Tricyclic inhibitors of matrix metalloproteinases

A compound of Formula ##STR51## wherein ##STR52## is attached at the 1 or 2 position of the A ring;

• wherein X is
• O, or
• N--OR.sup.6 wherein R.sup.6 is
• hydrogen,
• --(CH.sub.2).sub.n -aryl wherein n is zero or an integer of 1 to 5,
• alkyl, or
• --(CH.sub.2).sub.n -cycloalkyl wherein n is as defined above;
• R and R.sup.a are each the same or different and each is
• hydrogen,
• --(CH.sub.2).sub.n -aryl wherein n is as defined above,
• --(CH.sub.2).sub.n -heteroaryl wherein n is as defined above,
• --(CH.sub.2).sub.p --R.sup.7 --(CH.sub.2).sub.q -aryl wherein R.sup.7 is O or S and p or q is each zero or an integer of 1 to 5 and the sum of p+q equals an integer of 5,
• --(CH.sub.2).sub.p --R.sub.7 --(CH.sub.2).sub.q -heteroaryl wherein p, q, and R.sup.7 are as defined above,
• alkyl,
• --(CH.sub.2).sub.n -cycloalkyl wherein n is as defined above, or
• --(CH.sub.2).sub.r --NH.sub.2 wherein r is an integer of 1 to 9;
• a is zero or an integer of 1 to 3;
• and
• R.sup.5 is
• OH, or
• NH--OR.sup.6 wherein R.sup.6 is as defined above;
• with the proviso that when X is O, and R.sup.5 is not NH--OR.sup.6, at least one of R or R.sup.a is not hydrogen;
• and corresponding isomers thereof;
• or a pharmaceutically acceptable salt thereof.