Abstract: A method of purifying a hydrophobically substituted polynucleotide by reverse phase HPLC is described. The hydrophobic substituent may be removed from the polynucleotide under non-acidic conditions; the purification method is thus especially useful for acid sensitive polynucleotide analogs.

Abstract: A solid support having surface-attached carboxylic acid groups is reacted with an isoxazolium salt to form an activated support having enol ester and sulfonate groups. After washing to remove residual isoxazolium salt and base, the activated support is dried. A polypeptide is covalently or non-covalently bound to the support. The resultant immobilized polypeptide can be conveniently sequenced by N- and C-terminal sequencing methods. The support can be a polyvinylidene difluoride membrane or a glass fiber membrane having surface attached carboxylic acid groups, and the enol and sulfonate groups are provided by reacting the support with 2-ethyl-5'-phenylisoxazolium sulfonate. The dry support can be stored for at least about 3 months to achieve a peptide immobilization yield that is substantially the same as the yield obtained in the absence of drying.