Controlled Stepwise Release of Fragrance Alcohols from Dendrimer‐Based 2‐Carbamoylbenzoates by Neighbouring Group Participation

Abstract

Keywords: Dendrimers / Fragrances / Neighboring-group effects / Kinetics / Delivery systems / Controlled release 2-Carbamoylbenzoates which are chemically bound to the surface of dendrimers were found to release tertiary fragrance alcohols by neighbouring group assisted alkaline hydrolysis under mild reaction conditions. Owing to the excellent separation of the intermediate reaction products by analytical HPLC, the kinetic rate constants of the first two consecutive reaction steps of fragrance release could be

Controlled Release of Volatiles under Mild Reaction Conditions: From Nature to Everyday Products

“…[140,141] The excellent separation of the parent dendrimer 66 from its monocyclized intermediate by HPLC allowed the determination of the rate constants for the first two cyclization steps. [141] It was shown that the release kinetics are not influenced by steric effects and are thus independent of the dendrimer size. The fact that no enzymes or other bulky reagents are needed to release the active substances from the dendrimer surface allows the preparation of large molecules Scheme 21.…”

Parameters Influencing the Release of Tertiary Alcohols from the Surface of “Spherical” Dendrimers and “Linear” Stylomers by Neighbouring‐Group‐Assisted Hydrolysis of 2‐Carbamoylbenzoates

“…[8,9] Since, for steric reasons, a larger number of molecules can be attached to the dendrimer surface than could possibly be physically trapped within the dendritic branches, the release of bioactive compounds by covalentbond cleavage from the dendrimer surface is particularly interesting for high-generation dendrimers. Redox reactions, [10][11][12] photofragmentations, [13][14][15] hydrolyses [16][17][18][19] and the action of enzymes or catalytic antibodies [20][21][22][23] were identified as the most common triggers for covalent-bond cleavage at the dendrimer surface. Besides drug delivery, this concept was also successfully used to control the release of fragrances.…”

“…Besides drug delivery, this concept was also successfully used to control the release of fragrances. [18,23,24] Water is the most important solvent for all types of biological applications, and the release of the active compound must therefore proceed in aqueous media.…”

“…[28][29][30][31] The release mechanism is pH dependent and based on the abstraction of a proton from the carbamoyl moiety under neutral or slightly basic conditions to form an intermediate nucleophile, as shown in Scheme 1. [18,30,31] The nucleophile then attacks the carbonyl group of the neighbouring ester group and releases the alcohol upon intramolecular cyclisation. Primary, secondary and even tertiary alcohols have successfully been released by using this concept, and besides monomeric or polymeric species, highly symmetric dendrimer-based 2-carbamoylbenzoates of fragrance alcohols have been prepared and analysed for their controlled-release properties.…”

“…Primary, secondary and even tertiary alcohols have successfully been released by using this concept, and besides monomeric or polymeric species, highly symmetric dendrimer-based 2-carbamoylbenzoates of fragrance alcohols have been prepared and analysed for their controlled-release properties. [18] The compounds were found to be stable in acidic aqueous media, but hydrolyse under neutral or slightly alkaline conditions to release the corresponding alcohol.…”