Debenzoylation

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. 

The bromide (2a) reacted also with chloromercuri-N-benzoyladenine to give, after debenzoylation, 9- (2-deoxy-/ -D-arabino-hexopyranosyl) -adenine (15). A later paper reported (18) on the coupling of 2a with... 

Carbanions of active methylene compounds also react with aziridine-2-car-boxylic esters to give ring-opened products [129]. The ring-opened intermediates usually cyclize spontaneously to pyrrolidones. Treatment of 190 (Scheme 3.70) with the sodium enolate of dimethyl malonate 191, for example, afforded pyrroli-done 192 in 15% isolated yield, together with 30% of the debenzoylated product 193. 

Ethyl 3-benzoyl-2-quinoxalinecarboxylate 1,4-dioxide (5) gave 2-quinoxaline-carboxylic acid 1,4-dioxide (6) (KOH, EtOH, 20°C, rapidly 58% note additional debenzoylation). " ... 

Benzoyl-l-benzyloxycarbonylmethyl-3,4-dihydro-2(17i)-quinoxalinone (14) gave l-carboxymethyl-3,4-dihydro-2(l//)-quinoxalinone (15) (Pd/C, AcOEt, H2, 20°C, 90% note additional A-debenzoylation)." ... 

A very attractive and efficient method for the synthesis of L-aminoacids via DKR has been reported by Turner et al. [41a,b]. They employed enzyme-catalyzed ring opening of 5(4H)-oxazolones in combination with a catalytic amount of Et3N. The relatively low pKa of the C-4 proton (8.9) of oxazolones facilitates racemization. Hydrolysis of the ester obtained through DKR, followed by debenzoylation, yields L-aminoacids in excellent enantiomeric excess (99.5%) (Figure 4.16). In their initial studies, they employed Rhizomucor miehei lipase (Lipozyme) as the biocatalyst [41]. More recently, they have obtained excellent results employing CALB [41bj. This method has also been employed by Bevinakatti [41c,d] and Sih [41e,fj. 

R,3S)-N-debenzoyl-N-tert-butoxycarbonyl-10-deacetyl-2-(1 -ethoxyethyl)-7,10-bis-(triethylsilyl)taxol (XXIII)... 

En route to the total synthesis oftashironin (7-114a) and the debenzoylated compound 7-114b, which shows an interesting promotion of neurite growth, Danishefsky and coworkers have developed a domino oxidative dearomatization/trans-annular Diels-Alder reaction [54]. In this line, treatment of 7-115 with phenyl-iodine(III) diacetate (PIDA) led to an intermediate 7-116, which immediately underwent a transannular Diels-Alder reaction to furnish the complex cycloadducts 7-117 in good yields (Scheme 7.31). 

Compound 35 has also been obtained51 from 32, by sequential debenzoylation, and acetalization with 2,2-dimethoxypropane. It has been used in the synthesis, in good overall yield, of versatile, ano-merically functionalized precursors of C-nucleosides having the d-arabino or the D-ribo configuration. 

Anhydro-D-mannitol is also obtained by a novel route from 1,6-dibenzoyl-D-mannitol. When this compound is heated with p-tolu-enesulfonic acid in acetylene tetrachloride, it suffers partial dehydration and one of the products is a dibenzoyl derivative of mannitan. On debenzoylation of this substance it yields crystalline 1,4-anhydro-D-mannitol.67 The formation of dibenzoyl-1,4-anhydro-D-mannitol has involved the migration of at least one benzoyl group and Hockett and coworkers6 believe that the initial product is either 2,6- or 3,6-dibenzoyl-1,4-anhydro-D-mannitol. 

When the benzoylated lactone 172a was debenzoylated with sodium methoxide and the product boiled in 1,4-dioxane, the more-stable 1,4-lactone 175 was isolated upon rebenzoylation. Reduction of the lactone carbonyl group afforded (220) the crystalline furanose derivative (176) of ascarylose. A similar procedure, performed on the benzoylated 3-deoxy-D-arabino-hexono-1,5-lactone 170, gave (221) the 3-deoxy-D-oraWno-hexo-furanose derivative. 

The 7-(2-hydroxyethyl)guanine derivative 1139 was obtained in two steps from guanosine (1138) (61JCS3923). Benzoylation of 1139 followed by thiation gave 1140, which upon debenzoylation gave 1141, whose dethiation was affected to give 1142 (89MI8). 

The synthesis of four out of eight possible stereoisomers of 3-methyllanthionine [(25,35,67 ), (25,37 ,67 ), (25,35,65), (25,37 ,65)] has been achieved using the reaction of Z-protected 3-methyl-D-cysteine with d- or L-3-chloroalanine in yields of 35—53% J64 The methyl-D-cys-teine stereoisomers were obtained by two routes. Firstly from (25,35)-threonine via O-tosylation and subsequent inversion of configuration by nucleophilic attack with thiobenzoic acid. The resulting derivative was debenzoylated and oxidized to the respective cystine derivative prior to the reduction with Zn/HCl to give the eryt/u-o-3-methyl-D-cysteine... 

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. 

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