The present invention provides compounds of Formula (I): ##STR00001## or a stereoisomer or pharmaceutically acceptable salt or hydrate form thereof, wherein the variables A, B, L.sub.1, L.sub.2, X.sup.1, X.sup.2, X.sup.3, X.sup.4 and W are as defined herein. The compounds of Formula (I) are useful as selective inhibitors of serine protease enzymes of the coagulation cascade and/or contact activation system; for example thrombin, factor Xa, factor XIa, factor IXa, factor VIIa and/or plasma kallikrein. In particular, it relates to compounds that are selective factor XIa inhibitors. This invention also relates to pharmaceutical compositions comprising these compounds and methods of treating thromboembolic and/or inflammatory disorders using the same.