Protecting moieties

The (/ (-enantiomer of 5-amino-2,2-dimethyl-4-phenyl-l,3-dioxane has also been successfully used for asymmetric Strecker syntheses4In addition, the acetal protecting moiety of the auxiliary has been modified. No significant change in the Strecker syntheses of a-mcthylamino nitriles has been reported for these alternative auxiliaries50. 

We chose trimethylsilyloxy group as a protecting moiety for the phenol groups because it is easy to release after or during polymerization. Speier has reported that both ethy ldimethyloxy-p-tr imethylsi lylbeitzene and... 

Although acetal-derived anions are more unstable than the corresponding thioacetals, the final hydrolysis of the protecting moiety can be performed under milder conditions. 

Mildness and Miscellaneous Reactions. The mildness of the lipases has been particularly well suited in transformations involving labile compounds that are likely to undergo decomposition when conventional chemical methods are applied, such as the long-chain polyunsaturated to-3-type fatty acids and highly labile prostaglandin precursor derivatives. Under mild conditions, lipase was exploited to hydrolyze the peracetal protected hydroperoxy derivative in eq 18 to afford the corresponding acid without affecting the peracetal protection moiety. ... 

Here it is worth noting that, while removal of the phthalimido group (as a protection moiety) can generally be accomplished by the use of hydrazine hydrate, the attempted... 

An efficient procedure for debenzylation of esters under solvent-free conditions has been reported by Varma et al. (Scheme 8.7) [42]. By altering the surface characteristics of the solid support cleavage of the 9-fluorenylmethoxycarbonyl (Fmoc) group and related protected amines can be achieved in a similar fashion. The optimum conditions for cleavage of N-protected moieties are use of basic alumina and an irradiation time of 12-13 min at - 130-140 °C. 

Features Monofunctional reactive protecting moieties by forming acetals with alcohols and acylals with carboxylic acids Properties Colorless clear liq. b.p. 147 C Rapi-Cure DDVE [ISP]... 

For this reason the biphenyl-isopropyloxycarbonyl (Bpoc) group [101], which can be cleaved completely within 15 min by 0.5% trifluoroacetic acid in dichloromethane (Fig. 35), was developed and reconunended. Yet in the meantime, in several laboratories this protecting moiety was found too labile to be of practical use in extended gel phase n-theses, since the acidity of Bpoc-amino acids themselves is sufficient to deprotect the molecule autoacidolytically. 

Therefore, a search for chemically different principles to cleave the bond anchoring a peptide to its support and to deprotect side chain functions is recommended. In the author s opinion the final entire deprotection of a synthesized peptide should be separated from the chemical operation to release a peptide from gel phase into real solution. Either all protecting moieties should be cleaved and washed-out of the polymer prior to the detachment of the peptide or the completely shielded end product should be released... 

---