Characterization of novel aminobenzylcantharidinimides and related imides by proton NMR spectra and their effects on NO induction

Various acidic anhydrides including cantharidin were converted into corresponding aminobenzylcantharidinimide 3a and analogous imides 3b∼k (at the ortho, meta, and para positions) with 35%∼87% yields by reacting with aminobenzylamines and triethylamine. The two methyl side chains of cantharidinimides 3ao, 3am, and 3ap, and related imides had more than two chiral centers; the lone pair of electrons of nitrogen displayed a different chemical shift and coupling constant in H-NMR spectra when the amino group of benzylamine was in the ortho position. These cantharidinimides had parent aniline, pyridine, and naphthalene plane structures, and the primary amine nucleophilicity and basicity might reflect the inductive electron's negative effect on chemical shifts. We prepared cantharidinimides by heating the reactants cantharidin 1a, aliphatic and aromatic acid anhydrides, primary benzylic amines, and aniline derivatives to ca. 200 °C with 3 mL of dry toluene, and 1∼2 mL of triethylamine in high-pressure sealed tubes (Buchi glasuster 0032) to produce cantharidinimides and their analogues in good yields. The para-aminobenzylic imides showed greater inhibition of nitric oxide (NO) synthesis by NO synthase (NOS) than did ortho- and meta-aminobenzylic imides. Compound 3fp, para-aminobenzylic norbonane-imide, had the most potent effect on inducible NOS among the tested compounds and showed 35% inhibition. Cantharidinimides and their analogue were prepared by heating the reactants cantharidin, aliphatic, aromatic acid anhydrides, and primary benzyl amines, aniline derivatives with 3 mL of dry toluene, and 1-2 mL of triethylamine in high-pressure sealed tube at 200 ^oC in good yields. The para-aminobenzylic imides showed greater inhibition of nitric oxide (NO) synthesis by NO synthase (NOS) than that of ortho- and meta-aminobenzylic imides did.