Abstract: Disclosed is a composition comprising a nucleic acid and a chemical compound, said composition forming a star structure defining 3 or more stems extending from a reaction center. The stems are formed by a nucleic acid duplex and the chemical compound has been formed in the reaction center as the reaction product of 3 or more chemical groups. The advantage of the composition is that a close proximity is provided between the chemical groups in the reaction center, thereby promoting a reaction. The invention also relates to a method for preparation of the composition. The advantage of the method is that it does not require the pre-synthesis of a large number of templates and that it is not dependent upon codon/anti-codon recognition for an encoded molecule to be formed.