Complex sentence: He entered in the Xanthopoulon monastery in Istanbul, from which he took the surname.He worked aside with Gennadius Scholarius during the Council of Florence and in that frame he was one of the signatories of a 1445 document against the East-West union of Churches.
Split into simpler sentences: He entered in the Xanthopoulon monastery in Istanbul, from which he took the surname. Isidore worked aside with Gennadius Scholarius during the Council of Florence and in that frame he was one of the signatories of a 1445 document against the East-West union of Churches.