may designate oxo thioxo imino or optionally substituted methylene or together may form a spiro biradical consisting of a 1 5 carbon atom s alkylene chain which is optionally interrupted and or terminated by one or more heteroatoms groups selected from u2014 o u2014 u2014 s u2014 and u2014 nr n u2014 where r n is selected from hydrogen and c 1 4 alkyl and where two adjacent non geminal substituents may designate an additional bond resulting in a double bond and r n when present and not involved in a biradical is selected from hydrogen and c 1 4 alkyl and basic salts and acid addition salts thereof throughout the examples herein the term u201c lna u201d locked nucleoside analogues refers to the bi cyclic nucleoside analogues incorporated in the oligomer and having a 2 u2032 0 4 u2032 c methylene beta d ribofuranose configuration u s pat no 6 268 490 another lna variant is the u03b1 l lna monomer which is disclosed in the international patent application publication no wo 00 66604 the entire content of which is incorporated here in by reference when used herein u03b1 l lna monomers include such compounds having the following general formula ii wherein x.