Rhamnosylation

Because of this situation, the prospect of synthesizing D-rhamnosyl cardenolides containing the unnatural, a-D-linkage was investigated. D-Rhamnose has not been reported to occur naturally, but it has been synthesized by Hudson and co-workers (4) in six steps, starting with methyl a-D-mannopyranoside. An intermediate in the synthesis is methyl... 

Neohesperidin dihydrochalcone 2-O-a-L-rhamnosyl- -D-glucopyranoside substituted phloroglucinol, -QH, substituted phloroglucinol, -C2H4 phenyl OH and —OMe... 

Most of the anthocyanins acylated with caffeic acid have this cinnamyl moiety linked to a glucosyl position 6, as in gooseberries, some grape cultivars, ° " ° black carrots, red cabbage,red radishes," and sweet potatoes. Some anthocyanins isolated from species of potatoes have a caffeyl group located at position 4 of the rhamnosyl unit of the rutinose disaccharide. " ... 

Extrapolated to the pectic backbone, the present findings support previous descriptions concerning the stuctural role that may be ascribed to the presence of rhamnosyl units. When smooth homogalacturonan regions are interspersed with hairy rhamnogalacturonan regions there is no major effect on the extension and the orientation of the pectic polysaccharide. 

Calogero and Di Marco used the red antioxidant cyanidine-3-glucoside and a mixture of cis and trans isomers ofdelphinidin 3-[4-(p-coumaroyl)-L-rhamnosyl-(l-6)-glucopyranoside]-5-glucopyranoside (Figure 9.4), extracted from the red Sicilian... 

Analysis of S23 showed that it is composed52 of residues of L-rhamnose (35), D-galactose (31), and D-glucose (32%). Some phosphorus (3%) was also found. Immunochemical studies indicated that the polymer contains terminal L-rhamnosyl groups. 

Figure 6.1 Major branch pathways of flavonoid biosynthesis in Arabidopsis. Branch pathways, enzymes, and end products present in other plants but not Arabidopsis are shown in light gray. Abbreviations cinnamate-4-hydroxylase (C4H), chalcone isomerase (CHI), chalcone synthase (CHS), 4-coumarate CoA-ligase (4CL), dihydroflavonol 4-reductase (DFR), flavanone 3-hydroxylase (F3H), flavonoid 3 or 3 5 hydroxylase (F3 H, F3 5 H), leucoanthocyanidin dioxygenase (LDOX), leucoanthocyanidin reductase (LCR), O-methyltransferase (OMT), phenylalanine ammonia-lyase (PAL), rhamnosyl transferase (RT), and UDP flavonoid glucosyl transferase (UFGT).

An efficient synthesis of the pyruvated repeating unit of the exo-polysaccharide of Streptococcus pneumoniae containing a P-linked L-rhamnosyl moiety was also... 

When grown at 25°, mycelia, or conidia mixed with mycelia, produce di-O-rhamnosyl side-chains (see the preceding) that are the main, antigenic determinants, as shown by inhibition experiments with oligosaccharides and rabbit immune serum.131 The response of human sera to the polysaccharide, and the fact that 13C-n.m.r. spectroscopy showed that conidia of S. schenckii form a rhamnomannan similar to the yeast component and different from the di-O-rhamnosylman-nan of hyphae,132 suggest the formation of hyphae in vivo. 

YCV 37 mixed (yeasts predominating) S monorhamnosylmannan having a small proportion of di-rhamnosyl side-chains... 

Fig. 20.—l3C-N.m.r. Spectra of Glucosyluronorharrmomannan of Ceratocystis steno-ceras (A), and the Acid-Degraded Product Lacking Rhamnosyl End-Units (B). Solvent, D20 temperature, 70° chemical shifts expressed as 8C, relative to external tetramethyl-silane.)... 

Signals of rhamnomannans and acidic rhamnomannan were assigned as follows. The C-l resonances of mono- and di-rhamnosyl side-chains were determined by comparison with those of 3-O-a-L-rhamnopyranosyl-a-D-mannose (C-l, 98.0) and O-a-L-rhamnopyrano-syl-(l— 2)-0-o -L-rhamnopyranosyl-(l—>3)-a-D-mannose (C-l", 103.7 C-l, 96.8). C-l signals of the main chain should be similar in shift to that12 of an unsubstituted, a-D-( 1— 6)-linked D-mannopyranan, Sc... 

Table 6.3 Biochemical properties of Citrus flavanone 7-O-Glucoside, 2"-0-Rhamnosyl-...

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