Trisaccharides structure

Aurantoside C from the Philippinian sponge Homophymia conferta differs from aurantoside A (21) and B (22) in polyene chain length and in the trisaccharide structure and is mildly toxic to brine shrimp (LC50 50 pg/ml) [139]. 

It may be seen that only several elements of the trisaccharide structure seem to be strictly controlled by the specificity of the enzymes. These include the anomeric configuration of the terminal monosaccharide residue of the glycosyl acceptor and the configuration of C-4 of the D-mannopyranosyl... 

Further studies by methylation analysis, n.m.r. spectroscopy, circular dichroism, and m.s. on the gentamicins demonstrated the trisaccharide structure 55 for these aminocyclitol antibiotics. The m.s. studies of these compounds as N-acetylated and permethylated derivatives provided the molecular weight and sequential order of the monosaccharide residues. M.s. studies have also been made on these and other aminocyclitol antibiotics (tobramycin and kanamycin) without prior derivatization. ... 

Structure of xanthan has been determined by chemical degradation and methylation analysis (335,336) it is composed of repeating units consisting of a main chain of D-glucopyranosyl residues with trisaccharide side chains made up of D-mannopyranosyl and D-glucopyranosyluronic acid residues. 

Hen egg-white lysozyme catalyzes the hydrolysis of various oligosaccharides, especially those of bacterial cell walls. The elucidation of the X-ray structure of this enzyme by David Phillips and co-workers (Ref. 1) provided the first glimpse of the structure of an enzyme-active site. The determination of the structure of this enzyme with trisaccharide competitive inhibitors and biochemical studies led to a detailed model for lysozyme and its hexa N-acetyl glucoseamine (hexa-NAG) substrate (Fig. 6.1). These studies identified the C-O bond between the D and E residues of the substrate as the bond which is being specifically cleaved by the enzyme and located the residues Glu 37 and Asp 52 as the major catalytic residues. The initial structural studies led to various proposals of how catalysis might take place. Here we consider these proposals and show how to examine their validity by computer modeling approaches. 

Total synthesis of (+)-validamycins A and B starting from a common synthetic intermediate was elaborated by the following sequence. Tetra-(9-benzyl-(-l-)-valienamine (370), derived from 211, and the di-O-benzyl derivative (371) of the epoxide were coupled in 2-propanol to produce the protected dicarba compound (374), the structure of which was confirmed by conversion into (-1-)-validoxylamine B nonaacetate. Concurrently, compound 372 was glycosylated and the product oxidized with a peroxy acid, to afford a mixture of products from which the desired epoxide (373) was obtained in 70% yield. Coupling of 370 with 373 in 2-propanol at 120° afforded two carba-trisaccharides, and the major product (47%) was depro-tected and characterized as the dodecaacetate of validamycin B. The pro-... 

The first heteropolysaccharide for which a cyclic structure has been proposed is the enterobacterial common antigen (ECA), which was shown by f.a.b.-m.s. to be a mixture of three cyclic components containing 4, 5, and 6 repeats, respectively, of a previously characterized trisaccharide (31) in which the GlcNAc residues were known to be partially acetylated at 0-6. 

The establishment of the structure of turanose furnishes a firm basis for an eventual determination of the structure of melezitose. One can start with the assurance that the trisaccharide is 8-[a-v-glucopyranosyVy D-fructose < > n-glucopyranose this formula requires three further specifications. The first of these is an allocation of a ring to the fructose unit, the second is a decision between the a- and /S-forms for this unit, and the third is a similar decision between these forms for the right-hand D-glucopyranose unit. Decision on these three matters can be made readily if sucrose should ever be found to result from a partial hydrolysis of melezitose, because sucrose is almost certainly f)-v-fructo-... 

The presence of the pyranose ring in the two D-glucose units of melezitose was inferred by Zempl6n and Braun from good evidence, and made certain by Miss Leitch29 through the crystallization of the requisite amount of 2,3,4,6-tetramethyl-D-glucose from the scission products of the fully methylated trisaccharide. The revised interpretation of Miss Leitch s experimental data concerns only the structure of the... 

F. Alberto, E. Jordi, B. Henrissat, and M. Czjzek, Crystal structure of inactivated Thermotoga maritima invertase in complex with the trisaccharide substrate raffinose, Biochem. J., 395 (2006) 4574-62. 

Baddiley and coworkers42 have studied the structure of S13, which is composed of D-galactose, D-glucose, 2-acetamido-2-deoxy-D-glucose, and ribitol residues, and phosphate groups in the molar proportions 2 1 1 1 1. O-Acetyl groups are also present. A neutral pentasaccharide was obtained by hydrolysis with alkali, followed by enzymic dephosphorylation. On mild, acid hydrolysis, this yielded two main products, a trisaccharide (19) and a disaccharide (20), the structures of which were determined by conventional methods. 

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