Isaac remained with his family in Amsterdam for only one year, where he continued his studies in philosophy and Hebrew before emigrating to Brazil with his aunt and her husband Moses Raphael de Aguilar.
His parents and two younger brothers remained; one of them, David de Castro Tartas, later became notable as a printer in Amsterdam.
Against the wishes of his relatives there, he went later to Bahia de Todos os Santos, the colony's capital, where he was recognized as a Jew, arrested by the Portuguese Inquisition, and sent to Lisbon.
[1] Although a Dutch citizen, he was summoned before the tribunal of the Inquisition, where he avowed his belief in Judaism and his determination to remain true to the faith.
A memorial sermon was delivered by Saul Levi Morteira (printed at the press of Isaac's younger brother), and elegies in Hebrew and Spanish were written in his honor by Solomon de Oliveyra and Jonah Abravanel.