Maltoside -, synthesis

Skrydstrup, Beau and co-workers122 have adapted Stork s method to the SmI2-reduction of glycosyl pyridyl sulfones bearing a silicon-tethered unsaturated group at HO-C(2). An example is shown with the synthesis of methyl a-C-zso-maltoside 172 from alkyne 170 via the 5-exo-dig radical cyclization of 171 (Scheme 56).144... 

SCHEME 9. Durette, Hough, and Richardson s synthesis of methyl 3-bromo-3-deoxy-p-maltoside via opening of the 2,3-allo-epoxide derived from the l,2,2, 3, 4, 6,6 -heptaacetate of methyl p-maltopyranoside (1974). 

Richardson and Hough s efforts on the chlorination of sucrose ran in parallel with their studies on the selective chlorination of other readily available disaccharides. One notable piece of work done with Philippe L. Durette involved a study of the regioselective chlorination of methyl (S-maltoside (Scheme 31), which was undertaken with the long-term objective of possibly developing a future synthesis of the natural antitumor agent, amicetin. 

In 2002, Do et al. [85] proposed a pathway for the enzymatic synthesis of (-)-menthyl a-maltoside and a-maltooligosides from (-)-menthyl a-glucoside using cyclodextrin glucanotransferase obtained from Bacillus macerans. The reaction can be performed in a reactor containing (-)-menthyl a-glucoside, the enzyme and soluble starch the yield was about 80% 15% (-)-menthyl a-malto-side and 65% (-)-menthyl a-maltooligosides, respectively. Treatment of the starch with a-amylase can raise the proportion of (-)-menthyl a-maltoside. 

Synthesis of methyl 3,6 3, 6 -dianhydro-/3-maltoside has been achieved by alkaline alcoholysis of the 6,6 -di-0-(methylsulfonyl) or 6,6 -di-0-p-tolylsulfonyl derivative of methyl /3-maltoside.20,23 Similar treatment of methyl 2,3,2, 3, 4 -penta-0-acetyl-6-deoxy-6 -0-p-tolyl-sulfonyl-/3-maltoside with ethanolic sodium hydroxide for 3.5 h at 60° afforded methyl 3, 6 -anhydro-6-deoxy-/3-maltoside in 90% yield.90... 

Ethyl l-thio-/3-maltoside heptaaeetate (59) has proved to be a useful intermediate in the synthesis of the a-glycoside of maltose (see Section III).30 Treatment of /3-maltose octaacetate with ethanethiol and fused zinc chloride gave compound 59 in 83% yield. Synthesis of mal-... 

In this case the predominance of glycosylation of C4-carbinols over substrate hydrolysis is in a mixture where the molar concentration of water was more than 3000 times that of the a-maltosyl fluoride. In other experiments the substrate concentration could be further reduced at least 5-fold without altering the fact of a substantially greater extent of maltosidic linkage synthesis than hydrolysis. We now are referring to a very dilute 4 mM, solution of substrate with which, if the hydrolase concept were valid, hydrolysis ought to have been predominant. 

D. Abbott and H. Weigel, Studies on dextrans and dextranases. Part V. Synthesis of the three carboxylic acids derived from methyl /1-maltoside, J. Chem. Soc., (1965) 5157-5162. 

Scheme 13. Synthesis of methyl a-C-maltoside 76 via temporary silaketal tethering...

Ferrer, M., Cruces, M. A., Plou, F. J. et al. (2000) A simple procedure for the regioselec-tive synthesis of fatty acid esters of maltose, leucrose, maltotriose and n-dodecyl maltosides. Tetrahedron, 56, 4053-4061. 

In general, the de novo approach applied by the Kishi group for the synthesis of C-oligosaccharides relies on acyclic stereocontrol for the construction of the contiguous chiral centers of at least one of the carbohydrate moieties. The first examples of this approach were reported by this group in 1987 and involved the synthesis of four C-disaccharides, including the C-analogs of methyl maltoside and cellobio-side, from a common synthetic intermediate [70]. 

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