Acylating agents, selectivity, cyclic

Several research groups have used cyclic acetals for studying the selectivity of acylating agents, for example, benzoyl chloride-pyri-... 

The selectivity of acylations or alkylations of polyamines can also be modulated by protonation [78] or by conversion to cyclic aminals [71, 79, 80]. The latter strategy has, for instance, been used successfully for the preparation of monofunctionalized 1,4,7-triazacyclononanes (Scheme 10.18). In this reaction the first alkylation leads to the formation of an amidinium salt, which is more difficult to alkylate than a tertiary amine. Thus, the use of only one equivalent of alkylating agent leads to a clean monoalkylation. 

Some examples of C3 symmetrical compounds are known. Valinomycin, a cyclic peptide lactone antibiotic, is a highly selective K -carrier. It consists of a cyclic trimer containing L-valine, D-a-hydroxyisovaleiic acid (Hyi), D-valine and L-lactate. The C3 symmetrical agent enter-obactin is a cyclic lactonic 7V-acylated serine trimer. 

A variety of acylation reactions of chitosan are possible by using different acyl-ating agents, such as aliphatic carboxylic acid chlorides (hexanoyl, dodecanoyl and tetradecanoyl chlorides), cyclic anhydrides and cyclic esters. The acylation reaction is not regioselective. When IV,0-acylated chitosans were prepared with acyl chlorides in methanesulfonic acid [62-63], the derivatives of 4-chlorobutyl and decanoyl chlorides showed higher fungidal activities than chitosan [64]. Selectively N-acylated chitosan have been obtained by Lee et al. [65-66] with butanoic, hexanoic and benzoic anhydride under homogeneous conditions... 

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