Carbon aldoses

Deoxy-3-[(l/Z,2S)-l,2-dihydroxy-3-oxopropyl]-D-gZycer0-D-aZfr0-heptopyranose or 3-deoxy-3-(D-f/jreo-1,2-dihydroxy-3-oxopropyl)-D-g/ycero-D-a/rro-heptopyranose (not the alternative open-chain six-carbon dialdose or eight-carbon aldose, cf. 2)... 

In 1991, Whitesides etal. reported the first application of aqueous medium Barbier-Grignard reaction to carbohydrate synthesis through the use of tin in an aqueous/organic solvent mixture (Eq. 8.48).106 These adducts were converted to higher carbon aldoses by ozonolysis of the deprotected polyols followed by suitable derivatization. The reaction showed a higher diastereoselectivity when there was a hydroxyl group present at C-2. However, no reaction was observed under the reaction conditions when there was an /V-acctyl group present at the C-2 position. 

Supplementary synthetic methods for preparing higher-carbon aldose and ketose sugars from the more accessible lower-carbon sugars are obviously desirable. The present review describes the recent development of two such methods based on the application to sugar... 

It will be noted that not only are higher-carbon aldose sugars and ketose sugars available through the nitromethane and 2-nitroethanol... 

Since his proof depended in part on the relationship between (+) glucose and the aldopentose (—)-arabinose, Fischer also had to consider the configurations of the five-carbon aldoses. Of the eight possible configurations, he. retained only four, IX Xn, again those in which the bottom chiral center carried the —OH on the right. 

The sodium deoxynitroalditols are readily decomposed with dilute sulfuric acid to give the corresponding higher-carbon aldose sugars, which... 

The simplest carbohydrate is the aldotriose, glyceraldehyde (Fig. 3-1). The 4-carbon aldoses are related to D- and L-glyceraldehyde and can be viewed as having been stracturaUy derived from them by the introduction of a hydroxylated chiral carbon atom between C-1 and C-2. Thus there are four aldotetroses. Two simple aldopentoses can be derived stmcturally from each of the fom aldotetroses described, making a total of eight aldopentoses. 

The search for oil-independent and renewable alternatives for the production of chemicals, fuels, and materials has led to an increased interest in the use of biomass as a feedstock [1, 2]. The catalytic conversion of biomass, and in particular that of the most abundant and non-edible lignocellulosic feedstock, has led to new pathways for the synthesis of chemicals, biofuels, and polymer building blocks [3-17]. Cellulose is the single most abundant organic compound on Earth [8,18]. As this biopolymer exclusively consists of glucose, a 6-carbon aldose, as seen in Fig. 1, its selective conversion to desired chemical compounds is feasible [8, 9, 19]. 

Glycoses are classified by the total number of carbon atoms. The glycose with three carbon atoms (2, n = 1) is called a triose, and when there are four carbon atoms (2, n = 2), it is a tetrose. A pentose has five carbon atoms (2, n = 3) and a hexose has six carbon atoms (2, n = 4). If the carbonyl unit in 2 is an aldehyde, it is an aldose (see preceding discussion) thus, a three-carbon aldose is an aldotriose and a six-carbon aldose is an aldohexose. If the carbonyl unit in 2 is a ketone unit, the molecule is a ketotetrose, a ketohexose, etc. 

This oxidative cleavage reaction is a good synthesis of smaller carbon aldoses from larger carbohydrates (a chain-shortening reaction). 

The nitromethane synthesis of higher-carbon aldose sugars utilizes two well-known general reactions of the nitroparaflBns. These are the base-catalyzed condensation of nitromethane with an aldehyde to produce a C-ni-troalcohol (146), and the decomposition of the sodium salt of the latter with cold, moderately concentrated mineral acid to produce an aldehyde (147) containing one more carbon atom than the original aldehyde. 

In addition to the saturated disulfone (II), unsaturated (III) and anhy-dro (IV) disulfones have been identified as products of the oxidation with certain of the mercaptals 200, 201). Both of the latter modifications of the disulfone, however, also degrade smoothly to the lower-carbon aldose. 

Aldopentoses are five-carbon aldoses. These carbohydrates contain three stereogenic carbons, and so there must be a total of eight stereoisomers (2 = 8). Figure 22.7 shows the four members of the D series of aldopentoses and their common names. 

Aldohexoses are six-carbon aldoses. They have four stereogenic carbons and so there must be a total of 2 = 16 stereoisomers, eight in the D series (Fig. 22.8) plus... 

D-Erythrose is a four-carbon aldose. Addition of a formyl substituent to Cl leaves C2, C3, and C4 unchanged, while changing the original carbonyl group to that of a secondary alcohol. The emerging new stereocenter may form with either the Rot S configuration. 

---