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Parameters Influencing the Release of Tertiary Alcohols from the Surface of “Spherical” Dendrimers and “Linear” Stylomers by Neighbouring‐Group‐Assisted Hydrolysis of 2‐Carbamoylbenzoates
Author(s) -
Trachsel Alain,
de Saint Laumer JeanYves,
Haefliger Olivier P.,
Herrmann Andreas
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200801350
Subject(s) - dendrimer , chemistry , moiety , macromolecule , hydrolysis , molecule , intramolecular force , dispersity , polymer , imine , polymer chemistry , covalent bond , solubility , organic chemistry , catalysis , biochemistry
Size is not all! Investigation of the controlled release of tertiary alcohols from the surface of dendrimers and “stylomers” as polymer model systems (see scheme) showed that the polarity of the conjugates and structural modifications in close proximity to the release unit have a stronger influence on the rates of hydrolysis than the size (generation) or shape (linear or spherical) of the macromolecules.The influence of structural and physico‐chemical parameters on the release of a volatile tertiary alcohol (2‐methyl‐1‐phenyl‐2‐propanol) by neighbouring‐group‐assisted cyclisation of 2‐carbamoylbenzoates at neutral pH was investigated by comparing the covalent‐bond cleavage from the surface of linear, comblike poly(propylene imine) “stylomers” and their corresponding spherical, globular dendrimers. Determination of the kinetic rate constants for the stepwise intramolecular cyclisation of the 2‐carbamoylbenzoate moiety by using HPLC showed that the polarity of the conjugates, and thus their solubility in the aqueous reaction medium, has a stronger influence on the rates of hydrolysis than the size (generation) or shape (linear or spherical) of the macromolecules. Furthermore, structural modifications in close proximity to the release unit, such as the presence of functionalities with catalytic activity, have a strong impact on the release efficiency of the active molecules. An understanding of the physico‐chemical parameters determining the local environment of the covalent‐bond cleavage site is therefore an important prerequisite to transfer the characteristics of small molecules to larger structures such as oligomers and polymers and thus to design efficient macromolecular conjugates for the controlled delivery of bioactive compounds.