Conformation matters: siRNAs with antisense strands with 5′-(E)-vinyl-phosphonate-α-l-LNA elicit stronger RNAi-mediated gene silencing than those with 5′-(E)-vinyl-phosphonate-LNA

RNAi-mediated gene silencing is more efficient when the antisense strand of the siRNA is modified at 5′ end with a 5′-vinyl-phosphonate carrying nucleotide that adopts a C3′- exo (south) conformation than a C3′- endo (north) pucker.