Monosaccharides chirality

Synthesis of chiral monosaccharides. Masamune, Sharpless, and coworkers2 have developed a general, iterative sequence for addition of two chiral hydroxymethy-lene units to an aldose. The key step involves regio- and stereoselective ring opening... 

The diboronic acids 23 and 24 form rigid cyclic complexes with chiral monosaccharides and disaccharides this is the origin of the CD observations. The induced chirality upon formation of rigid, chiral complexes was monitored by CD spectroscopy, and this rigidification process can be utilized in the design of spectroscopic... 

Assign R or S configuration to each chirality center in the following monosaccharides, and tell whether each is a o sugar or an t. sugar ... 

Competitive binding studies have shown that 164 and 166 are suitable for the detection of glucose at physiological levels [253-255]. Diboronate 165 is capable of chiral recognition of monosaccharides and gave the best chiral recognition for fructose when tested with a series of different saccharides [255]. 

Aldonolactones are useful starting materials for the synthesis of modified sugars. They have also been used as chiral templates in synthesis of natural products. Some of them are inexpensive, commercially available products or they may be obtained readily from the respective monosaccharides. The purpose of this chapter is to survey the main reactions of aldonolactones. Previous reviews on the subject include articles on gulono-1,4-lactones (1) and D-ribonolactone (2). Methods of synthesis, conformational analysis, and biological properties are not discussed in this chapter. 

The introduction of g.l.c. for oligosaccharide analysis constituted a major breakthrough in the field. In addition to strategies for accurate and sensitive quantitation of monosaccharide type (19,20), chiral procedures may be adopted for enantiomeric (d and l) determination (21). The sensitivity of h.p.a.e. chromatography with pulsed amperometric detection now provides an alternative to g.l.c. for oligosaccharide compositional analysis (22). 

The monosaccharides have a couple of characteristics that prove to be important in terms of their structure and function. They all have at least one carbon that is bonded to four different groups (a chiral carbon), and most form five-and six-membered rings easily. The presence of chiral carbons allows these compounds to exist as two different optical isomers that are nonsuperimposable mirror images of each other. (Your feet are nonsuperimposable mirror images. Try putting a left shoe on a right foot )... 

Van Boom and co-workers published an expeditious route to chiral oxepines with monosaccharide derivatives as precursors. The synthesis was accomplished by treatment of 210 with alkoxyallenes 8 under Rutjes s optimized reaction conditions (Scheme 8.50) [121]. 

In 1966 Landor and co-workers reported the preparation of chiral derivatives of LAH by its reaction with monosaccharide derivatives (46,61). These studies have been reviewed by Inch (62). Landor and co-workers planned to construct... 

In connection with the synthetic work directed towards the total synthesis of polyene macrolide antibiotics -such as amphotericin B (i)- Sharpless and Masamune [1] on one hand, and Nicolaou and Uenishi on the other [2], have developed alternative methods for the enantioselective synthesis of 1,3-diols and, in general, 1, 3, 5...(2n + 1) polyols. One of these methods is based on the Sharpless asymmetric epoxidation of allylic alcohols [3] and regioselective reductive ring opening of epoxides by metal hydrides, such as Red-Al and DIBAL. The second method uses available monosaccharides from the "chiral pool" [4], such as D-glucose. 

As part of a strategy of employing monosaccharides as a convenient source of chirality, organometallic additions to protected L-erythrulose derivatives have been carried out. Employing silyl, benzyl, trityl, and acetonide protecting groups, the diastereoselectivities obtained are discussed in terms of chelation to the a-and/or the /3-oxygen, and are compared with results for similar aldehydes. 

Since monosaccharides containing six carbon atoms, such as D-glucose, have five chiral centers, we have a total of 2 = 32 possible hexoses. For the monosaccharides containing five carbon atoms, there are four chiral centers, for a total of... 

Monosaccharides generally have multiple chiral centers. 

The most important natural monosaccharide, D-glucose, is an aliphatic aldehyde with six C atoms, five of which carry a hydroxyl group (1). Since C atoms 2 to 5 represent chiral centers (see p. 8), there are 15 further isomeric aldohexoses in addition to D-glucose, although only a few of these are important in nature (see p.38). Most natural monosaccharides have the same configuration at C-5 as D-glyceraldehyde-they belong to the D series. 

Another route to a methyl-branched derivative makes use of reductive cleavage of spiro epoxides ( ). The realization of this process was tested in the monosaccharide series. Hittig olefination of was used to form the exocyclic methylene compound 48. This sugar contains an inherent allyl alcohol fragmenC the chiral C-4 alcohol function of which should be idealy suited to determine the chirality of the epoxide to be formed by the Sharpless method. With tert-butvl hydroperoxide, titanium tetraisopropoxide and (-)-tartrate (for a "like mode" process) no reaction occured. After a number of attempts, the Sharpless method was abandoned and extended back to the well-established m-chloroperoxybenzoic acid epoxida-tion. The (3 )-epoxide was obtained stereospecifically in excellent yield (83%rT and this could be readily reduced to give the D-ribo compound 50. The exclusive formation of 49 is unexpected and may be associated with a strong ster chemical induction by the chiral centers at C-1, C-4, and C-5. 

Rare or unnatural monosaccharides have many useful applications as nonnutritive sweeteners, glycosidase inhibitors and so on. For example, L-glucose and L-fructose are known to be low-calorie sweeteners. In addition, rare or unnatural monosaccharides are potentially useful as chiral building blocks for the synthesis of biologically active compounds. Therefore, these compounds have been important targets for the development of enzymatic synthesis based in the use of DHAP-dependent aldolases alone or in combination with isomerases. Fessner et al. showed that rare ketose-1-phosphates could be reached not only by aldol addition catalyzed by DHAP-dependent aldolases, but by enzymatic isomerization/ phosphorylation of aldoses [35]. Thus, for example, L-fructose can be prepared... 

The carbonyl group (and adjacent alcohol) oxidizes with excess phenyl hydrazine (PhNHNH2) to form an osazone (see Figure 16-15). Osazone formation is very important in determining the relationship between various monosaccharides. For example, both D-glucose and D-mannose produce the same osazone, so they re epimers. Epimers differ by only one chiral center, which osazone formation destroys. 

The nomenclature and classification of monosaccharides is further complicated by the presence of chiral carbons within monosaccharides. In the late nineteenth century it was ascertained that the configuration of the last chiral carbon in each of the naturally occurring monosaccharides is the same as that for (-i-)-glyceraldehyde. This configuration was designated as D and it was determined that all naturally occurring monosaccharides were in the D configuration. 

From among the variety of non-carbohydrate precursors, acetylenes and alkenes have found wide application as substrates for the synthesis of monosaccharides. Although introduction of more than three chiral centers having the desired, relative stereochemistry into acyclic compounds containing multiple bonds is usually difficult, the availability of such compounds, as well as the choice of methods accessible for their functionalization, make them convenient starting-substances for the synthesis. In this Section is given an outline of all of the synthetic methods that have been utilized for the conversion of acetylenic and olefinic precursors into carbohydrates. Only reactions leading from dialkenes to hexitols are omitted, as they have already been described in this Series.7... 

---