BINDING OF COPPER(II) TO THE CYCLIC OCTAPEPTIDE PATELLAMIDE-D

Patellamide D (patH4), a cyclic octapeptide from the ascidian Lissocli num patella, with two oxazoline and two thiazole rings, has the 24-aza crown-8 macrocyclic structure. The cyclic octapeptide forms multiple m ononuclear copper(II) complexes in which there are three nitrogen liga ting atoms, arising from a deprotonated amide and oxazoline and thiazo le rings, coordinated to the copper(II) ion. The multiple mononuclear copper(II) complexes can be ascribed to different metal binding sites in patH4; there are four in the asymmetric patH4 molecule and the bind ing of different ligands (Cl- or H2O) to the fourth equatorial coordin ation site. Patellamide D also forms three binuclear copper(II) comple xes ([Cu2(patH2)]2+, [Cu2(patH2)(OH)]+, and [CU2(patH2)(CO3)]) in whic h each copper(II) ion is coordinated by three nitrogen ligating atoms from a deprotonated amide and oxazoline and thiazole rings. The remain ing coordination sites may be occupied by either Cl- or H2O in the fir st two complexes, while carbonate is assumed, on the basis of X-my cry stallography presented in a future paper, to bridge the two copper(II) ions in the third complex. Electronic absorption, circular dichroism, electron paramagnetic resonance, and mass spectra are reported as a f unction of the concentration of base added to the copper(II) patellami de solutions.