Benzyl derivatives hydrolysis

Porcine liver esterase (PLE) gives excellent enantioselectivity with both dimethyl 3-methylglutarate [19013-37-7] (lb) and malonate (2b) diester. It is apparent from Table 1 that the enzyme s selectivity strongly depends on the size of the alkyl group in the 2-position. The hydrolysis of ethyl derivative (2c) gives the S-enantiomer with 75% ee whereas the hydrolysis of heptyl derivative (2d) results in the R-monoester with 90% ee. Chymotrypsin [9004-07-3] (CT) does not discriminate glutarates that have small substituents in the 3-position well. However, when hydroxyl is replaced by the much bulkier benzyl derivative (Ic), enantioselectivity improves significantly. 

NBS, CH3CN, H2O, 62-90% yield.The POM group has been selectively removed in the presence of an ethoxy ethyl ether, TBDMS ether, benzyl ether, p-methoxybenzyl ether, an acetate, and an allyl ether. Because the hydrolysis of a pentenyl 2-acetoxyglycoside was so much slower than a pentenyl 2-benzyloxyglycoside, the 2-benzyl derivative could be cleaved selectively in the presence of the 2-acetoxy derivative. The POM group is stable to 75% AcOH, but is cleaved by 5% HCl. 

Benzyl carbamates substituted with one or more halogens are much more stable to acidic hydrolysis than are the unsubstituted benzyl carbamates.For example, the 2,4-dichlorobenzyl carbamate is 80 times more stable to acid than is the simple benzyl derivative. Halobenzyl carbamates can also be cleaved by hydrogenolysis with Pd-C. The following halobeni yl carbamates have been found to be useful when increased acid stability is required. 

Phosphinamides are stable to catalytic hydrogenation, used to cleave benzyl-derived protective groups, and to hydrazine. The rate of hydrolysis of phosphin-... 

Phosphinamides are stable to catalytic hydrogenation, used to cleave benzyl-derived protective groups, and to hydrazine. The rate of hydrolysis of phosphinamides is a function of the steric and electronic factors around the phosphorus. This derivative has largely been used for the protection of amino acids and occurs few, if any, times in the general synthetic literature. 

N-Hydroxy-N-nitrosamines with an aliphatic group at O2 produce a compound stable to aqueous acid and base (Fig. 3.4, 29) [158], whereas all other N-hydroxy-N-nitrosamines are susceptible to hydrolysis and appropriate 02-derivatives also render these materials vulnerable. The hydrolysis endpoint is the formation of nitroxyl (HNO) [which dimerizes to form nitrous oxide (N20)] and a C-nitroso compound. These products are formed from aryl [159] and alkyl bound unsubstituted diazenium-diolates as well as Oralkylated derivatives [160]. Studies of the solvolysis of Oi-alkyl derivatives are complicated by their tendency to decompose via competing radical pathways [161], but the Oi-benzyl derivatives are unique in that they hydrolyze back to the original synthetic precursors (Scheme 3.14) [162]. 

The methyl and benzyl derivatives (289 R = Me, PhCH2 R = H) were described by Claus and Howitz in 1891. Their preparation involves N-alkylation of 6-hydroxyquinoline and base hydrolysis to the quaternary hydroxide which is then desiccated, giving the hygroscopic betaines 289. ° The 2-phenyl derivative (289 R = Me, R = Ph) has been similarly prepared. With methyl iodide, the phenol betaine (289 R = Me, R = H) gives Af-methyl-6-methoxyquinolinium iodide. ... 

O-Benzylation of 148 with benzyl bromide in the usual manner yielded the tri-0-benzyl derivative (149), [a]p7 —0.8° (chloroform). On hydrolysis with aqueous acetic acid, 149 gave the compound (150), which was further converted to the compound (151) by sodium borohydride reduction. Periodic acid oxidation of 151 and successive sodium borohydride reduction gave 5,6-di-<9-acetyl-2,3,4-tri-0-benzyl-pseudo-a-L-altropyranose (152), [a] 6 —25.7° (chloroform), after conventional acetylation. Reductive cleavage of 152 with sodium in liquid ammonia and subsequent acetylation afforded pseudo-a-L-altropyranose pentaacetate (153), m.p. 84-85 °C, [ ]q6 —13.7° (chloroform). Hydrolysis of 153 gave 154, [ot] —43.6° (methanol) [35] (Scheme 24). 

Japanese chemists (96) have reported the chemical conversion of kobusine into the chloramine (95). The latter was treated with sodium methoxide in methanol to afford compound 96 in which the bridged C-14-C-20 bond was cleaved. Reduction of kobusine with sodium in n-propanol, followed by acetylation afforded compound 88. Treatment of 88 with excess phenyl chloroformate in refluxing o-dichlorobenzene gave the carbamate 89. The latter was hydrogenated over Pd-C in methanol to obtain compound 90 in 94% yield. Further hydrogenation of 90 in the presence of platinum in acidic solution gave 91. Acidic hydrolysis of 91 afforded compound 92. The carbamate 92 was converted to the benzyl derivative 93 by treating with... 

Brossi and Wenis have prepared halfordinol (16) by cyclodehydration of the a-amido ketone 60 followed by hydrolysis of the intermediate O-benzyl derivative 61 (24). 

Acetamido-5-deoxy-D-ribose has been synthesized from benzyl 2,3-O-isopropylidene-)3-0-ribofuranoside through the sequence of the 5-0-p-tolylsulfonyl, 5-azido, and 5-acetamido derivatives. Hydrolysis of benzyl 5-acetamido-5-deoxy-2,3-0-isopropylidene-j8-D-... 

---