3-Deoxy-2-keto acids formation

Labeling experiments with l-deoxy-l-(dibenzylamino)-D-[l- C]-aruI>-mo-2-hexulosuronic acid [l- C] 112 indicated that the C label corresponded to the 5-methyl group of 111 (see Ref. 234). This is also consistent with a l-deoxy-2,3-dicarbonyl intermediate (115), and indicates that 111 is a decarboxylation product (see Scheme 22). The precise step entailing decarboxylation has not yet been determined. The carboxyl group could be carried through to ring closure (furanone formation). Such a step would provide a 2-carboxylate which is a /3-keto acid subject to ready decarboxylation. The labeling information and the initial steps of the mechanism in Scheme 22 are also consistent with the formation of 111 from D-[l- C]ribose and a secondary amine. ... 

I, 7-diphosphate.170 1 (f> This tetrose phosphate is involved with phosphoenol pyruvate in the formation of shikimic acid via 3-deoxy-2-keto-D-ara6ino-heptonic acid 7-phosphate and, hence, of aromatic compounds.170(d) A synthesis of the tetrose phosphate has been described.170 1 Aldolase shows a high affinity for the heptulose diphosphate and, compared with that for D-fructose 1,6-diphosphate, the rate of reaction is about 60 %. The enzyme transaldolase, purified 400-fold from yeast, catalyzes the following reversible reaction by transfer of the dihydroxyacetonyl group.l70(o>... 

This section deals with acids, that are formally modified aldonic acids, such as keto, deoxy, and branched-chain acids (including the so-called saccharinic acids). The aminoaldonic acids, which are oxidation products of amino sugars, and, in particular, the important nonulosaminic acids (neuraminic acids) and muramic acid, are not discussed here. The formation of saccharinic acids by the treatment of sugars with alkali, and the mechanisms involved, are likewise outside the scope of this chapter. 

Other Aldolases. In addition to the DHAP aldolases, we have conducted preliminary investigations of two other aldolases. KDO synthase (E.C. 4.1.2.16) catalyzes the formation of 2-keto-3-deoxy-L-nrahi/io-octulosonic acid 8-phosphate (KDO-8-P) from arabinose 5-phosphate and PEP (Scheme 10) (29). KDO is an integral component of Gram-negative bacterial cell walls, and derivatives of KDO are of interest as inhibitors of cell wall formation (30, 31). 

YerE was found to be even more promising. It is an enzyme involved in the biosynthetic pathway of Yersinose A, a branched-chain 3,6-di(deoxy)hexose. It catalyzes the ThDP-dependent coupling of pymvate with cytidine-5 -diphosphate-3,6-di(deoxy)-4-keto-D-glucose. The amino-acid sequence of YerE was found to be very similar to the large subunit of Escherichia coli AHAS (EcAHAS). Furthermore, as for AHAS, YerE was found to suppress the formation of acetolactate in favor of (/ )-PAC. The scope of this new... 

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