Debenzoylation selective

Benzoates. The selective debenzoylation of sucrose octabenzoate [2425-84-5] using isopropylamine in the absence of solvents caused deacylation in the furanose ring to give 2,3,4,6,1/3/6 -hepta- and 2,3,4,6,1/6 -hexa-O-benzoyl-sucroses in 24.1 and 25.4% after 21 and 80 hours, respectively (54). The unambiguous assignment of partially benzoylated sucrose derivatives was accompHshed by specific isotopic labeling techniques (54). Identification of any benzoylated sucrose derivative can thus be achieved by comparison of its C-nmr carbonyl carbon resonances with those of the assigned octabenzoate derivative after benzoylation with 10 atom % benzoyl—carbonyl chloride in pyridine. 

In connection with the synthesis of C-glycosyl compounds, Moffatt and coworkers182 developed the selective debenzoylation of 2,3,5-tri-0-benzoyl-/3-D-ribofuranosyl cyanide, which had been reported earlier163 reaction in methanolic ammonia-chloroform at 0° gave the crystalline 5 -0-benzoyl derivative in 83% yield, without recourse to chromatography. 

Selective debenzoylation has been shown to occur by Restelli de Labriola and Deulofeu160 in the cleavage of penta-O-benzoylhexonic acid nitriles (LXXXIII) to form O-benzoyl-pentose dibenzamides (LXXXIV) with ammonia. Since tetra-O-benzoyl-L-rhamnonic acid nitrile (LXXXV) yields 5-deoxy-L-arabinose dibenzamide (LXXXVI), the benzoyl group in the Wohl degradation products is assumed to be in the 5 positions of the resulting pentoses. 

As early as 1994, Chaudhary et al. enabled the facile SAR exploration at C-2, which is possible by establishment of the selective C-2 debenzoylation method... 

Datta, A. Jayasinghe, L. R. Georg, G. I. Intenal nucleophile assisted selective deesterification studies on baccatin HI. Synthesis of 2-debenzoyl and 4-deacetylbaccatin III analogues. J. Org. Chem., 1994, 59 4689-4690. 

One such example, depicted in Scheme 8.17, incorporates the classical dithioacetal opening of D-glucose. As illustrated, selective benzoylation of the primary hydroxyl, followed by di-acetalization and debenzoylation, afforded alcohol 56. The primary alcohol in 56 was displaced... 

The reaction of 148 with 10% HCl-MeOH afforded selective hydrolysis of the amide to form the 3-aminopyridine 149, in which the ring was subsequently closed after treatment with palladium(O) to give the /3-carboline 150. Friedlander condensation of 150 with 2-amino-3-benzyloxy-4-bromo-benzaldehyde (151), which was synthesized in four steps (5S), gave the 2-/3-carbolinequinoline 152. Hydrogen bromide gas debenzoylation of 152 was followed by oxidation with potassium nitrosodisulfonate (Fremy s salt) to obtain Kende s intermediate 131. 

The first requirement for the synthesis of analogs at C-2 is the development of methods for the selective removal of the C-2 benzoyl group, and several methods to do this have been developed, both in the baccatin series and in the taxol series. Thus treatment of 7,13-di(triethylsilyl)baccatin HI with Red-Al or with t-BuOK gave the 2-debenzoyl derivative 3.4.1 104, 105). Selective hydrolysis of 13-oxo-7-triethylsilyl-lO-deacetylbaccatin 3.4.2 to its 2-debenzoyl derivative 3.4.3 could be achieved by treatment with K2CO3 in methanol 106), and selective debenzoylation of 7,10-di-(triethylsilyl)-13-trimethylsilyl-10-deacetylbaccatin III with Red-Al to give 3.4.4 has also been carried out 107, 108). 

Direct debenzoylation of taxol has also been achieved, in spite of the fact that the side chain is hydrolyzed readily. The key to selectivity is to protect the 2 -hydroxyl group with a bulky and base-stable protecting group the t-butyldimethylsilyl group is ideal, but the triethylsilyl group also works. With both the C-7 and C-2 hydroxyl groups protected, hydrolysis of taxol can be accomplished in reasonable yield by treatment... 

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