a-amanitin and its derivatives are eight-membered, cyclic peptides that are additionally bridged with a tryptathionine cross-link. Their synthesis sometimes yields isomers, which haven't been classified unambiguously so far. Until now, it was not clear whether these isomers differing in the positioning of the trpytathionine bridge indeed exist and if yes, under which conditions they are formed and how they shall be named. In our work, we therefore investigated the occurrence of these isomers. We have identified the structure and the dynamics of the amanitin derivative 4a and its isomer 4b. Investigating the impact of the macrocyclisation site on the occurrence of this isomer, we published an optimised strategy for atroposelective synthesis (including precursors 3b and 3c). Here, we present the simulated structures of the ansamers 4a and 4b, which both are in very good agreement to crystal data, together with the precursors 3b and 3c. 4a and 4b are the amanitin derivatives, for whose classification we propose the term ansamers. For further instructions, please refer to 'README'. For the files required to reproduce the MD simulations, please refer to the Zenodo repository 'MD setup data for ansamer amanitin derivatives and precursors for atroposelective synthesis' available under DOI: 10.5281/zenodo.7125315.