Hm, them I hope you know almost all of old citizens of Belgrade and the area around Belgrade, although they weren't numerous, were re-allocated to Istanbul, and Belgrade was repopulated from other parts of Balkans later on. So it is true, some parts of Ottoman empire had Slavic blood, but they are outside of modern Slavic borders.

Interesting thing is that people, or more probably smal remnant of them survived untill 1912, and were returned back in Serbia. Famous Serbs from Galipolje. Interesting fact, that their dialect, altough verry archaic, and preserved from XV century, was essentialy just part of Shtokavian dialect.