Side reactions of onium coupling reagents BOP and HBTU in the synthesis of silica polymer supports

Introduction. We have recently reported the application of phosphonium and uronium acti vating reagents to the preparation of silica poly mer supports for solid phase oligonucleotide syn thesis [1]. Both elongation of the polyamide link ers and attachment of nucleosides to the poly mers were performed in the presence of onium coupling reagents BOP and HBTU originally developed for peptide synthesis. However, the issue of possible side processes associated with these reagents has not been addressed in that paper. Here we report on the study of side reac tions of onium salts in the silica functionalisation. Materials and methods. 2 (1H Benzotriazol 1 yl) 1,1,3,3 tetramethyluronium hexafluorophos phate (HBTU), benzotriazol 1 yloxytris(dime thylamino)phosphonium hexafluorophosphate (BOP) and anhydrous 1 hydroxybenzotriazole (HOBT) were purchased from Aldrich, Fmoc glycine, piperidine and N,N diisopropylethy lamine (DIPEA) were from Fluka, 1 methylimi dazole (MeIm) was obtained from Merck. Other reagents and solvents were from domestic suppli ers. DIPEA and piperidine were distilled from NaOH, dimethylformamide and MeIm were dis tilled in vacuum. Absolute acetonitrile was pre pared by distillation over P2O5 and then from CaH2. Fmoc group loading was determined by the treatment of carefully weighed polymer sample with 20 % piperidine solution in DMF for 15 min and measuring UV absorbance at 302 nm, according to [2]. Spectral measurements were performed with Specord UV Vis spectropho tometer (Carl Zeiss Jena, Germany). Silochrom 2 silica was functionalised by aminopropyltriethoxysilane in ethanol as previ ously described [3, 4] to provide aminopropyl polymer 1 containing 125 μmol/g of the amino group. For the linker elongation, 1 g of the silica 1, Fmoc glycine (445 mg, 1.5 mmol), BOP (663 mg, 1.5 mmol), HOBT (203 mg, 1.5 mmol) and DIPEA (870 μl, 5 mmol) were agitated in DMF (10 ml) for 3 hours at ambient temperature. The polymer was filtered off, washed with DMF (3x10 ml) and CH3CN (3x10 ml) and treated with a solution of © L. V. Dubey, I. Ya. Dubey, 2005 * Corresponding author. Tel.: +38044 5265598 E mail address: [email protected] Ukrainica Bioorganica Acta 1 (2005) 13—19