Acetobromoglucose

A similar approach was used to prepare the octaglucosylated porphyrin derivative 34a obtained quantitatively after treatment of 34b with sodium methoxide and dry methanol (Fig. 3). The aldehyde used in the preparation of octaglucosylated derivative 34b was obtained in 90% yield by condensation of 3,5-dihydroxybenzaldehyde with acetobromoglucose 30 in the presence of Ag20.22 The condensation of pyrrole and the 2,5-bis(tetra-acetylglucopyranosyloxy)benzaldehyde occurred under Lindsey conditions and yielded porphyrinylsugar derivative 34b in 32%.22... 

Acetobromoglucose.—Glacial acetic acid is saturated at 0° with hydrogen bromide2 and 50 g. of the solution are poured on to 25 g. 

D-glucopyranosyl esters of abscisic acid and /3-ionylideneacetic acid (120) have been prepared by treatment of the acid with a-acetobromoglucose in the presence of triethylamine/ Two papers " describe a new synthesis of y-ionone (64) in which the key intermediate (121) is prepared from y-cyclocitral (122) and acetone in the presence of BU2BSO3CH2CF3. 

The first generation of an O-unprotected glycosyl donor that could be activated based on the remote activation concept was exemplified by 2-pyridylthio p-D-glucopyranoside 1 [10], which could be easily prepared from acetobromoglucose [11]. Treatment of 1 with a variety of alcohols in the presence of mercuric nitrate in acetonitrile solution led, within a few minutes, to the corresponding O-glycosides, with isolated yields and a/p ratios varying from methanol (70 30, 95%), to 2-propanol (62 38 77%), and cyclohexanol (51 49, 75%) Scheme 2. Identical results were obtained when 2-pyrimidinylthio p-D-... 

When acetobromoglucose was dissolved in ether, and treated with an aqueous, alkaline solution of benzenethiol, phenyl 1-thioglucoside was obtained acetobromolactose was also utilized successfully in this type of synthesis. 

When acetobromoglucose was treated with moist silver oxide, a mixture of bromine-free acetates was formed from which was obtained, besides glucose tetraacetate, a small proportion of a crystalline disaccharide octa-... 

Fischer s statement, cited above, that aspartic acid bears a simple relationship to the a-hydroxy acids and, consequently, to the sugars, was made with the explicit reservation that no Walden inversion may occur on deamination with nitrous acid (1896). This condition could not be retained. Furthermore, his conclusion that acetobromoglucose belongs to the /3-d series because it forms /3-D-glucosides is also inadmissible. It is amazing that these two cases seem to be the only ones in which he was misled by the then partially unknown, sometimes unfathomable phenomena of inversion. 

Glycosidation.4 p-D-Glucosides are obtained stereospecifically by reaction of acetobromoglucose with a protected sugar in CH2C12 in the presence of Sn(OTf)2 (1 equiv.) and a base (1 equiv. of collidine, diisopropylethylamine, or 1,1,3,3-tetramethylurea). Addition of 4 A molecular sieves ensures anhydrous conditions. Yields are 30-60%. 

The reactions involved in the glycal synthesis have been studied in considerable detail, especially in the conversion of arabinose into 2-des-oxyribose. For this particular conversion the overall yield has been doubled by recently introduced improvements but it is still very low.112 The reduction of the acetobromoaldose to the acetylated glycal by zinc dust and acetic acid was found to proceed in better yield if a few drops of chloroplatinic acid were added at intervals to maintain a vigorous reaction.112 120 127 Moreover, the reaction could then be conducted at lower temperatures (i. e., — 5° to —10°). This was particularly the case in the pentose series, and the simultaneous formation of the pentose tetraacetate by replacement of the bromo group by an acetyl residue, was much reduced.60 112 Hughes148 demonstrated that the maximum yield of triacetylglucal from acetobromoglucose was obtained when the addition of zinc dust and catalytic amounts of chloroplatinic acid was spread over several hours and the reaction mixture was maintained at 0°. 

Experiment 5.109 2.3.4.6-TETRA-O-ACETYL-oc-d-GLUCOPYRANOSYL BROMIDE (a-Acetobromoglucose)... 

E. Fischer and K. Zach, Reduction of acetobromoglucose, Sitzber. kgl. preuss. Akad. Wiss., 16 (1913) 311-317. 

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