Structure and configuration

Determination of the structure of an amide of a carbohydrate is not difficult. Examination of acyl derivatives indicates whether a cyclic or an acyclic structure is present. Moreover, the results of oxidations with periodate and lead tetraacetate allow unequivocal determination of these structures alternatively, methylation studies have been used. 

The first oxidative studies on N-acylglycosylamines were conducted on a preparative scale by Niemann and Hays.65 The N-acetyl-D-glucopyranosylamine (69) obtained by acetylation of D-glucopyranos-ylamine with ketene (or by acetylation of this amine, followed by ammonolysis) was oxidized by way of the dialdehyde 70 to the acid 71, isolated as the strontium salt. Hydrolysis of 71 led to D(+)-glyceric acid (72), thus showing the pyranose structure of 69. 

The oxidation of N-acylglycopyranosylamines on a semimicro scale is straightforward and overoxidation does not occur this was evident in the oxidation of an ZV-benzoyl-L-rhamnopyranosylamine10 and of the anomeric pair of IV-acetyl-D-galactopyranosylamines.66 These anomers were obtained by deacetylation of the pentaacetates of a- and /3-D-galactopyranosylamine. On periodate oxidation, the dialdehydes obtained (73 and 74) showed specific rotations of [a]D +60° and [a]D —96°, respectively. 

As the only difference between the two oxidation products is the configuration at the carbon atom that had been the anomeric center, it was possible to determine the configuration of C-l of other N-acetyl-hexopyranosylamines by comparison of the specific rotations of the dialdehydes formed by their oxidation with periodate. In this way, the anomeric configuration of N-acetyl-/3-D-glucopyranosylamine 

When applied to N-acylglycofuranosylamines, the periodate oxidation showed an abnormal uptake of oxidant ( overoxidation ). For example, when oxidized with lead tetraacetate12 and with periodate,1065 N-acetyl-a-D-glucofuranosylamine (15) afforded formaldehyde (indicating a furanose structure), and it consumed more than 5 moles of oxidant per mole. This result can be attributed to subsequent oxidation of the formic acid produced,69 or to the formation,10 by hydrolysis, of the intermediate 2-hydroxypropanedial (tartron-aldehyde) (77) that would then be oxidized. This tendency to undergo overoxidation has been found common for the furanoid N-acyl-gly cos y lam ines.24,25 

In the D-fructosides the convention is that the more dextro-rotatory anomer is the a form. Attempts have been made by Boeseken and Couvert,82 Verschuur83 and MacPherson and Percival84 to apply Boese-ken s boric acid method to determine the configuration of D-fructose at C2. The problem is much more complex than for aldoses because there are three hydroxyl groups near the reducing center, and also because the mutarotation of D-fructose involves the conversion of some pyranose to furanose form with the loss of a pair of cis hydroxyls (on C4-C5). This work has been discussed by Boeseken88 but no conclusion has been reached. 

Because of similarities in the properties and reactions of sorbose and fructose, Schlubach and Graefe86 suggested that a-L-sorbose is closely related to /3-D-fructose. This was further investigated by Ohle87 who showed experimentally that /3-D-fructose and a-L-sorbose have the same configuration except at C5. Hudson88 has suggested that in /3-D-fructose the hydroxyls on C2 and on C3 are cis. 

Beevers and Cochran89 have indicated by x-ray analysis, that in sucrose the hydroxyls on C2 and C3 of the fructofuranose part are cis thus sucrose is, according to Hudson s suggestion, a /3-D-fructofuranoside. 

The crystal structure of fructose has been studied by Eiland and 

Pepinsky59 by the x-ray analysis of the strontium chloride complex. The specific rotation of this compound indicates the /S-D-pyranose structure and the only model of this structure which is in accord with the Fourier projection is the Sachse-Mohr trans (chair) form, with cis hydroxyls on C2 and C3. 

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In general, resins are compatible with a large number of materials (oils, plasticizers, polyethylene waxes, rubbers). Compatibility depends on resin type, molecular weight and its distribution, resin structure and configuration, and finally on application requirements. 

Chemical development Proof of structure and configuration are required as part of the information on chemical development. The methods used at batch release should be validated to guarantee the identity and purity of the substance. It should be established whether a drug produced as a racemate is a true racemate or a conglomerate by investigating physical parameters such as melting point, solubility and crystal properties. The physicochemical properties of the drug substance should be characterized, e.g. crystallinity, polymorphism and rate of dissolution. 

