L-Arabino

The L-arabino-(4-0-methyl-D-glucurono)xylans are found in softwoods and annual plants. The L-arabinose is present primarily as a-L-arabinofuranosyl units, although P-L-arabinopyranosyl units may also be present. In either case, the arabinosyl units are often, but not always, present as single-unit side chains, as are the uronic acid units. 

Acetyl-5-deoxy-5-iodo-l, 2-O-isopropylidene-p - l - arabinofuranose (38). Acetylation of 5-deoxy-5-iodo-l,2-0-isopropylidene-/ -L-arabino-furanose (37) (27) in pyridine as described above for the D-xylo-isomer afforded the 3-acetate (38) as a colorless sirup which did not crystallize. [ ]D24 + 13.7° (c, 3.5). Anal Calcd. for C10H15IO5 C, 35.1 H, 4.4. Found C, 35.0 H, 4.5. 

From 1,2-0-isopropylidene-3,5-di-0-tosyl-/ -d-xylofuranose (21) (29). Treating 29 with silver fluoride in pyridine and isolating as described above for the l-arabino isomer gave a 40% yield of 32 after a reaction time of 48 hours. The product had [ ]D25 — 14.9° and had an infrared spectrum identical with material prepared as above. 

Other trivial names that have been used include ascarylose for 3,6-dideoxy-L-arabino-hexose, colitose for 3,6-dideoxy-L-ry/o-hexose and paratose for 3,6-dide-oxy-D-rifeo-hexose. 

Fig. 3 Primary structure of (L-arabino)-4-0-methyl-D-glucurono-D-xylan (AGX)...

Fig. 5 Primary structure of water-soluble L-arabino-D-xylan (AX)...

S-glycofuranosyl dithiocarbamates with 5-nitro-2-pyridyl 2,3,4-tri-O-benzoyl-l-thio-P-D-glucopyranoside as an acceptor gives access to valuable 1,2-ds-linked furanosyl-1-thiopyranosides [498]. Recently, Bogusiak reported that perbenzylated S-benzothiazolyl glycosides of L-arabino, D-ribo and D-xylofuranose can be used as glycosyl donors (Scheme 4.91). ... 

Zemplen s work was revisited by Bromund et al43 by exploring the reaction in diverse aldose series (D-galacto, D-xylo, L-arabino). Similar bicyclic fused structures of OZT on pyran backbones were proposed (Scheme 20). 

The second important group of hemicelluloses found in softwoods are the arabino-(4-0-methylglucurono)xylans, which may make up from 5 to 10% of the dry weight of the wood. These consist of /3-1,4-linked D-xylopyranose units, partially substituted by L-arabino-furanose (at the 3 position) and by 4-O-methyl D-glucuronic acid (at the 2 position). The frequency of these substituent groups is around 1 to 2 residues per 10 xylose units. 

Information on the linkage requirements (for arabinofuranosidase) and the subsite binding requirements of em/o-arabinanase was obtained by studying the kinetics of hydrolysis of 1,5-a-L-arabino-oligosaccharides (compared to beet arabinan) and by characterising the structures of the branched arabino-oligosaccharides produced by endo-arabinanase hydrolysis of partiaUy debranched beet arabinan. With arabinofuranosidase, the rates of hydrolysis of... 

Table II. Kinetic constants for. niger a-L-Arabino-furanosidase on Arabinotriitol and Sugar-Beet Arabinan...

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