Patent ID: 8686130

Claim:
A compound comprising an unnatural base represented by Formula I: wherein, A 1 represents N or CH; A 2 represents CH; R 1 represents hydrogen or an amino group; and R 2 represents a substituent selected from the group consisting of a 2,2â€²-bithien-5-yl group, a 2-(2-thiazolyl)thien-5-yl group, a 5-(2-thienyl)thiazol-2-yl group, and a 2,2â€²,5â€²,2â€³-terthien-5-yl group; or a derivative wherein an amino group in the unnatural base is protected by a protecting group of a phenoxyacetyl group, an isobutyryl group, or a dimethyl formamidyl group; or a derivative thereof wherein the thienyl group or the thiazolyl group contained in R 2 is further substituted with a methyl group, an amino group, a hydroxyl group, or a thiol group.