Aldononitriles

Elimination of multiple peaks may also be achieved by conversion of a sugar into the dithioacetal or the nitrile. The suitability of the former type of derivative for g.l.c. appears to have been explored only in a model study on xylose methyl ethers. Lance and J. K. N. Jones also demonstrated that the acetylated nitriles derived from diese ethers give sharp, single peaks, and permit 2- and 3-0-methyl-i -xylose to be distinguished from each other, a resolution not achieved by using alditol acetates. Nitriles have been used by Bouhours and Cheshire to demonstrate the occurrence of the same two xylose ethers in peat, and by Bacon and Cheshire to prove the natural existence of 3-O-methyl-D-galactose in leaves. 

Reduction of some methylated sugars produces a symmetrical alditol this can introduce ambiguities when the pattern of substitution is to be determined by mass spectrometry (see Section XXV p. 37). Such problems are obviously avoided by (he use of didiioacetals or nitriles. For this reason, Dmitriev and coworkers investigated both the g.l.c. and mass spectrometry of acetylated nitriles. 

Investigations that have involved separations of trimethylsilyl ethers of alditols are listed in Table XXV (see p. 88) Tables XXVI (see p. 89), XXVII (see p. 99), and XXVIII (see p. 100) record separations based on alditol acetates, trifluoroacetates, and aldononitrile acetates, respectively. The retention times of alditol acetates have been tabulated.  

This degradative technique has been applied in the study of gums, which commonly give rise to complex mixtures of methylated sug-ars 106,837,8 9,870 fijg method may also be used as part of a rigorous proof of the structm-e of a particular compound isolated, as in the conversion of a tri-O-methyl-D-mannose into a tri-O-methyl-L-arabinose, or of a synthetic product.  

Similar transformations are useful in determining the nature of hep-toses (either before or after methylation), for demonstrating the existence of hexofuranose units in a polysaccharide, and for studying the products obtained from amino sugars by reaction with ninhydrin.  

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Propionylated aldononitriles, prepared by Gim nez, have been degraded in a similar way and the dipropionamide derivatives of the lower sugars obtained without difficulty. 

The fact that each monosaccharide may give more than one peak owing to the formation of anomeric derivatives has led to a search for means to eliminate this complication. The anomeric center may be removed either by conversion into the oxime5 or the nitrile,394,3943 by oxidation followed by formation of the lactone (see Section IX, p. 71), or by reduction to the alditol. The last method is simpler than oxidation, and the separation of alditols and of aldononitriles will be discussed here additional examples are given in Table V (see p. 119). The early work on the separation of alditols has been discussed by Bishop.4 The necessity of decomposing borate complexes... 

The Wohl degradation214 of suitably acetylated aldononitriles was used for the synthesis of 5-deoxy-L-arabinose,216 5-deoxy-D-lyxose,2W and 5-deoxy-D-ribose.217... 

B. A. Dmitriev, L. V. Backinowsky, O. S. Chizhov, B. M. Zolotarev, and N. K. Kochetkov, Gas-liquid chromatography and mass spectrometry of aldononitrile acetates and partially methylated aldononitrile acetates, Carbohydr. Res., 19 (1971) 432 135. 

Certain exceptions to this general scheme have been noted in which the normal hydrogenation of the nitrile group has not taken place. In these cases, a hydrolytic reaction has occurred, with the formation of an aldonic acid instead of the expected aldose.12 The anomalous reaction occurs when the nitrile exists in the (isomeric) iminolactone form for example, compound I is hydrolyzed directly, before hydrogenation can take place. This isomerism of the aldononitriles was established by Papadakis and Cohen,16 and the cyclic structure I was postulated by Wolfrom and coworkers.108... 

Zempl i, of aldononitriles, IV, 138 AVDehydroandrosterone, IV, 93 Dehydrocholic acid, IV, 106 Dehydrodesoxycholic acid, IV, 92 Dehydrohalogenation, of halo carbohydrates, III, 102 Density of cellulosic fibers, V, 121 Depolymerase, action on pectic acids, V, 82, 92... 

M. R. Cases, C. A. Stortz, and A. S. Cerezo, Separation and identification of partially ethylated galactoses as their acetylated aldononitriles and alditols by capillary gas chromatography and mass spectrometry,/. Chromatogr., 662 (1994) 293-299. 

Partially methylated, acetylated aldononitriles are acyclic derivatives readily formed from reducing sugars by reaction with hydroxylamine in pyridine, followed by the addition of acetic anhydride to effect elimination of acetic acid from oxime acetates and acetylation of unsubstituted hydroxyl groups. These derivatives, although less extensively used, appear to give good GLC separations, and their mass spectra can be readily interpreted without the problem of structural symmetry (75MI3). 

Poly-O-acetyl-benzothiazol-2-yl acyclo C-nucleosides 184 were prepared in good yields from the aldononitrile acetates (183) [69ACH(62)179 82ACH(109)229] or aldonoyl chloride acetates 38 [69ACH(62)179] by reaction with 2-aminothiophenols (Scheme 54). 

Single-peak sugar derivatives which allow the resolution of sugar constituents in pectin include the trimethylsilylated methyloximes (52), acetylated aldononitriles (53), trimethylsilylated alditols T54), and acetylated alditols (51.). A comprehensive review article on GLC of sugars has been published (26). 

Fig. 1 Schematic for the permethylation linkage analysis, exemplified by a hypothetical trisaccharidc, Gal-(a-l,4)-Glc-(a-l,6)-Man. The acid-hydrolyzed partially methylated monosaccharides generated are analyzed by GC-MS, typically as alditol or aldononitrile derivatives...

In this paper, we have compared two commonly used permethylation methods [4, 5] and have applied them to a model carbohydrate compound. The completeness of the methylation steps was established by matrix-assisted laser desorption/ionization tlme-of-flight mass spectrometry (MALDI-TOF MS). The methylated carbohydrate products were acid-hydrolyzed and converted to methylated partially acelylated aldononitrile derivatives (Me PAANs) for linkage analysis by gas chromatography-mass spectrometry (GC-MS) [11]. 

Reaction of per-O-benzoyl aldononitriles 712 with ammonium azide gave the tetrazole benzoate 713, whose debenzoylation gave 714. Other analogs with a different configuration were also prepared (79MI1). 

Cycloaddition of hydrazoic acid to aldononitriles (618) (71MI2 75MI5 79MI13 90MI3) or thermolysis of the 1,1-diazido acyclic sugar derivatives 789 [95JCS(P1)1747] yielded the tetrazole acyclo C-nucleosides 749 (Scheme 218). 

Aldononitrile acetates are suitable for analysis of sugars by g-l.c., and give characteristic mass spectra that are easy to interpret. The molecular ion is not seen, but ions are found at (M — 73) and (M — 98) , corresponding to loss of CH2OAC and CH(OAc)CN moieties, respectively. Primary fragments are formed by a-cleavage of the alditol chain, as depicted in 40. The ions m/e 98 and 170, expected from fission... 

Secondary fragments were formed by single or consecutive eliminations of acetic acid or ketene, as already described (see Section IV,1 p. 53). Partially methylated aldononitrile acetates have been investigated by Kochetkov and coworkers. They found that this class of compounds is fragmented in a manner analogous to that described for partially methylated alditol acetates (see Section IV,5 p. 58). 

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