Glyceraldehyde acidic conditions

The isolation of pyruvaldehyde enol ethers rather than glyceraldehyde structures during mild acidic hydrolysis may indicate that the latter structures are not stable in their free form but tend to lose water to produce pyruvaldehyde enol ether structures. Such structures may therefore be formed in lignin during technical processes carried out under mild acidic conditions such as the production of TMP. Pyruvaldehyde enol ether structures absorb UV-light above 300 nm and may thus contribute to the photo-yellowing process. Under conditions simulating the production of CTMP, on the other hand, it was previously shown that these types of structures are rapidly and completely eliminated presumably by sulfonation reactions (75). 

The nitroaldol condensation with nitromethane (Henry s reaction), followed by Nef decomposition of the resultant nitronate under strongly acidic conditions, has been used to elongate aldehydes. For instance, A-acetyl-D-mannosamine has been converted into A-acetylneuraminic acid applying this method iteratively [69]. Chikashita and coworkers [70] have reported good levels of anti diastereoselectivity better than 99% in an iterative homologation sequence using 2-lithio-l,3-dithiane [71] with 2,3-O-cyclohexylidene-D-glyceraldehyde R)-62. In the case of the BOM-protected tetrose derivative, the addition of 2-lithio-l,3-dithiane was syn selective (synlanti 82 18) (Scheme 13.30). 

Alcohol 143 (Scheme 6.26), prepared from (R)-glyceraldehyde derivative, was subjected to deoxygenation and epoxidation to give the racemic epoxide 144. Kinetic resolution with (S,S)-Jacobsen catalyst gave diol 145, which on further transformations was converted into the alcohol 146. Swern oxidation of 146 followed by Wittig olefination, acetonide deprotection under acidic conditions furnished the diol 147. Primary alcohol on deoxygenation through LAH reduction of tosylate afforded the alcohol 148. 

The reaction protocol was further extended to the concise synthesis of poly-oxamic acid, the unique polyhydroxyamino acid side-chain moiety of the antifungal polyoxin antibiotics (63). Treatment of the template 205 under standard thermal cycloaddition conditions with (5)-glyceraldehyde acetonide led to the formation of a single diastereoisomer 208 in 53% yield. Subsequent template removal released polyoxamic acid 209 in essentially quantitative yield. This represents a matched system, with the mismatched system leading to more complex reaction mixtures (Scheme 3.70). 

These adverse conditions have elicited considerable efforts to reduce the number of chiral centers as well as hydroxyl groups with the simultaneous introduction of useful functional groups (10, 13-15). One approach involves the shortening of the aldose carbon chain, or, more simply, its bisection, as exemplified by the use of D-mannitol-derived 2,3-Oisopropylidene-D-glyceraldehyde. Whilst this product and its L-ascorbic acid-derived enantiomer have developed into popular enantiopure three-carbon synthons (16), it may be objected that the photosynthetic achievement of Nature which graciously provides us with six-carbon compounds, is utilized rather inefficiently, clearly pointing towards elaboration of synthons from sugars with retention of the carbon chain. 

The common nonenolide core of ascidiatrienolide and the didemnilactones has been formed as shown in Scheme 5 (22). Specifically, a tin-mediated, ultrasound-promoted addition of allyl bromide to unprotected glyceraldehyde 37 furnished a mixture of the corresponding homoallyl alcohols 38 which were subjected to acetalization and esterification with 5-hexenoic acid under standard conditions. At that stage, the major jy/i-isomer 40 can be purified by flash chromatography. Exposure of this diene to a refluxing solution of the ruthenium... 

Acetals are readily hydrolyzed by dilute mineral acids however, the yields are not always satisfactory. These substances are not affected by alkaline reagents. The sensitive JZ-glyceraldehyde acetal is converted to its aldehyde in 80% yield by the action of dilute sulfuric acid under mild conditions. Other procedures are illustrated by the treatment of acetals which are formed by the interaction of Grignard reagents and orthoformic esters (method 165). 

The pentose phosphate pathway produces NADPH for fatty acid synthesis. Under these conditions, the fructose 6-phosphate and glyceraldehyde 3-phosphate generated in the pathway reenter glycolysis. 

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