1. Current address: (a) Chiroscience Limited, C. S. P.M. R., Cambridge, CB4 4WE, U.K. (b) Bristol-Myers Squibb Pharmaceutical Research Institute, P.O. Box 4000, Princeton, NJ 08543-4000. (c) SmithKline Beecham Pharmaceuticals, P.O. Box 1539, King of Prussia, PA 19406-0939.