Large-scale purification of unstable, water-soluble secologanic acid using centrifugal partition chromatography.

Introduction: Secologanic acid, a major secoiridoid in the flower buds of Lonicera japonica, is a fragile, highly polar compound that readily changes to epivogeloside or vogeloside after being dissolved in methanol. Thus, it is very difficult to obtain secologanic acid on a large-scale.

Objective: To develop a centrifugal partition chromatography (CPC) method for large-scale purification of secologanic acid with high purity from the flower buds of L. japonica.

Methods: After fractionation with Diaion HP-20 macroporous resin, 30% methanol eluent was purified by CPC with a ternary biphasic solvent system with ethyl acetate/isopropanol/water (6:4:10, v/v/v). CPC was performed separately twice with the same solvent system, first in descending mode and second in ascending mode.

Results: After the first CPC operation, a secologanic acid enriched fraction (586 mg) was obtained from 3 g of crude extract, and secologanic acid (206 mg) was isolated with a purity over 93% in the subsequent ascending mode with the same solvent system from a 586 mg enriched fraction. In addition, it was confirmed that epivogeloside and vogeloside were reversely converted to secologanic acid in an aqueous acidic solution.

Conclusion: These results demonstrate that CPC is a simple, effective, and rapid method for the purification of secologanic acid in the flower buds of L. japonica.