There is OW Circle Pacific trip but not a Circle Atlantic trip. You should price out the trip you are planning and then look at what a comparable RTW would cost. Perhaps there are some airline packages that will meet your needs. That is what a good T/A can do for you.
I'm not sure why you would want to do the R/T from Brazil rather than just complete the RTW after you finish in SA. BTW, your RTW will be four continents (Europe-NA-SA-Asia-Europe) if you choose to do it.