When did Denmark lose control of Frederiknagore?
Serampore:  It was part of Danish India under the name Frederiknagore from 1755 to 1845. Danish India:  For this reason their presence was tolerated until 1845, when their alliance with a defeated France led to the colony being ceded to the British East Indian company.
until 1845, when their alliance with a defeated France led to the colony being ceded to the British East Indian company.