Microwave-assisted functionalization of solid supports: application in the rapid loading of nucleosides on controlled-pore-glass (CPG)☆
Graphical abstract
Microwave-assisted rapid, and efficient functionalization of solid support and loading of nucleoside is described.
Section snippets
Microwave-assisted amination (MAA) of CPG
Using reported procedures,10, 11, 12 we attempted the amination of CPG (500 A, Prime Synthesis) by treatment with (3-aminopropyl)triethoxysilane (APTES) in toluene for 48–72 h, followed by capping of unreacted hydroxy groups with trimethylsilyl chloride. Although aminopropyl-CPG 1 could be isolated from the reaction, the heterogeneous amination reaction had to be performed in refluxing toluene and was unmanageable. Also, on some occasions, after capping of unreacted hydroxyl groups with
Microwave-assisted succinylation (MAS) of aminated CPG (1) with succinic anhydride
Encouraged by the success in MAA of CPG, the MAS of the functionalized support 1 (Fig. 1) were attempted under microwave conditions. Microwave-assisted reaction of 1 with succinic anhydride, without the aid of any solvent, resulted in a very dark yellow colored support, probably due to the formation of imide rather than the expected acid. Nevertheless, MAS of 1 (50–100 g scale) was achieved successfully to give 2, in the presence of catalytic amount of DMAP in DMF as solvent, in less than 5 min.
Coupling of nucleoside to the succinylated CPG (2)
With the succinylated support 2 in hand, we carried out the loading of nucleosides using EDC, DMAP, and TEA (Fig. 1). When 2 was mixed with 5′-O-DMT-deoxyadenosine (3, B = dA), DMAP, TEA, and EDC (in that order) in anhydrous pyridine and shaken in an orbital shaker, CPG 4 with high nucleoside loadings of 70–75 μmol/g was obtained. Similar results were obtained with 5′-O-DMT-T (3, B = T).
In separate experiments, we have found that anhydrous DMF could be used instead of pyridine for the loading of
Synthesis of oligonucleotides
The CPG-loaded nucleoside 4 prepared as above and the corresponding CPG prepared by conventional method10, 11, 12, 13 was employed in the 10 μmol synthesis of di-, and 20-mer oligonucleotide (PO and PS) in an Expedite Synthesizer using phosphoramidite chemistry.8 In both instances, the stepwise coupling yields was greater than 98% (as ascertained by trityl analysis). Following the synthesis, each of the CPG was treated with 28% NH4OH at 55 °C for 12 h to isolate the fully deprotected di-, and
Acknowledgements
Support of this research from the National Institutes of Health, under a Research Project Cooperative Agreement Grant Award 5 UO1 AI058270-02, is gratefully acknowledged.
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