Yes, Portugal had already managed to build several outposts along Africa's shores before 1492. Newitt has written an excellent book on the subject, as have Earle & Lowe (eds).
https://www.amazon.com/Portuguese-West-Africa-1415-1670-Documentary/dp/0521159148
https://www.amazon.ca/Black-Africans-Renaissance-Europe-Earle/dp/0521176603