3- Deoxy-glyceraldehyde, derivatives

Further, the olefinic alcohols (11a and 11b) derived from an (l )-glyceraldehyde derivative, upon PdCl2- and Pd(OAc)2-mediated cyclization, gave hitherto important 2-deoxy C-alkyl (12) and C-vinyl glycosides (13), respectively, albeit as 1 1 mixtures, due to the absense of anchimeric assistance in stereodefining (Scheme 22.4). 

L-Ribose is quite rare and the only practical method for its preparation is the transformation of L-arabinose by the method of Austin and HumoUer (4 steps, 9.5 % overall yield). L-Ribose has also been derived from, 2,3-<9-isopropylidene-L-glyceraldehyde, (5 steps, 12 %) after separation from a mixture containing L-arabinose. In Scheme 7 we summarize our total syntheses of D- and L-ribose derivatives using the " naked sugars" 32 and 38, respectively." Ketone 138 (Scheme 4) was oxidized into the corresponding lactone (-)-158 with MCPBA in 98 % yield. Treatment with anhydrous methanol, 2,2-dimethoxypropane and a small amount of methanesulfonic acid afforded the methyl 5-deoxy-D-allonate (-)-I59... 

Finally, the 3-deoxy-D-threo-2-hexulosonate was split291 by an aldolase into pyruvate and 3-deoxy-D-glyceraldehyde, the L-arabino derivative being a rather better substrate than that derived from D-fucose. 

Deoxy-D-xylulose is a known natural product. It was first isolated from the fermentation broth of a Streptomyces and later shown to be a precursor of pyridoxol. Its structure can be deduced biogenetically from pyruvate and glyceraldehyde phosphate (Figs. 2 and 3). Two H-labeled DX isotopomers were synthesized chemically. They were incorporated efficiently into the prenyl chains of ubiquinone and menaquinone by wild-type E. coli, indicating that a DX derivative is an isoprenoid precursor (2, 3). 

Mukaiyama and coworkers have pioneered many routes to the total syntheses of rare carbohydrates such as the 2-amino-2-deoxypentoses [75]. In 1982, they reported that the potassium enolate derived from the magnesium salt of the (/ )-atrolactic acid derivative 85 adds to 2,3-0-isopropylidene-D-glyceraldehyde in a highly stereoselective manner giving, after alcohol protection, imine hydrolysis and amine protection, the D-arabinopentoate derivative 86 (Scheme 13.35). Further elaboration leads to 2-acetamido-2-deoxy-D-arabinose 87. In a similar fashion, starting from (5 )-atrolactic acid, 2-acetamido-2-deoxy-D-ribose 88 was prepared [76]. 

The periodate cleavage of 2- or 4-O-substituted derivatives of 1,6-anhydro-/3-D-hexopyran oses provides the possibility134,194,383,464 of preparing partially substituted derivatives of D- or L-glyceraldehyde, 2-O-substituted derivatives of D-erythrose or D-threose, and other useful compounds. Attempts to condense the dialdehydes resulting from 2-deoxy, 4-deoxy, and 2-acetamido-2-deoxy derivatives of 1,6-anhydro-... 

Terpenoids do not necessarily contain exact multiples of five carbons and allowance has to be made for the loss or addition of one or more fragments and possible molecular rearrangements during biosynthesis. In reality the terpenoids are biosynthesized from acetate units derived from the primary metabolism of fatty acids, carbohydrates and some amino acids (see Fig. 2.10). Acetate has been shown to be the sole primary precursor of the terpenoid cholesterol. The major route for terpenoid biosynthesis, the mevalonate pathway, is summarized in Fig. 2.16. Acetyl-CoA is involved in the generation of the C6 mevalonate unit, a process that involves reduction by NADPH. Subsequent decarboxylation during phosphorylation (i.e. addition of phosphate) in the presence of ATP yields the fundamental isoprenoid unit, isopentenyl pyrophosphate (IPP), from which the terpenoids are synthesized by enzymatic condensation reactions. Recently, an alternative pathway has been discovered for the formation of IPP in various eubacteria and plants, which involves the condensation of glyceraldehyde 3-phosphate and pyruvate to form the intermediate 1-deoxy-D-xylulose 5-phosphate (Fig. 2.16 e.g. Eisenreich et al. 1998). We consider some of the more common examples of the main classes of terpenoids below. 

Several amino-sugar syntheses have employed 3- and 4-carbon chiral starting materials. 2,3- -Isopropylldene-D-glyceraldehyde (34) has been elaborated into the 3-acetamido-2,3-dldeoxy-pyrano-side (35) and the 3-nitro-furanoslduronlc acid (36) by stereoselective allylation of the nitronate dlanlon derived from nltro derivative (37) (Scheme 11) and into 2-amlno-2-deoxy-D-arabinose... 

The 2-C-methylene derivatives (17) are available by condensation of 1,1-di-methoxyprop-2-en-2-yl-lithium with 2,3-O-isopropylidene-D-glyceraldehyde, with the erythro-isomcx predominating over the t/zreo-isomer (7 3). Methanolysis of (17) afforded methyl 2-deoxy-2-C-methylene-j3-D-e/ yf ro-pentopyranoside and methyl 2-deoxy-2-C-methylene-0 -L-r)i/ eo-pentopyranoside from the erythro-... 

Using butyl glyojgrlate as the dienophile a new strategy to prepare 3-deoxy-D-manno-2-octulosonic acid (KDO), 2-deo) -KDO and thioglyco-side of KDO has even been proposed, starting from a diene derived from D-glyceraldehyde. ... 

The NR molecule is widely accepted to be synthesized by the successive addition of IPP to dimethylallyl diphosphate (DMAPP) to build up isoprene units in the cis configuration. Initial biochemical studies presumed that IPP, a precursor of rubber molecules from higher plants, is synthesized via the mevalonate (MVA) pathway,which is operated in the cytoplasm from acetyl-Co A. Later, a non-mevalonate pathway called the methylerythritol phosphate (MEP) pathway has also been considered as responsible for IPP synthesis in the plastids from the condensation of pyruvate and glyceraldehyde-3-phos-phate. Mevalonate and l-deoxy-o-xylulose-5-phosphate (DXP) are intermediates in MVA and MEP pathways, respectively. DMAPP is produced by the isomerization of IPP, catalysed by IPP isomerase, from both pathways. The gene expression of DXP synthase in Hevea latex suggested that the MEP pathway for IPP synthesis is involved in rubber biosynthesis.However, an experiment that involved feeding 600 RRIM seedlings with [l- C] 1-deoxy-o-xylulose triacetate, an intermediate derivative of the MEP pathway, indicated that the MEP pathway is involved only in carotenoid biosynthesis but not in the case of rubber biosynthesis. ... 

Chain extension. - Dondoni and co-workers have further exemplified the utility of thiazole chain-extension chemistry with the synthesis of 2-acetamido-2-deoxy-D-mannose (2) from the D-arabinose diacetonide 1 (Scheme 1), and the kanosamine derivative 4 from the D-eiythrose derivative 3 (Scheme 2), itself prepared fintxn 2,3-6>-is< )ropylidene-D-glyceraldehyde by a one carbon extension via diiazole anion addition. The methodology in Scheme 1, which features an improved thiazole to aldehyde deprotection sequence (step v), was also used to synthesize 2-amino-2-deoxy-D-mannose and, in adition, 2-amino-2-deoxy-D-erythrose from 2,3-0-isopropylidene-D-glyceraldehyde. 

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