The present invention relates to a process for preparation of triazolo[4,5-d] pyrimidine cyclopentane compounds of formula (I), and pharmaceutically acceptable salts thereof. The invention also provides novel compounds that can be used as intermediates in the process for preparing triazolo[4,5-d] pyrimidine cyclopentane compounds. The process and the intermediates are particularly useful for the preparation of ticagrelor and pharmaceutically acceptable salts thereof.