Chemistry Reference
In-Depth Information
FIGURE 2.7
Supramolecular assembly of discrete dendrimers.
acid, G3-COOH. However, isolation of the third- and fourth-generation dendrons
required the use of preparative GPC, resulting in low yields and difficulty in a large-
scale synthetic use.
2.3.1.1 Facile Synthetic Route by Convergent Method Recently, we reported
rapid synthesis of a perfectly branched third-generation polyamide dendrimer by the
convergent method without repetitive protection-deprotection procedures, leading to
a decrease of number of steps to half of that required in conventional dendrimer
formation (Scheme 2.8) [22]. This synthesis utilizes a two-step method that consists
of the activation of carboxylic acids and condensation with an unprotected AB
2
-
building block having diamine moieties, 3,5-bis(4-aminophenoxy)benzoic acid,
using the activating agent diphenyl(2,3-dihydro-2-thioxo-3-benzoxazolyl)phospho-
nate (DBOP). In this approach, all-generation dendrons and dendrimers are prepared
using slightly excess amount of former generation dendrons to achieve the formation
of perfectly branched structures. AB
2
-building block
reactedwith acetic acid as the
terminal unit in the presence of DBOP and TEA to yield G1 dendron. Both activation
and condensation reactions were conducted in one pot for 1 h at 25
C. The reaction
mixture was diluted with methanol and poured into water, producing G1 dendron in
90% yield. G2 and G3 dendrons also can be prepared by the same coupling method.
Furthermore, all products were purified simply only by reprecipitation technique to
remove the impurities including former generation dendrons and the leaving group of
the reaction in excellent yields.
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