What is the best method to deprotected thio-modified oligos (10-1926)?
RESPONSE:The trityl group used to protect the thiol is not acid labile and therefore can not be removed on a DNA synthesizer using the normal acid deprotection. Cleavage of the oligonucleotide from the support and removal of the base-protecting groups are carried out with ammonium hydroxide in the normal manner. If purification is desired, it should be done before removing the trityl group. The presence of the trityl group allows standard trityl-on reverse phase (RP) purification techniques to be used. Final deblocking of the oligonucleotide involves cleavage of the trityl-sulfur bond. This is accomplished by oxidation with silver nitrate with the excess silver nitrate being precipitated with dithiothreitol (DTT). Excess DTT can be removed by extraction with ethyl acetate, by desalting or by ethanol precipitation. Procedure 1. Deprotect with ammonium hydroxide in the normal manner. 2. Purify the trityl containing oligonucleotide by HPLC or Poly-Pak cartridge. 3. Evaporate the product s
