Complex sentence: The name nucleoside phosphoramidite comes from the phosphite group that has a NH2 instead of a OH group, the "phosphate" group in normal nucleic acids is pentavalent, while here it is trivalent.
Split into simpler sentences: The name nucleoside phosphoramidite comes from the phosphite group that has an NH 2 instead of an OH group. The "phosphate" group in normal nucleic acids is pentavalent, while here it is trivalent.