Benzyloxycarbonyl group hydrogenolysis

A -Benzyloxycarbonyl groups, catalytic hydrogenolysis in sulfur-containing peptides, 59, 166... 

Treatment of 25 and 26, respectively, in pyridine with equimolar amounts of benzyloxycarbonyl chloride at low temperature, followed by addition of an excess of ethoxycarbonyl chloride, yielded the corresponding methyl 5-0-(benzyloxycarbonyl)-2-0-(ethoxycarbonyl)-/3-(57) and -a-D-glucofuranosidurono-6,3-lactone (58). Hydrogenolysis of the benzyloxycarbonyl group resulted in formation of methyl 2-0-(ethoxycarbonyl)-/ - (59) (70%) and -a-D-glucofuranosidurono-6,3-lactone (60) (30%), respectively, both in crystalline form. The /3-D... 

AM Felix, MH Jimenez, T Mowles, J Meienhofer. Catalytic hydrogenolysis in liquid ammonia. Cleavage of V -benzyloxycarbonyl groups from cysteine-containing peptides with terf-butyl side chain protection. Int J Pept Prot Res 11, 329, 1978. 

K Kuromizu, J Meienhofer. Removal of the JW-benzyloxycarbonyl group from cysteine-containing peptides by catalytic hydrogenolysis in liquid ammonia, exemplified by a synthesis of oxytocin. J Am Chem Soc 96, 4978, 1974. 

The racemic mixture of Z-Gly-DL-Alap can be separated to give pure enantiomers by simple crystallization with enantiomeric a-methylbenzylaminesJ7] An example of the separation of enantiomers is given in Scheme 5 for the separation of Z-L-Ala-D-Ala and Z-L-Ala-D-Ala.[7] The N-terminal protecting benzyloxycarbonyl group is removed by standard hydrogenolysis on 5% Pd/C catalyst. 

An illustrative example of the introduction of the benzyloxycarbonyl group, and its removal by hydrogenolysis is given in the synthesis of L-prolylglycine (Expt 5.188). An alternative reagent for the removal of this protecting group is iodotrimethylsilane in acetonitrile at room temperature.229... 

The benzyloxycarbonyl group is added by using an acyl chloride and can be removed by hydrogenolysis ... 

The final step in the solution-phase synthesis is to deprotect the N terminus of the completed peptide. The N-terminal amide bond must be cleaved without breaking any of the peptide bonds in the product. Fortunately, the benzyloxycarbonyl group is partly an amide and partly a benzyl ester, and hydrogenolysis of the benzyl ester takes place under mild conditions that do not cleave the peptide bonds. This mild cleavage is the reason for using the benzyloxycarbonyl group (as opposed to some other acyl group) to protect the N terminus. 

Solutions of free 6-amino-5-deoxy-D-xylose may also be obtained by catalytic hydrogenolysis of the benzyloxycarbonyl group from ihe pyranoid derivative (31), and by the reduction of 5-azido-5-... 

THF-Et O to give the potassium salt 163 of penam carboxylic acid (Scheme 30) (87NKK1447). Hydrogenolysis of the benzyloxycarbonyl group of 160b gave penam carboxylic acid 164 in 82% yield (87NKK1447). 

The benzyloxycarbonyl group (Cbz or Z) is useful in carbohydrate syuithesis, not only for IV-protection of amino sugars, but also to protect alcohols [262,263]. The main advantage of this group is that it is cleaved by hydrogenolysis, and when compared to benzyl ethers, benzyl carbonates are not only removed more readily [264] but also allow hydroxyl group protection under softer conditions than those employed for benzylation. 

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