The prior B2 denial will always be linked to his name, date of birth, photo, and other biometrics. A new Portuguese passport will not change this, so he is not eligible for ESTA. He is free to apply again for a B2, but this will be denied as well unless he strengthens his ties to Brazil. Does he own property, have a stable job, family responsibilities, etc. in Brazil? If you are a serious "friend" in the USA, and his purpose for travel is to visit you, this will be considered a strong tie to the USA, with a good chance that he will abuse the terms of the B2 and try to stay in the US, as many Brazilians before him have done. I suggest that you visit him in Brazil if your true intention is to meet in person, it is a beautiful country. Good luck!