Acyclic carbohydrate derivatives

Acyclic Carbohydrate Derivatives iV -Dimethyl-and iV -Dihexyh laramide Model Compounds for Synthetic Pofy(hexamethylene i laramide)... 

Finally, the mass spectra of acyclic carbohydrate derivatives will be considered in many aspects, these differ essentially from those of the cyclic forms. 

Acyclic carbohydrate derivatives containing unsaturation, with some exceptions, exhibit much of the chemistry already described for cyclic analogues, and their usefulness should not be overlooked. Unsaturated derivatives of alditols can be made, for example, by standard eliminations from alditol v/r-disulfonates or epoxides or by /f-eliminations from O-substituted 1-deoxy-l-nitroalditols and 1-deoxy-l-sulfonylalditols. Additions of hydrogen and ammonia to the unsaturated nitroalditols made in this way offer, respectively, routes to 2-deoxy- and 2-amino-2-deoxyaldoses.255... 

The Wittig extension of the d- or L-arabinose chain leads to acyclic carbohydrate derivatives 8 and 11. The thermal cycloaddition of 8 and cyclopentadiene is reported to produce the single adduct 96, but this result has proved to be erratic7 [it was discovered that 8 had been prepared from D- (not L-)arabinose and the optical rotation of 10 was compared with a published value for 10, which has only 25% ec optical purity). 

Acyclic carbohydrate-derived dienes have been described by Reitz, Jordan, and Maryanoff. Diene 54, derived from arabinose, underwent cycloaddition to N-phenylmaleimide to give lactone 56 in a yield of 51% 28). A minor isomeric product was also obtained in 16% yield. The major product results from an intramolecular acylation of the initial endo cycloadduct. The stereoselectivity of the addition was found to be consistent with that reported in other studies involving koxy-substituted dienes. 

The successful selective modification of the cycloamyloses must overcome rather severe synthetic difficulties derived primarily from the multiplicity of potentially reactive cycloamylose hydroxyl groups. Utilizing techniques developed for the modification of acyclic carbohydrates, the cycloamyloses... 

The preparation of C-1 glycals has been largely addressed by synthetic modifications on cyclic carbohydrate derivatives, although strategies that rely on ring forming reactions from acyclic derivatives have recently emerged (Fig. 1). 

Acyclic carbohydrates with one alkyl chain are either derived from cyclitols or aldonic acids. Acyclic cyclitol derivatives 3 (X=0, S, NH, N(CH3), NHCO, N(CH3)C0 R=Q-Ci6 sug=Glc-ol, Man-ol) form thermotropic liquid crystals... 

The stereoselective normal electron demand Diels-Alder reaction of chiral 13-diaza-13-butadienes 42, derived from acyclic carbohydrates, with diethyl azodicarboxylate 2 yields the corresponding functionalized l,23,6-tetrahydro-133,4-tetrazines 43. The observed stereoselectivity is markedly dependent on the relative stereochemistry at C-1 3 - Reactions proceed slowly in benzene solution at room temperature, but are greatly accelerated by microwave irradiation <99JOC6297>. 

The acyclic dithioacetal derivatives formed from reactions with such thiols offer a variety of reaction modes for the synthesis of modified sugars, as well as for the total synthesis of enantiomericaEy pure natural products and, as such, are attractive and versatile intermediates in synthetic carbohydrate chemistry. 

M. L. Wolfrom and A. Thompson, Acyclic monosaccharide derivatives, Methods Carbohydr. Chem. 2 427 (1963). 

J. Marco-Contelles, C. Pozuelo, M. L. Jimeno, L. Martinez, and A. M. Grau, 6-exo Free radical cyclization of acyclic carbohydrate intermediates A new synthetic route to enantiomerically pure polyhydroxylated cyclohexane derivatives, J. Org. Chem. 57 2625 (1992). 

Marco-Contelles, J. et al. (5-Exo Free Radical Cyclizalion of Acyclic Carbohydrate Intermediates A New Synthetic Route to Enantiomerically Pure Polyhydroxylated Cyclohexane Derivatives. 3.1 1992 [144]... 

