Aldoses, structure

Methylation of Monocarboxylic Acids Derived from Aldoses. Structure of Pentamethyl a-Gluco-heptono-y-lactone, W. N. Haworth, E. L. Hirst, and M. Stacey, J. Chem. Soc., (1932) 2481-2485. 

Fig. 4 a a-D-glucose in the pyranose form, b a-D-ribose in the furanose ring form, c aldose structure of D-glucose, and d aldose stracture of D-ribose... 

Aldoses exist almost exclusively as their cyclic hemiacetals very little of the open chain form is present at equilibrium To understand their structures and chemical reac tions we need to be able to translate Fischer projections of carbohydrates into their cyclic hemiacetal forms Consider first cyclic hemiacetal formation m d erythrose To visualize furanose nng formation more clearly redraw the Fischer projection m a form more suited to cyclization being careful to maintain the stereochemistry at each chirality center... 

Aldonic acid (Section 25 19) Carboxylic acid obtained by oxi dation of the aldehyde function of an aldose Aldose (Section 25 1) Carbohydrate that contains an aldehyde carbonyl group in its open chain form Alicyclic (Section 2 15) Term describing an a/iphatic cyclic structural unit... 

FIGURE 7.1 Structure of a simple aldose (glyceraldehyde) aud a simple ketose (dihy-droxyacetoue). 

FIGURE 7.2 The structure and stereochemical relationships of D-aldoses having three to six carbons. The configuration in each case is determined by the highest numbered asymmetric carbon (shown in gray). In each row, the new asymmetric carbon is shown in red. 

In addition to the common carbohydrates mentioned in previous sections, there are a variety of important carbohydrate-derived materials. Their structural resemblance to sugars is clear, but they aren t simple aldoses or ketoses. 

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

Uridine, biosynthesis of, 1124 Uronic acid, 994 from aldoses, 994 Urushiols, structure of, 600 UV, see Ultraviolet... 

Stacey started research in an inspiring and stimulating atmosphere that he strove to maintain, add to, and develop when it became his turn to lead the department. His earliest research was with Haworth and his key partner E. L. Hirst [Adv. Carbohydr. Chem. Biochem., 35 (1978) 1 -29] on aspects of the chemistry of glucoheptose. His first publication with them in 1931 was entitled Walden Inversion in the a-Glucoheptose Series, followed in the next year by a report on the methylation of monocarboxylic acids derived from aldoses and the structure of pentamethyl a-gluco-heptonolactone. He found this to be a difficult project because, initially, he could not crystallize his stock of glucoheptose. Then, as later, he found crystallization to be a challenging problem. 

The basis for the name is the structure of the parent monosaccharide in the acyclic form. Charts I and IV (2-Carb-10) give trivial names for parent aldoses and ketoses with up to six carbon atoms. 2-Carb-8.2 and 2-Carb-10.3 describe systematic naming procedures. 

Chart I. Trivial names (with recommended three-letter abbreviations in parentheses) and structures (in the aldehydic, acyclic form) of the aldoses with three to six carbon atoms. Only the D-forms are shown the L-forms are the mirror images. The chains of chiral atoms delineated in bold face correspond to the configurational prefixes given in italics below the names... 

A more general access to biologically important and structurally more diverse aldose isomers makes use of ketol isomerases for the enzymatic interconversion of ketoses to aldoses. For a full realization of the concept of enzymatic stereodivergent carbohydrate synthesis, the stereochemically complementary i-rhamnose (Rhal EC 5.3.1.14) and i-fucose isomerases (Fuel EC 5.3.1.3) from E. coli have been shown to display a relaxed substrate tolerance [16,99,113,131]. Both enzymes convert sugars and their derivatives that have a common (3 J )-OH configuration, but may deviate in... 

Iwata Y, Arisawa M, Hamada R, Kita Y, Mizutani MY, Tomioka N, Itai A, Miyamoto S. Discovery of novel aldose reductase inhibitors using a protein structure-based approach 3D-database search followed by design and synthesis. J Med Chem 2001 44 1718-28. 

The results of inhibition studies with aldonolactones and 5-amino-5-deoxyaldonolactams may be summarized as follows y -D-glycosidases are inhibited by 1,5-lactones and the lactams some 100- to > 10,000-fold better than by the parent aldoses, with Kj values from 200 //Mto <0.1 nM. Al-dono-1,4-lactones are probably no better inhibitors than aldoses or polyols of comparable structure, with the possible exception s of 2-acetamido-2-deoxy-D-glucono-1,4-lactone. 

Aldose-ketose isomerism Fructose has the same molecular formula as glucose but differs in its structural formula, since there is a potential keto group in position 2, the anomeric carbon of fmctose (Figures 13 and 13-7), whereas there is a potential aldehyde group in position 1, the anomeric carbon of glucose (Figures 13-2 and 13-6). 

Morikawa, T. Kishi, A. Pongpiriyadacha, Y. Matsuda, H. Yoshikawa, M. Structures of new friedelane-type triterpenes and eudesmane-type sesquiterpene and aldose reductase inhibitors from Salacia chinensis. J. Nat. Prod. 2003, 66, 1191-1196. 

Reducing sugars can be detected by reaction with phenylhydrazine to yield a hydrazone product, except the result of the reaction is not what one might imagine giving the structure of aldoses and ketoses. Glucose, for example, can react with phenylhydrazine to yield the anticipated... 

The reaction of ethyl acetoacetate with simple hydroxy ketones has been compared with the corresponding reactions of the ketoses. The results obtained with l-hydroxy-2-propanone and 3-hydroxy-2-butanone, under the same experimental conditions as with D-fructose, establish a parallel between these reactions. However, as in the case of the aldoses, the yield is greater for these simpler hydroxy ketones than for the ketoses.9 The resultant esters, (XV and XVI), were obtained in the form of sirups, but the free acids, (XVII and XVIII), and their phenacyl esters are crystalline. The acids were shown to be identical with those of known structure described in the literature.9... 

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