Temporary protecting group

The related 2-/-butyl derivative has also been prepared and used to advantage as a temporary protective group for the stereogenic center of amino acids during alkylations. ... 

Protecting group (Section 17.9) A temporary alteration in the nature of a functional group so that it is rendered inert under the conditions in which reaction occurs somewhere else in the molecule. To be synthetically useful, a protecting group must be stable under a prescribed set of reaction conditions, yet be easily introduced and removed. 

Unnecessary derivatization (use of blocking groups, protection/de-protection, and temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste. 

Scheme 1.4 Solid-phase synthesis of P-(l —> 6)-linked gentiotetraose employing ester groups for permanent protection, for temporary protection, and as linkage to the support.

Filter and dry. Check PEG-bound product by NMR and repeat glycosylation if necessary. Remove temporary protecting group and continue second cycle. 

H Kunz, H Waldmann, C Unverzagt. Allyl ester as temporary protecting group for the (S-carboxy function of aspartic acid. Int J Pept Prot Res 26, 493, 1985. 

CC Yang, RB Merrifield. The P-phenacyl ester as a temporary protecting group to minimize cyclic amide formation during subsequent treatment of aspartyl peptides with HF. J Org Chem 41, 1032, 1976. 

N-alkylation and N-acylation of piperazine-2,5-diones are quite common and have been routinely employed in several synthetic sequences (see Section IV,C). Such operations have also been performed as measures for the temporary protection of the nitrogen during further synthetic maneuvers in other parts of the molecule. Three different alkyl groups have been employed as such protecting groups. Kishi has used the methoxymethyl group for N-protection (potassium r-butoxide, chloro-methyl methyl ether 0°C, 75% yield). Deprotection was achieved by cone. HCl-ethanol at reflux temperature (81T2045). 

In a preparation213 of 2,3,4-tri-O-benzyl-D-galactopyranose, allyl protecting-groups were removed from 0-1 and 0-6 of allyl 6-O-allyl-2,3,4-tri-0-benzyl- -D-galactopyranoside, and the allyl group has been used214 for the temporary protection of 0-2, 0-3, 0-4, or 0-6 in benzyl... 

---