Debenzylidenation of compound 24 yielded a crystalline glycoside 25 and the extent and rate of its periodate oxidation supports the structure and configuration shown. 

MeS(0)CHMe2, Et2S=0] support the S-bonded structures and configurations of the complexes shown in Scheme 15. Far-IR studies indicate that the Pd(II) complexes have uniformly the trans structure while the Pt(II) complexes have the cis one196 197. 

Lespieau, R., Synthesis of Hexitols and Pentitols from Unsaturated Poly-hydric Alcohols, II, 107-118 Levi, Irving, and Purves, Clifford B., The Structure and Configuration of Sucrose (oipta-D-Glucopyranosyl beta-D-Fructofuranoside), IV, 1-35 Liggett, R. W., and Deitz, Victor R., Color and Turbidity of Sugar Products, IX, 247-284... 

A repeating unit for S6 was proposed by Rebers and Heidelberger,29 as discussed in Ref. 1. The only features not determined were the structure and configuration of a ribitol phosphate moiety. From biosynthetic considerations,6 the phosphate group should be linked to 0-5 of D-ribitol, and the structure should, therefore, be that depicted in 10. 

Reactions of p-Functionalized a-Nitrosoalkenes with the C,C Double Bond The reactivity of a-nitrosoalkenes toward double bonds depends drastically on the structure and configuration of the reagents. The characteristic features of the behavior of p-functionalized a-nitrosoalkenes were studied using readily available methyl p-nitrosoacrylate (530a). It appeared that this derivative is readily involved in the ene reactions with electron-donating and neutral olefins either... 

Reductive desulfurization with Raney nickel of the mercaptolysis products of streptomycin has supplied one of the keys to the elucidation of the structure and configuration of that antibiotic. Since the chemistry of streptomycin has recently been reviewed37 the reactions discussed here will be considered solely as examples of hydrogenolysis and their bearing upon the problem of the structure and configuration of streptomycin will be ignored. 

The facility with which 1,5-anhydroglycitols of known structure and configuration may be synthesized through reductive desulfurization has resulted in the accumulation of sufficient new data on compounds of this class so that some generalizations have already been made concerning the relationship of configuration to rotatory power in this interesting series.t(... 

The indifference of /3-fructofuranosidase towards substitution in the afructon part of sucrose is contrasted by its extreme sensitivity towards any change in the structure and configuration of the fructon. Change from the furanose to the pyranose ring structure in methyl /3-D-fructoside is incompatible with the action of /3-fructofuranosidase.60... 

Irving Levi and Clifford B. Purves, The Structure and Configuration of... 

The glycol cleavage has also been useful in the determination of structure and configuration of a natural octulose and a natural nonulose. 

The proportions of the different kinds of initial groups depend on the nature and rate of the different transfer reactions by which they are formed and the proportion of initial groups derived from the catalyst will depend on the ratio of the rate of initiation to the sum of the rates of the transfer reactions. Finally, although the main chain of the polyisobutene molecule is very resistant to chemical attack [14], by virtue of its chemical structure and configuration, the end-groups are readily attacked by atmospheric oxidation. 

Murata, M., et ah. Structures and configurations of ciguatoxin from the moray eel Gymnothroax javanicus and its likely precursor from the dinollagellate Gambierdiscus toxicus, J. Am. Chem. Soc., 112, 4380, 1990. 

Twenty-four years elapsed after the conclusion of Vongerichten s researches on apiose before the study of its structure and configuration was undertaken by Schmidt. He prepared 500 grams of purified... 

The fundamental difficulty is that polymeric substances cannot be obtained in a structurally and molecularly uniform state, unlike low-molecular-weight compounds. Thus, macromolecular materials of the same analytical composition may differ not only in their structure and configuration (see Sect. 1.2) but also in molecular size and molecular weight distribution they are polydisperse, i.e., they consist of mixtures of molecules of different size. Hence, it is understandable that the expression identical is not, in practice, applicable to macromolecules. Up to the present time, there is no possibility of preparing macromolecules of absolutely uniform structure and size. It follows, therefore, that physical measurements on polymers can only yield average values. The afore-... 

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