[1] NIDDK, Bioorgan Chem Lab, NIH, Bethesda, MD 20892 USA
[2] Univ Calif San Diego, Skaggs Sch Pharm & Pharmaceut Sci, San Diego, CA 92063 USA
[3] Scripps Res Inst, Dept Mol Biol, La Jolla, CA 92037 USA
[4] Scripps Res Inst, Dept Chem, La Jolla, CA 92037 USA