Rhamnopyranose

Table 3 Comparison of an L-rhamnopyranose and L-rhamnofuranose as glycosidases percentage inhibition at 1 mM <1999T4489, 1996TL8565>...

C6H1205 H20 6-Deoxy-a-L-mannopyranose monohydrate a-L-rhamnopyranose monohydrate (RHAMOH02)32... 

Since A = 50.0 —> 64.7, only small quantities of furanoses can be present and the transition of the pyranoses is hardly disturbed. Accordingly the common or a-L-rhamnose is the imns-L-rhamnopyranose. 

Notes pg, pelargonidin cy, cyanidin dp, delphinidin pn, peonidin pt, petunidin mv, malvidin all, allopyranose ara, a-arabinopyranose gal, galactopyranose glc, glucopyranose glu, glucuronic acid rha, rhamnopyranose xyl, xylopyranose ac, acetyl benz, benzoyl caf, caffeoyl cin, cinnamoyl cou,/>-coumaroyl fer, feruloyl gall, galloyl mal, malonyl sinap, sinapoyl ND, not detected. 

Notes all, allopyranose ara, arabinopyranose gal, galactopyranose glc, glucopyranose glu, glucuronic acid rha, rhamnopyranose xyl, xylopyranose ac, acetyl mal, malonyl t, terminal. 

Quite analogous ring-closures occur when the 1-O-acetyl derivatives of the rhamnopyranose and talopyranose derivatives are treated with sodium azide in N,N-dimethylformamide. l-O-Acetyl-6-deoxy-2,3-0-isopropylidene-4-0-mesyl-a-L-mannopyranose is converted exclusively into l,4-anhydro-6-deoxy-2,3-0-isopropylidene-/3-L-talo-pyranose. In this instance, the azide nucleophile attacks the l-O-ace-tyl group, liberating an 0-1 oxide ion which reacts with inversion of C-4. The 4-epimeric, l-O-acetyl-6-deoxy-talose derivative gives 60% of the direct inversion product l,4-anhydro-6-deoxy-2,3-0-isopropyli-dene-a-L-mannopyranose, together with other products.50... 

The same compounds isolated by Brigl and coworkers,9 who started from 2,3,4,5,6,7-hexa-O-benzoyl-D-gZt/cero-D-gaZacto-heptononitriIe, were obtained from the ammonolysis of 1,2,3,4,6-penta-O-benzoyl-a-D-mannose,19 namely, a mixture of l,l-bis(benzamido)-l-deoxy-D-mannitol (12) and N-benzoyl-D-mannopyranosylamine (13). Likewise, 1,2,3,4-tetra-O-benzoyl-L-rhamnopyranose,10 having the same steric relationship at the asymmetric carbon atoms as the perbenzoate of D-mannose, also afforded an N-benzoyl-L-rhamnopyranosylamine directly. 

The higher yield of the pyranose derivatives (see Table II) in the ammonolysis of a,/3-L-rhamnopyranose tetraacetate shows the influence of polar effects, because the methyl substituent on C-5 would enhance the nucleophilic character of its hydroxyl group in relation to that of the one on C-4. 

Fleet and co-workers (75a) synthesized various tetrazoles from manno- and rhamnopyranoses, as well as furanoses, based on the intramolecular 1,3-dipolar cycloadditions of azides with nitriles (Scheme 9.75). All of these tetrazoles were tested for their inhibitory activities toward both glycosidases and other sugarprocessing enzymes. D-Mannopyranotetrazole (397) was prepared from L-gluono-lactone (393). Azide 394 on ring opening with ammonia followed by dehydration with trifluoroacetic anhydride gave the azido nitrile 395. Intramolecular 1,3-dipolar cycloaddition of 395 in refluxing toluene followed by deprotection produced the D-mannopyranotetrazole 397 in 86% overall yield. 

Approximately 400 different glycosyltransferases are necessary in order to ensure the synthesis of those bacterial polysaccharides whose structures have thus far been elucidated. This estimate is based on the results of an analysis of the structures, made in order to ascertain how many different disaccharide fragments are present. An example of such an analysis is shown in Table V for the disaccharide sequences L-rhamnopyranosyl-D-galacto-pyranose, D-mannopyranosyl-L-rhamnopyranose, and D-galactopyranosyl-D-mannopyranose that are characteristic for the O-specific polysaccharides of Salmonella serogroups A, B, D, and E, the objects of many biosynthetic studies. Full details of similar analyses for other disaccharide sequences will be published elsewhere, as the resulting Tables are too voluminous for inclusion in this Chapter, but the most interesting results are summarized in Tables VI and VII. 

Q. Chen, F. Kong, and L. Cao, Synthesis, conformational analysis and the glycosidic coupling reaction of substituted 2,7-dioxabicyclo[4.1.0]heptanes l,2-anhydro-3,4-di-O-benzyl-/i-i - and /fn-rhamnopyranoses, Carbohydr. Res., 240 (1993) 107-117. 

S.-Q. Xiong, F.-Z. Kong, C.-J. Yang, Improved synthesis of l,3-anhydro-2,4-di-0-benzyl-/1-L-rhamnopyranose and l,3-anhydro-2,4,6-tri-0-benzyl-/l-D-mannopyranose. Youji Huaxue, 14 (1994) 280-285 Chem. Abstr., 121 (1994) 205804. 

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