The present invention provides compounds of formula I where R.sup.1 to R.sup.4 are as defined herein which are useful for treating or preventing an human immunodeficiency virus (HIV) infection, or treating AIDS or ARC. The invention further provides for methods of treating or preventing HIV infection with compounds according to formula I and compositions containing the same. The invention still further provides process for the preparation of compounds of formula I wherein R.sup.4 is A.sup.1 and X.sup.1 is NH or O. ##STR00001##