Patent ID: 6858722

Claim:
A method of preparing an oligomer having at least one moiety of formula: wherein: each X 1 and X 2 is, independently, O or S; Bx is a protected or unprotected heterocyclic base moiety; and R 1 is H, a protected hydroxyl group, a sugar substituent group, or a protected sugar substituent group; comprising the steps of: (a) providing a compound having one of the formulas: wherein: T 1 is a hydroxyl protecting group; and T 2 is a covalent attachment to a solid support or a solid support bound nucleoside, nucleotide, oligonucleoside or oligonucleotide; (b) removing the T 1 group to form said compound having a 5′-hydroxyl group; and (c) treating said compound having a 5′-hydroxyl group with a phosphoramidite composition to form an extended compound, said phosphoramidite composition comprising a phosphoramidite compound of the formula: wherein: T 1 is a protected hydroxyl group, a nucleoside, a nucleotide, an oligonucleoside or an oligonucleotide; R 0 is a phosphorus protecting group; and each L 1 and L 2 is, independently, C 1-6 alkyl; or L 1 and L 2 are joined together to form a 4- to 7-membered heterocyclic ring system including the nitrogen atom to which said L 1 and L 2 are attached, said ring system optionally including at least one additional heteroatom selected from O, N and S; said phosphoramidite composition further comprising at least about 1% by weight of at least one 2′-hydroxy nucleoside, a P III species different from said phosphoramidite compound where covalent attachment of groups to the P III phosphorus of said P III species is through oxygen or sulfur, or a P V species where covalent attachment of groups to the P V species is through oxygen, sulfur or nitrogen.