Crystal structure of the pyridine salt of gambogic acid

Pyridinium gambogate, (C5H6N)(+)(C(3)8H(4)3O(8))(-), crystallizes in space group P2(1)2(1)2(1) with cell parameters a = 9.536(3) Angstrom, b = 18.502(4) Angstrom, c = 22.223(4) Angstrom, Z = 4. The X-ray structural analysis [R(F) = 0.098 for 1714 data with I greater than or equal to sigma(I); wR(F-2) = 0.157 for all 3874 independent data] confirms the structure assigned to gambogic acid on the basis of NMR analysis and of the X-ray structure of isomorellin p-bromobenzenesulfonate. A hydrogen bond links the pyridinium nitrogen atom to a carboxylate oxygen atom. The gambogate ion has two distinct faces that differ in polarity. The hydrophobic face is dominated by the alkenyl chains attached to C(2) and C(17) and a segment of the polycyclic ring system. The hydrophilic face includes the carboxylate ion and several oxygen atoms.