Sugar, synthetic substitutes

Sweetness is a gustatory response evoked by most sugars, and is relished by man as well as by many other organisms. The desire for sweetness appears to be universal and undisputed. Today, sugar, or one of its synthetic substitutes, appears in more articles of the diet than any other food ingredient, except, perhaps, common table salt. ... 

There is no evidence to indicate that such acetyl groups are added to neutral sugars or uronic acids before polymer assembly. The sugar nucleotide donors, such as UDPXyl, are all derivatives of simple sugars synthetic nucleotides based upon substituted sugars have generally been found to be totally inactive. Hence acetyl transfer probably occurs after glycosyl transfer, but quite possibly before the polymer is complete. How many acetyltransferases exist is unknown. 

Vinyl epoxides are highly useful synthetic intermediates. The epoxidation of dienes using Mn-salen type catalysts typically occurs at the civ-olefin. Epoxidations of dienes with sugar-derived dioxiranes have previously been reported to react at the trans-olefin of a diene. A new oxazolidinone-sugar dioxirane, 9, has been shown to epoxidize the civ-olefin of a diene <06AG(I)4475>. A variety of substitution on the diene is tolerated in the epoxidation, including aryl, alkyl and even an additional olefin. All of these substitutions provided moderate yields of the mono-epoxide with good enantioselectivity. 

The direct attachment of adequately substituted mexo-arylporphyrin to the saccharide units has been another synthetic strategy. Mexo-tetraaryl-porphyrins were used as templates to append, directly or by a spacer, several sugar units at the ortho, meta or para positions of the phenyl ring (Fig. 1). 

In related work, Rutjes and co-workers reported a four-step protocol from conveniently protected sugar derivatives to substituted C-l glycals (Scheme 16).77 The key step in their synthetic route included RCM of highly functionalized a-alkoxyacrylates. The potential of these glycal derivatives was illustrated by their conversion to natural products such as DAH (3-deoxy-D-arabino-2-heptulosonic acid) or KDO (3-deoxy-D-manno-2-ulosonic acid). 

Chi is purified from chloroplast extracts, usually obtained from spinach leaves, by dioxane precipitation method (51) and conventional sugar column chromatography (52). For rapid and easy preparation, the method recently developed by Omata and Murata (53) is satisfactory synthetic (DEAE-) Sepharose is substituted for sugar on the column. Besides using spectroscopic criteria (52), the purity of Chi samples can be checked readily by means of silica-gel thin layer chromatography (54). Colorless contaminations in Chi... 

Peripheral functionalization (2, 7,12, and 17 positions) of porphycenes has relied on the use of ( > - m e th o x ye thy I - s u b s t i t u ted porphycenes. Synthetic sequences such as removal of a methyl ether group of 3-methoxyethyl-substituted porphycene 48 (M=H2) (Scheme 24) with a Lewis acid such as BBr3 produces the alcohol 49 or other substituted products 50 (R=Br) (1994JMC2797). The hydroxyl-substituted porphycene 49 has further been converted to porphycene sugar derivatives (19730R455). Further, both bromide 50 (R=Br) and mesylate 50 (R=OMs) produced from hydroxyl derivative 49 undergo substitution with NaCN to afford the cyano derivative 50 (R=CN), and then converted to a carboxylic ester 50 (R=COOEt) and its saponified product 50 (R=COOH) (1993MI). 

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