Amino group protection

Nitro groups have been reduced to amino groups, whilst amino groups in the 3- and 6-positions of pyrido[2,3-f ]pyrazines and in the 5-position of the [3,4-f ] isomers have been hydrolyzed to the corresponding hydroxy derivatives with alkali. Protected amino groups have been liberated by hydrolysis or reduction in deazapteridine syntheses. 

II II X>- - leaving group protected amino group I 1. acetate cleavage 2. oxidation... 

Further intramolecular reaction of the poly(phenylene)-type polymer leads to more condensed polymers. Tour synthesized polymer 84 bearing a carbonyl moiety and a protected amino group in the phenylene rings by the reaction of boronate 83 and a dibromobenzene monomer. The polymerization takes place in the presence of a palladium catalyst in DME-H2O at 85 °C to give 84 that showed 3/n = 9850-28400 = 1.85-3.70) in 63-97% yields. The resulting polymer 84 is... 

Reductive Methylation of 4,4 -Dimethoxybenzhydryl-Protected Amino Groups 1140 ... 

Following a similar strategy, Miller [92] has documented the ring opening of a-azido (3-lactams with a-amino acid esters, Scheme 24. Treatment of a-azido (3-lactams 68/69 with glycine methyl ester thus afforded dipeptides 70/71 with differentially protected amino groups. From dipeptide 70, a synthesis of the rhodo-peptin B5 analogue 72 was further demonstrated. 

The self-assembled dendrimer carries 24 phthalimide groups (= protected amino groups) on its surface, which can be replaced also by other groups (e.g., dyes). Even larger structures should be available, using the whole spectrum of selectivities indicated above. 

A third amino acid synthesis begins with diethyl a-bromomalonate. First the Br is replaced by a protected amino group using the Gabriel synthesis (see Section 10.6). Then the side chain of the amino acid is added by an alkylation reaction that resembles the malonic ester synthesis (see Section 20.4). Hydrolysis of the ester and amide bonds followed by decarboxylation of the diacid produces the amino acid. An example that shows the use of this method to prepare aspartic acid is shown in the following sequence ... 

The amino group in Z-Ala is protected as the nonnucleophilic amide half of a carbamate ester. The carboxyl group can be activated without reacting with the protected amino group. Treatment with ethyl chloroformate converts the carboxyl group to a mixed anhydride of the amino acid and carbonic acid. It is strongly activated toward nucleophilic attack. 

For modified nucleosides bearing trifluoroacetyl-protected amino groups, after step 3 of Protocol 10, add one volume of 33% aqueous ammonia solution to the reaction and stir at room temperature overnight. Then evaporate the solution to an oil, redissolve in 50 mM TEAB and purify by MPLC according to Protocol 19. 

Let us briefly outline the general principles of problem solving involved in the task of synthesizing a polypeptide. The basic reaction in this synthesis is a trivial formation of an amide bond between two a-amino acids, one of which must have a protected amino group, B, and the other a protected carboxyl group, A (Scheme 3.5). Next, to obtain the tripeptide CBA it is necessary to... 

The conversion of Boc groups protecting amino groups to other more appropriate carbamate derivatives can be achieved with Ti(0-i-Pr)4 as shown in Eqs (228) and (229) [527]. If there are two Boc-amino moieties in the same molecule, that which is less hindered can be selectively converted to another carbamate group, e.g. benzoy-ioxy, as exemplified in Eq. (229). 

---