these inconsistencies, we examined the 13 C n.m.r. spectrum of 3-O-methyl-D-fructose. By following the methyl induced shift in this spectrum, as compared to the parent sugar, we identified the alkylated C-3 resonance of all four tautomeric forms of D-fructose. This information, together with our previous identification of the C-5 resonances of the α- and β-forms of D-fructofuranose 6-phosphate, allow the unambiguous identification of all methine carbons of D-fructose in its 13 C n.m.r. spectrum. The tautomeric composition of 3-O-methyl-D-fructose at 16.5°, in aqueous solution, was found to be as follows: α-pyranose 18%, β-pyranose 37%, α-furanose 11% and β-furanose 34%.

Stereoselective carbohydate synthesis via palladium hydroxide catalyzed epoxide hydrogenolysis

Abstract 2,5:3,4-Dianhydro-D-altritol ( 1 ) reacts with lithium aluminum hydride to produce a 50:50 mixture of the epimeric alcohols ( 2 ) and ( 3 ) in fairly good yield. However, when 1 is catalytically hydrogenated in the presence of palladium hydroxide on charcoal (Pearlmans catalyst), the ratio of epimers formed changes to 99:1 ( 2:3 ) as determined by GC of the corresponding acetylated derivative compounds. The stereochemistry of the epimers has been determined by NMR spectroscopy.

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.

Two-dimensional 1H-, 13C-, and 31P-nuclear magnetic resonance and molecular-mechanics investigation of d-fructose 2,6-bisphosphate

Two-dimensional nuclear magnetic resonance studies have been carried out to assign unequivocally all the proton, carbon, and phosphorus resonances of D-fructofuranose 2,6-bisphosphate (1) and to verify its structure using a 400-MHz spectrometer. Several unexpected chemical-shift values and coupling constants were obtained. Molecular mechanics calculations (Sybyl) carried out to minimize the conformational energy of 1 yield phi C-1,P-2 = + 84, phi C-3,P-2 = - 155, and phi C-5,P-6 = + 175. Thus the unusual near-gauche orientations of C-1 and C-3 to P-2 in 1 can explain their small vicinal coupling constants (3JC-1,P-2 = 1.2, and 3JC-3,P-2 = 3.8 Hz), in contrast to the expected larger value seen for 3JC-5,P-6 namely, 6.9 Hz. Treatment of a sample of this compound with sodium borohydride did not affect its nuclear magnetic resonance spectrum, substantiating that O-2 is phosphorylated. Oxidation with sodium periodate yielded an intermediate which decomposed by a beta-elimination mechanism involving the 6-phosphate group. These data establish unequivocally the 1H, 13C, and 31P assignments and explain the observed anomalous shifts. Moreover they indicate that the activator of fructose 6-phosphate 1-kinase is the beta anomer of the 4T3 conformer of D-fructose 2,6-bisphosphate.

The x-ray crystal structure of 2,3:4,5-di-O-isopropylidene-1-O-methyl-β-d-fructopyranose

2,3:4,5-Di-O-isopropylidene-1-O-methyl-beta-D-fructopyranose, C13H22O6, Mr = 274.3, orthorhombic, P212121, a = 12.388 (2), b = 13.307 (5), c = 8.660 (1) A, V = 1427.4 (9) A3, Z = 4, Dm = 1.24 g.cm-3, Dx = 1.276 g.cm-3, CuKalpha, lambda = 1.54184 A, mu = 8.0 cm-1, F(000) = 592, T = 295 (1) K, R = 0.032 for 1586 observations (of 1693 unique data). The molecule is a derivative of the naturally occurring carbohydrate D-fructose. The data reported here indicate that the ketose six-membered ring is constrained by the presence of two fused five-membered rings into the 3SO conformation. These findings agree with the n.m.r.-spectroscopic results for 2,3:4,5-di-O-benzylidene-beta-D-fructopyranose. As a result of crystal packing forces, the exocyclic side-chain has a C-C-O-C torsion angle of -102 degrees, quite different from the expected value of 180 degrees.

Ab initio SCF energy calculations of the rotational orientation of each of the exocyclic groups of 6-O-methyl-β-d-tagatofuranose

Abstract Presented herein are potential-energy functions for the two side chains of a methyl ether of d -lyxo-2-hexulose, namely, 6-O-methyl-β- d -tagatofuranose, a model for β- d -tagatofuranose 6-phosphate. The methyl ether was chosen because, sterically, it is a good model of the phosphate, and yet it does not introduce the overwhelming complexity of phosphorus d orbitals into the calculations. The original minimum-energy structure for this molecule was obtained by using an empirical program, developed by Warshel, Lifson, and Karplus, which determined that the 4T3( d ) conformation is a minimum-energy structure; this was verified by our ab initio calculations. However, substantial differences were found in the minimum potential-energy structures of the two exocyclic groups. The equilibrium rotational orientation of each of these groups was then calculated. The results indicated that rotamers of angles 195° (for C-2) and 65° (for C-5) are very minor components. The calculations indicated that the molecule should mainly exist in two equal proportions as the two rotamers, one having angles of 295° (for C-2) and 290° (for C-5) and the other, angles of 75° (for C-2) and 290° (for C-5). All ab initio calculations were performed by using modified versions of the Gaussian-70 and Gaussian-76 programs at the STO-3G level.

Structure of 2,5:3,4-dianhydro-D-altritol

3,6-Dioxabicyclo[3.1.0]hexane-2,4-dimethanol, C6H10O4, M(r) = 146.1, orthorhombic, P2(1)2(1)2(1), a = 7.6209 (2), b = 9.1292 (3), c = 9.6135 (5) A, V = 668.8 (1) A3, Z = 4, Dx = 1.451 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 1.15 cm-1, F(000) = 312, T = 298 K, R = 0.029 for 1280 observations with I greater than 3 sigma(I) (of 1695 unique data). The tetrahydrofuran ring has the envelope conformation, OE, with P of 94.3 degrees and tau m = 24.0 degrees. C atoms deviate from their best plane by +/- 0.0006 (1) to 0.010 (1) A, and the O atom lies 0.331 (1) A from that plane. The epoxide O atom is syn to the tetrahydrofuran O atom. Each hydroxy group is involved in intermolecular hydrogen bonding both as donor and acceptor. The two hydrogen bonds have O...O distances of 2.743 (1) and 2.729 (1) A, and angles about H of 166.3 (12) and 172 (2) degrees, respectively.

Structure of 1,2,3,4,5,6-hexa-O-acetyl-myo-inositol

C18H24O12, Mr = 432.4, monoclinic, Cc, a = 8.996 (3), b = 20.890 (6), c = 11.872 (4) A, beta = 101.11 (2) degrees, V = 2189 (1) A3, Z = 4, Dx = 1.312 g cm-3, Mo K alpha, lambda = 0.71069 A, mu = 1.05 cm-1, F(000) = 912, T = 163 K, R = 0.041, wR = 0.0375 for 2158 reflections (Fo greater than or equal to 6 sigma magnitude of Fo). The ring is in the chair conformation 4C1 with five equatorial groups and one axial group bonded to C(2) as expected. The carbonyl bonds of the acetate groups at positions 2, 4, 5 and 6 are approximately coplanar with their respective ring C-H bonds. However, those at positions 1 and 3 are rotated towards the H(2) atom.