Protection 2-adamantyl esters

The r-butyl ester is a relatively hindered ester, and many of the methods reported below should be—and in many cases are—equally effective for the preparation of other hindered esters. The related 1- and 2-adamantyl esters have been used for the protection of aspartic acid. ... 

Protection of carboxyl groups as 2-adamantyl esters COOR - COOH... 

Adamantoate esters, to protect alcohols, 100 1-Adamantyl carbamates, to protect amines, 330, 335, 388... 

The 2-(l-adamantyl)prop-2-yl [1-(1-adamantyl)- -methylethyl] ester is resistant to catalytic hydrogenation and is removable by mild acid treatment.P These esters are prepared by reaction of Z-protected amino acids with 2-(l-adamantyl)prop-2-ene in the presence of sulfuric acid. The 2-(l-adamantyl)prop-2-yl ester is stable under conditions required for cleavage of the Al -Fmoc and Al -Nps groups and are hydrolyzed by treatment with 3% TFA in CH2Q2 which leaves fcrf-butyl esters and even Boc groups largely intact. 

For chain-elongation steps with Fmoc-Arg(Adoc)2-OH standard activation procedures are applied, such as active esters and the symmetric anhydride method, but even for the use of more powerful acylating agents, e.g. phosphonium and uronium salts, there are no contraindications. Final deprotection is performed using TFA under standard conditions of Fmoc/tBu chemistry. Properties similar to the Adoc group have been reported for iso-bornyloxycarbonyl protection, whereas increased acid lability is obtained with the 1-(1-adamantyl)- -methylethoxycarbonyl group. ... 

Peptide synthesis, N-protection Acetic-formic anhydride. Adamantyl chloroformate. Benzylthiocarbonyl chloride. /-Butoxycarbonyl-N-hydroxysuccinimide ester. /-Butyl azido-formate. /-Butylcarbonic diethylphosphoric anhydride. /-Butyl fluoroformate. /-Butyl oxycarbonyl fluoride. /-Butyl pentachlorophenyl carbonate. /-Butyl 2,4,5-trichlorophenyl carbonate. Carbobenzoxy chloride. 3,5-Dimethoxybenzyl p-nitrophenyl carbonate. [2-(Diphenyl)isopropyljphenyl carbonate. /-Pentyl chloroformate. 

Sn 1-active alkyl halides require longer reaction times (typically 3-6 h), and the yields are lower. f-Butyl chloride and adamantyl bromide have been used successfully, but the generality of the procedure needs to be demonstrated (eq 4). In contrast, acylation reactions using a wide variety of carboxylic acid chlorides have been carried out (eq 5). The initial products are protected forms of Q ,/3-diketo esters which can be isolated in yields of 72-93%. Deprotection is accomplished using MeOH/HCl. The products are vicinal tricarbonyl compounds having the usual characteristic chemical properties such as rapid formation of hydrated derivatives. The protected forms can be used directly in the synthesis of heterocycles. ... 

---