| Research Abstract |
Solid phase synthesis on the polystyrene resin is devoid of sufficient chemical reactivity to allow the preparation of the complex organic molecules. Gold nanoparticles functionalized with self-assembled monolayers (SAMs) of organothiols are inherently nanoscopic entities that provide a scaffold for the attachment of organic molecules. We report a first step in a program of research aimed at using the gold nanoparticles as a tool for solid phase synthesis of a various organic molecules.
To examine the gold nanoparticles as a support for the solid phase synthesis of the peptides, we prepared the various Fmoc amino acids (Gly, Ala, Val, Leu, Phe, IIe, Trp) having alkanethiols at C-terminal. Reduction of HAuCl_4, with NaBH_4 in MeOH in the presence of the Fmoc amino acids resulted in the formation of Au nanoparticles coated with Fmoc amino acids shells. The Au nanoparticles are stable and can be characterized by NMR and IR. Loading amount of the amino acids are determined by treatment of the Au nanoparticles with I_2, which cleaves Au-S bonds to give the amino acids as disulfide forms. The loading amounts of the Gly, Ala, Val, Phe, Trp containing thiols on gold are 0.55, 1.22, 0.78, 0.88, 0.71 mmol/g.respectively. The Fmoc Ala on gold nanoparticles is easily dispersed in CHCl_3 and CH_2Cl_2 and aggregated in MeOH and Ether,
Then, coupling of the Fmoc Ala on gold nanoparticles with a various Fmoc amino acids is examined. After deprotection of Fmoc group in Ala, coupling of Fmoc protected Ala, Val, Leu, Phe, IIe, and Trp with DIPC and HOBt in CH_2Cl_2 at room temperature gave the Ala-Ala, Ala-Val, Ala-Leu, Ala-Phe, Ala-IIe, and Ala-Trp dipeptides in 97%, 95%, 95%, 77%, 96%, and 98% yields, respectively.
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