1. L.I. Kruse et al. J. Med. Chem. 32, 409, (1989) 2. H. Guo et al. J. Med. Chem. 45, 2056, (2002) 3. H.H. Wassermann et al Tet. 58, 7177, (2002) 4. Y. Shai et al. Biochemistry 28, 4801, (1989) 5. M. McWatt, G.J. Boons, R. Kuroda Eur. J. Org. Chem., 2535, (2001)