The present invention provides for compounds useful for treating an HIV infection, or preventing an HIV infection, or treating AIDS or ARC. The compounds of the invention are of formula I wherein A is A1, A2, A3 or A4 and R.sup.1, R.sup.2, R.sup.3, R.sup.4a, R.sup.4b, R.sup.5, R.sup.6, Ar, X.sup.1, X.sup.2, X.sup.4, X.sup.4 and X.sup.5 are as herein defined. Also disclosed in the present invention are methods of treating an HIV infection with compounds defined herein and pharmaceutical compositions containing said compounds. ##STR00001##