Ratio of POSP formation in PS-T5-mer synthesis using thymidine phosphoramidite dissolved in THF containing peroxide.

Entry	Solvents	BHT	THF peroxide (mM)	POSPsa (%)
1	MeCN	—	0	2.5
2	25% THF in MeCN	—	<0.1	2.4
3	25% THF in MeCN	○	4.6	2.3
4	THF	—	<0.1	3.3
5	THF	○	4.6	2.5

^aConversion ratio to POSP was calculated from the UV area ratio of the HPLC analysis.