Process for the preparation of ridinilazole and crystalline forms thereof

Described are processes for the preparation of 2,2'-di(pyridin-4-yl)-1H,1'H-5,5'- bibenzo[d]imidazole (which may also be known as 5,5'bis-[2-(4-pyridinyl)-1H- benzimidazole]), referenced herein by the INN name ridinilazole, and pharmaceutically acceptable derivatives, salts, hydrates, solvates, complexes, bioisosteres, metabolites or prodrugs thereof. The invention also relates to various compositions of purified ridinilazole, to various crystalline forms of ridinilazole, to processes for their preparation and to related pharmaceutical preparations and uses thereof (including their medical use and their use in the efficient large-scale synthesis of ridinilazole).