Apiose

Carbohydrates that have a carbon substituent attached to the mam chain are said to have a branched chain d Apiose and l vancosamme are representative branched chain carbohydrates... 

The Fischer projection of the branched chain carbohydrate D apiose has been presented in Section 25 12... 

Hydroxymethyl)-D-g/ycero-tetrose Note. For the cyclic forms of apiose, systematic names are preferred, e.g. 

Fig. 5 Presentation of the 3D organisation of the RG-II dimer in which two apioses are cross-linked by a 1 2 borate-diol ester, as proposed by Perez et al. [23]...

Fig. 18.—Sequence of Heptasaccharide Isolated from RG-II. [Fragment-ions of the deuteropermethylated derivative are shown. Cleavages are all of the A, Type. (Rha = rhamnose, Ara = arabinose, AceA = aceric acid, MeFuc = 2-0-methylfucose, and Api = apiose).]...

Isomers of D-apiofuranosyl 1-phosphate have been prepared by treating a mixture of jS-o-apio-D-furanosyl and /3-D-apio-L-furanosyl tetra-acetates with crystalline phosphoric acid. a-o-Apio-o- (59) and a-o-apio-L-furanosyl-1-phosphate (60) and their cyclic phosphates were separated by chromatography and identified by H n.m.r. o-Apiose is metabolized in parsley and Lemna minor with the possible formation of UDP-D-apiose. L. minor will convert UDP-a-glucuronic acid into a-o-apio-D-furanosyl-1,2-cyclic phosphate (61) but no evidence of UDP-o-apiose was found, although it is possible that (61) arose from the rapid hydrolysis of UDP-o-apiose. 

The glycosyl-residue compositions of the three purified fractions (Table 1) were very similar with a predominance of galacturonic acid, rhamnose and arabinose. The presence in the three purified fractions of the rare monosaccharides characteristic of RG-II (e.g. 2-( -methyl-L-fucose, 2-O-methyl-D-xylose, apiose, Kdo, Dha and aceric acid) was confirmed by GC-CIMS analysis. The molar ratios corresponded approximately to the known structure of the RG-II molecule (Figure 1) and to previously published data for RG-II from sycamore [26], rice [4], arabidospis leaves [8] and Pectinol [12]. 

It has been suggested15 that apiose [3-(hydroxymethyl)-D-g cero-tetrose] (LVII), a branched-chain pentose,47 originates from the aldol reaction of dihydroxyacetone with glycolaldehyde. The origin of this and all other branched-chain sugars so far encountered in natural products is uncertain, but they may arise from intermediate branched-chain carboxylic acids which are believed to be formed in the fixation of carbon dioxide (see above). 

---