Boc-group

To illustrate the specific operations involved, the scheme below shows the first steps and the final detachment reaction of a peptide synthesis starting from the carboxyl terminal. N-Boc-glycine is attached to chloromethylated styrene-divinylbenzene copolymer resin. This polymer swells in organic solvents but is completely insoluble. ) Treatment with HCl in acetic acid removes the fert-butoxycarbonyl (Boc) group as isobutene and carbon dioxide. The resulting amine hydrochloride is neutralized with triethylamine in DMF. 

Like the benzyloxycarbonyl protecting group the Boc group may be removed by treat ment with hydrogen bromide (it is stable to hydrogenolysis however)... 

Protect glycine as its Boc derivative and anchor this to the solid support Remove the pro tecting group and treat with Boc protected phenylalanine and DCCI Remove the Boc group with HCl then treat with HBr in tnfluoroacetic acid to cleave Phe Gly from the solid support... 

Walter H. Whitlock Edward F. Ezell Shuen-Cheng Hw g The BOC Group, Inc. 

The principal international producers and distributors of nitrogen are L Air Liquide S.A. (France), The BOC Group Pic (U.K.), Air Products and Chemicals, Inc. (U.S.), and Praxair, Inc. (U.S.). There are many other smaller regional producers. 

HCl, Et20, 6 h, 83-88% yield.Acidic deprotection of the BOC group could not be achieved with complete selectivity in the presence of an MTM ester. The trityl and NFS (2-nitrophenylsulfenyl) groups were the preferred nitrogen protective groups. 

AcOH, HBr, 10°, 10 min, 70% yield. Phthaloyl or trifluoroacetyl groups on amino acids are stable to these conditions benzyloxycarbonyl (Cbz) or /-butoxycarbonyl (BOC) groups are cleaved. 

The Tcrom ester is prepared from the cesium salt of an N-protected amino acid by reaction with 2-(trifluoromethyl)-6-chromylmethyl bromide (DMF, 25°, 4 h, 53-89% yield). Cleavage of the Tcrom group is effected by brief treatment with n-propylamine (2 min, 25°, 96% yield). It is stable to HCl/dioxane, used to cleave a BOC group. ... 

The BOC group is used extensively in peptide synthesis for amine protection. It is not hydrolyzed under basic conditions and is inert to many other nucleophilic reagents. 

BOC-OC6H4S Me2 MeSO. ", H20. This is a water-soluble reagent for the introduction of the BOC group. 

The BOC group can be cleaved with TBDMSOTf and the intermediate silyl carbamate converted to other nitrogen protective groups. 

The Adoc group is very similar to the r-BOC group in its sensitivity to acid, but often provides more crystalline derivatives of amino acids. 

The Moz group is more readily cleaved by acid than is the benzyloxycarbonyl or BOC group.The section on benzyl carbamates should be consulted since many of the methods for formation and cleavage should be applicable to the Moz group as well. 

The Mpt and Ppt derivatives can be prepared from an amino acid and the thio-phosphinyl chloride (Me2PSCl or Ph2PSCl, respectively, 41-78% yield, lysine gives 16% yield)." The Mpt group is cleaved with HCl or Ph P- HCl and is cleaved 60 times faster than the BOC group. The Ppt group is the more stable of the two groups. 

The BOC group has been introduced onto the imidazole nitrogen of histidine with BOCF (pH 7-8), BOCN3, MgO, and (B0C)20. ° It can be introduced onto pyrroles and indoles with phenyl /-butyl carbonate and NaH, 67-91% yield, or with NaH, BOCN3. ... 

The N " -BOC group can be removed under the usual conditions for removing the BOC group CF3COOH and HF. It can also be removed with hydrazine and NH3/ MeOH. NaOMe/MeOH/THF has been used to remove the BOC group from pyrroles in 66-99% yield. Thermolysis at 180° cleaves the BOC group from indoles and pyrroles in 92-99% yield. 

The Adoc group can be cleaved by the same methods used to cleave the BOC group. The Adoc group is somewhat more stable than is the BOC group to acid. 

It should be noted that when a BOC-protected amide is subjected to MeONa treatment the amide bond is cleaved in preference to the BOC group (85-96% yield) because of the difference in steric factors. The BOC group can be removed by the methods used to remove it from simple amines. 

In a study of the deprotection of the MEM ethers of hydroxyproline and serine derivatives, it was found that the MEM group was stable to conditions that normally cleave the t-butyl and BOC groups [CF3COOH, CH2CI2, 1 1 (v v)]. The MEM group was also stable to 0.2 N HCl, but not stable to 2.0 N HCl or HBr-AcOH. ... 

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