Benzyloxycarbonyl group removal

The conversion of 3 to 8 is summarized in Scheme 2. The trityl group (too large and too acid sensitive for the ensuing steps) was removed from N, and both N s were protected by Cbz (benzyloxycarbonyl) groups. Protection of the tertiary OH specifically as the robust TBS (f-butyldimethylsilyl) group was found to be necessary for the sequence involving the electrophilic aromatic substitution step, 5 to 6, and the Stille coupling steps (6 + 7 —> 8). 

Removal of N -Benzyloxycarbonyl Groups from Sulfur-Containing Peptides BY Catalytic Hydrogenation in Liquid Ammonia O-tert-BurvL-L-SERYL-S-... 

REMOVAL OF N -BENZYLOXYCARBONYL GROUPS FROM SULFUR-CONTAINING PEPTIDES BY CATALYTIC HYDROGENATION IN LIQUID AMMONIA O-tcrf-BUTYL-L-SERYL-S-tert-BUTYL-L-CYSTEINE ferr-BUTYL ESTER... 

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. 

AE Jackson, RAW Johnstone. Rapid, selective removal of benzyloxycarbonyl groups from peptides by catalytic transfer hydrogenation. Synthesis 685, 1976. 

Dimethoxy-aa-dimethyl-benzyloxycarbonyl constitutes an improvement over the 3,5-dimethoxybenzyloxycarbonyl group (see Scheme 16). The photochemical removal is easier (faster by a factor of 6), proceeding in high yield and, in numerous experiments, in quantitative yields. The group is, however, sensitive to mild acid, a disadvantage on many occasions. On the other hand, it can be photolyzed under conditions that do not affect a benzyloxycarbonyl group. 

Knudsen, K.R. and Holden, J. and Ley, S.V. and Ladlow, M. (2007). Optimization of Conditions for 0-Benzyl and A-Benzyloxycarbonyl Protecting Group Removal using an Automated Flow Hydrogenator. Synth. Catal, 349, 535-538. 

The pyrimidine ring of the title compounds (701) were formed upon condensative cyclization of anthranilic acids with the 1-benzyloxy-carbonyl-5-ethoxy-l,4-diazocine (700), followed by removal of the N-benzyloxycarbonyl group (66USP3280117). 

The benzyloxycarbonyl group, but not the tert-butoxycarbonyl group, may be removed by catalytic hydrogenation. Again a carbamic acid is formed, which readily loses C02 ... 

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. 

N-benzyloxycarbonylamino-ethyl-phosphomorpholidate 44 in pyridine solution. The pyrophosphate formed was isolated and the benzyloxycarbonyl group was removed by hdyrogenolysis. 

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 ... 

To prevent side reactions, the amino group of alanine must be protected to make it nonnucleophilic. In Section 24-7B, we saw that an amino acid reacts with benzyl chlo-roformate (also called benzyloxycarbonyl chloride) to form a urethane, or carbamate ester, that is easily removed at the end of the synthesis. This protecting group has been used for many years, and it has acquired several names. It is called the benzyloxycarbonyl group, the carbobenzoxy group (Cbz), or simply the Z group (abbreviated Z). 

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