Triply bridged (1,3,5) cyclophanes from cystine and lanthionine linkers—a comparison

The condensation of benzene 1,3,5-tricarbonylchloride with cystine-di-Me [H2N–CH(COOMe)–CH2–S–S–CH2–CH(COOMe)–NH2] yielded triply bridged (1,3,5) cyclophane 1, which was shown by detailed spectral studies and molecular orbital calculations to have a D3 symmetry with conformationally identical linkers and a spherical topology. In sharp contrast, the (1,3,5) cyclophane 2 from the rarely studied lanthionine di-Me [H2N–CH(COOMe)–CH2–S–CH2–CH(COOMe)–NH2], showed only a equatorial twofold symmetry. This work highlights the special properties of the –S–S– bridge in cystine, which makes it an exceptional synthon in nature and organic synthesis.