Considerable work was done to induce chirality via chiral auxiliaries. Reac tions with aromatic a-ketoesters like phenylglyoxylates 21 and electron-rich al kenes like dioxoles 22 and furan 23 were particularly efficient (Scheme 6). Yield up to 99% and diastereoselectivities higher than 96% have been observed whet 8-phenylmenthol 21a or 2-r-butylcyclohexanol 21b were used as chiral auxiliarie [14-18]. It should be noted that only the exoisomers 24 and 25 were obtained from the reaction of dioxoles 22. Furthermore, the reaction with furan 23 wa regioselective. 24 were suitable intermediates in the synthesis of rare carbohydrate derivatives like branched chain sugars [16], Other heterocyclic compounds liki oxazole 28 [19] and imidazole 29 [20] derivatives as well as acyclic alkenes 3fl 31, and 32 [14,15,21,22] were used as olefinic partners. Numerous cyclohexane derived alcohols [18,21-24] and carbohydrate derivatives [25] were used as chiri... 

At pH 10, diphenylborinic acid gives a tetrahedral anion that complexes with various diol systems, and thus it can be used in electrophoresis like borate.109 In a more detailed study of such complexing,110 diols were examined by 13C-n.m.r. spectroscopy, before and after addition of sodium diphenylborinate, and complexes were detected, and their spectra observed, for a variety of carbohydrate derivatives. 1,2-Diol groupings in acyclic and cis-cyclic compounds, 1,3-related diols at C-4,C-6 of hexopyranosides, the 3,5-diols of glucofuranoses, and 2,4-diols of the anomeric methyl 3,6-anhydro-D-glucopyranosides were all found to react. No interaction occurred with l,6-anhydro-/3-D-glucopyranose (compare Section V,2). 

The Synthesis of Carbohydrate Derivatives from Acyclic Precursors. Ager, D. I East, M. B. Tetrahedron 1993, 49, 5683-5765. 

The addition of allyltrimethylstannane to a-oxygenated aldehydes can be effected with 5 M LiClOa in ether [19]. These additions afford mainly the syn adducts with a variety of acyclic and carbohydrate-derived aldehydes (Eq. 12). 

The interpretation of the mass spectra of oligosaccharide derivatives follows the general principles that have been elaborated for simple cyclic and acyclic carbohydrates (66MI1 74MI1). 

Horton et al. were interested in the synthesis of tetra-C-substituted carbocycles, and extensively studied asymmetric Diels-Alder reactions employing acyclic unsaturated carbohydrate derivatives. Thus, the thermal cycloaddition of the D-arabinose-derived c/i-dienophile (Z)-100 with cyclopentadiene gave endo-adduct 101 in excellent optical purity. The high diastereo-facial differentiation in this reaction arises from a highly favored conformation at the allylic center [76,77] (Scheme 10.33). Therefore, conformer 102 seems to be more favored than 103, where the latter suffers from severe allylic strain between the methoxycarbonyl and the C4-acetoxy group... 

A non-specific bacterial acid phosphatase from Shigella flexneri (PhoN-Sf) has been screened for regioselective phosphorylation of primary alcohol(s) of more than 20 different cyclic and acyclic monosaccharides using pyrophosphate as the phosphate donor (O Scheme 61) [368]. These studies have shown that PhoN-Sf is capable of phosphorylating a range of hexoses (D-glucose epimers, glycosides, and C-2 derivatives), pentoses, heptoses, ketoses, and acyclic carbohydrates. 

Cyclic sulfates can be prepared from cyclic but not acyclic carbohydrate units by reaction with sulfuryl chloride in pyridine [98] or phenyl chlorosulfate and sodium hydride [99]. The reactivity of cyclic sulfates is quite similar to that of epoxides. Thus, they can be used to form fluoro or azido derivatives of polysaccharides by highly regiospecific approaches, usually, but not always, leading to trans-diaxial products from which the sulfate can be easily removed by mild, acid-catalyzed hydrolysis [100,101]. 

---