Benzyloxycarbonyl amine protective group

Boc) and 7V-(benzyloxycarbonyl) (Z) protective groups are stable under these conditions. In contrast to that, the jV-(4-methoxybenzyloxycarbonyI) (Moz) protecting group can readily be cleaved by the cation radical of tris(2,4-dibromophenyl)amine (Table 11, No. 13) ° >. 

The benzyloxycarbonyl protecting group for amines is introduced in high yield using benzyl imidazole-carboxylate with a catalytic amount (5%) of dimethylamino-pyridine.[1953... 

N-Acylation and 3-alkoxycarbonylation reactions may be achieved by conventional acylation procedures. A variety of 3-acyl derivatives 157 can be prepared most conveniently by the treatment of DPPOx 266 with carboxylic acids in the presence of a tertiary amine. tert-Butoxycarbonyl (Boc-Ox, 236) and benzyloxy carbonyl (Cbz-Ox, 267) (Cbz = benzyloxycarbonyl) compounds are of practical use for introduction of nitrogen protecting groups. ... 

The first procedure is the selective protection of an amine in the presence of an indole-NH group or an alcohol.14 Indole-NH (pKa = 17) shows a similar acidity to that of alcohols (pKa = 18). In the next step the benzyloxycarbonyl (CBZ) protected compound 26 is treated with di-fcrt-butyldicarbonate (B0C)20 and DMAP to form 27. Tert-butylchloroformate is unstable and therefore cannot be used for the preparation of BOC derivatives. Conversion of 10 with (B0C)20 in the presence of DMAP would lead to the double BOC protected compound 28. 

Another protecting group often employed for amines is the benzyloxycarbonyl group. The chemistry here is reminiscent of that of the BOC group in that the amine is protected by conversion to a carbamate. This time an acyl chloride derivative, car-bobenzoxy chloride, rather than an acid anhydride derivative, is reacted with the amine. 

Butyl chloroformate reacts with cysteine to protect both the amine and thiol groups as with N,S-bis(benzyloxycarbonyl)cysteine, selective or simultaneous removal of the N- or S-protective groups can be effected.1... 

One of the syntheses mentioned there started with 3-pyrazolidinone 236, which was protected as the benzyloxycarbonyl derivative 237 in order to obtain selective N-alkylation at position 8 yielding compound 238 after removal of the protecting group. Addition of the resulting amine 238 to l-octyne-3-one 239 formed the enone 240 with the complete diazaprostanoid skeleton. Katalytic... 

Amino protecting groups fall into four broad categories nitrobenzyl (e.g., nitrobenzyloxy-carbonyl and 4,5-dimethoxy-2-nitrobenzyloxycarbonyl), phenacyl (e.g., 4-methoxyphen-acyloxycarbonyl), benzyloxycarbonyl (e.g., a,a-dimethyl-3,5-dimethoxybenzyloxycarbonyl), and arylsulfonamides (e.g., tosyl). All but the sulfonamides mask the amino group as a carbamate. Removal of the blocking moiety releases an unstable carbamic acid, which spontaneously decarboxylates to give the unprotected amine. 

The -nitrobenzyl ester of cephalosporin has been cleaved cathodically to yield cephalosporin [65]. The widely used benzyloxycarbonyl protecting group for amines is cathodically removed, giving free amine, CO2, and toluene [66] ... 

For the reversible immobilization of amines to such linkers, the most frequently used strategy is conversion of the hydroxymethyl linkers into activated carbonic esters (Figure 14.7) [8, 39, 40]. These react with primary and secondary amines or hydrazines to form immobilized carbamates or carbazates analogous to the classical benzyloxycarbonyl protecting group. Amines and hydrazides attached by this strategy to Wang resin can be cleaved with TFA [8, 40]. 

In the procedure presented here, the phthaloyl group is chosen as an amino protecting group to avoid internal amine participation.13 Amine diprotection is necessary since the same reaction conducted on the N-benzyloxycarbonyl (NHCbz) and the N-tert-butyloxycarbonyl (NHBoc) analogues did not led to clean a-chlorination but rather to unidentified products. This protection was performed using a standard procedure.14... 

Cleavage of p-nitrobenzyl group. Protection of carboxylic acids and amines as the esters and carbamates can take advantage of the selective reduction-induced fragmentation by zinc dust, as C=C bonds, S-N bonds, benzyloxycarbonyl, and diphenylmethyl groups are not affected during the operation. 

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