KDO

The related 3-deoxy-D-waHnooctulosonic acid aldolase (KDO aldolase F.C 4.1.2.23) likewise suffers from an unattractive equilibrium constant but allows a simple synthesis of specifically labelled KDO from D-arabinose and labelled pyruvate28. 

Deoxy-i>maw f)-2-octulosonic acid 8-phosphate can be obtained in gram quantities by using KDO synthase (F.C 4.1.2.16) for the addition of PEP to D-arabinose 5-phosphate33. DA HP synthase (EC 4.1.2.15) produces 3-deoxy-L>-arer/>/>io-heptulosonic acid 7-phosphate from PEP and D-erythrose 4-phosphate35. 

Note, The last of the above examples is one of the possible forms of the compound referred to by the three-letter symbol Kdo (formerly the abbreviation KDO, from the previously allowed trivial name ketodeoxyoctonic acid). Similarly the symbol Kdn for the C9 sugar 3-deoxy-D-g/ycero-D-gaiacro-non-2-ulopyranosonic acid is widely used. 

Already in 1988 and 1991, Gao et al. [65,66] detected four different polysaccharides present in the leaves of Panax ginseng that had an effect on the complement system, but only two of them, the neutral, GL-NIa, and one of the acidic ones, GL-AIa, had potent activities at low concentrations. GL-NIa was found to be mainly an arabinigalactan type II polymer. GL-AIa was a polysaccharide with a rhamnogalacturonan core with neutral side chains of the AG-II type, confirmed by a strong reaction with the Yariv reagent and the methylation results. It was shown that the crude polysaccharide fraction contained KDO and DHA, suggesting the presence of Rhamnogalacturonan II in... 

Pyruvate-dependent lyases serve catabolic functions in vivo in the degradation of sialic acids and KDO (2-keto-3-deoxy-manno-octosonate), and in that of 2-keto-3-deoxy aldonic acid intermediates from hexose or pentose catabolism. 

As an example for continuous process design, 2-keto-3-deoxy-D lycero-D-galacto-nonosouate (KDN) (S) has been produced on a 100-g scale from D-mannose and pyruvate using a pilot-scale EMR at a space-time yield of 375 gl d and an overall crystallized yield of 75% (Figure 10.6) [47]. Similarly, L-KDO (6) can be synthesized from L-arabinose [48]. 

The KDO aldolase (KdoA, EC 4.1.2.23) is involved in the catabolism of the eight-carbon sugar d-KDO, which is reversibly degraded to D-arabinose (15) and pyruvate (Figure 10.10). The enzyme has been partially purified from bacterial sources and studied for synthetic applications [71,74]. It seems that the KdoA, similar to... 

NeuA, has broad substrate specificity for aldoses while pyruvate was found to be irreplaceable. As a notable distinction, KdoA was also active on smaller acceptors such as glyceraldehyde. Preparative applications, for example, for the synthesis of KDO (enf-6) and its homologs or analogs (16)/(17), suffer from an unfavorable equilibrium constant of 13 in direction of synthesis [34]. The stereochemical course of aldol additions generally seems to adhere to a re-face attack on the aldehyde carbonyl, which is complementary to the stereoselectivity of NeuA. On the basis of the results published so far, it may be concluded that a (31 )-configuration is necessary (but not sufficient), and that stereochemical requirements at C-2 are less stringent [71]. 

Figure 10.22 Synthetic approaches to DAHP and KDO by a backbone inversion strategy using FruA cataiysis.

The biosynthesis of Kdo and neuraminic acid is known to involve enol-pyruvate phosphate and D-arabinose or 2-acetamido-2-deoxy-D-mannose, respectively. Nothing is known about the biosynthesis of all the other glycu-losonic acids. One interesting problem is, for example, whether the two 5,7-diamino-3,5,7,9-tetradeoxynonulosonic acids are synthesized analogously to neuraminic acid, from a three- and a six-carbon fragment, by modification of neuraminic acid on the sugar nucleotide level, or by a third, less obvious route. 

RG-II [5] proportion of common and rare sugars like Ome-xylose, KDO, DHA number, type and distribution of uronic acids in the (side) chain attachment and distribution of RG-II chains over the pectic molecule presence and position of ferulic acid ... 

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]. 

Dha and Kdo being destroyed under the acidic conditions used to cleave glycosidic linkages [11] their methyl ethers could not be analyzed in this study. 

RG-n, Rhamnogalacturonan II Kdo, 3-deoxy-D-manno-octulosonic acid Dha, 3-deoxy-D-/yxo-heptulosaric acid aceric acid, 3-C- carboxy-5-deoxy-L-xylose TMS, per-0-trimethylsilylated methyl glycosides. 

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