Cassane diterpenoids were successfully and simultaneously identified in Caesalpinia minax Hance by high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry. A total of 59 peaks were detected, and among them 51 compounds, including 41 furanocassane diterpenoids, 10 furanolactone cassane diterpenoids were simultaneously identified and characterized on the basis of the protonated molecule, retention behavior, and fragments in MS(2) . Ten compounds, including seven novel compounds, were identified or tentatively identified for the first time in C. minax. In a positive ion mode, the fragmentation pathways of cassane diterpenoids were also analyzed for the first time. The relative amounts of the five main diterpenoids (caesalpinin L, caesalpinin F2 , bondcellpin C, caesalpinin E, and ξ-caesalmin) were simultaneously quantified by high-performance liquid chromatography. Results showed that the newly discovered and known components of C. minax can be used to determine the material basis of bioactivity; this method can also be applied to analyze cassane diterpenoids in herbal medicines from the genus Caesalpinia belonging to the family Fabaceae.

Cassane skeletons are rare in nature, but often possess valuable medicinal properties. A furanoditerpenoid with an unusual A-seco-rearranged cassane skeleton, neocaesalminin A, and five furanoditerpenoids were isolated from seeds of Caesalpinia minax Hance, along with six known cassane derivatives, 7-O-acetyl-bonducellpin C, caesalmin F, caesalmin C, ζ-caesalmin, caesalmin E1 and caesalpinin K. Compound structures were determined by spectroscopy (HR-ESI-MS, UV, IR, 1D NMR, 2D NMR), X-ray crystallography and quantum chemical computation of electronic circular dichroism). Three of the previously known compounds exhibited significant inhibition of nitric oxide production of RAW264.7 macrophages stimulated by lipopolysaccharide (LPS).

An unprecedented trinorcassane diterpenoid and a cassane furanoditerpenoid were isolated from the seeds of Caesalpinia minax. It is the first example of dicylic cassane-type trinorditerpenoid, which is different from reported 16- or 17-norcassane diterpenoids. The structure of the compounds was elucidated on the basis of 1D and 2D NMR analysis. Biosynthesis pathways are postulated, and this pathway was supported by semi-synthesis.

A bioassay-guided study led to the isolation of seven new cassane furanoditerpenes, designated as spirocaesalmin B (1), caesalpinin M1 (2), caesalpinin M2 (3), caesalmin E1 (4), caesalmin E2 (5), caesalmin E3 (6), caesalpinin F1 (7) and three known compounds neocaesalpin A(8), neocaesalpin L(9), neocaesalpin L1(10) from the seeds of Caesalpinia minax Hance. Compound structures were determined on the basis of extensive spectroscopic analyses, including X-ray crystallographic analysis, HRESI-MS, UV, IR, 1D and 2D NMR (HSQC, HMBC, NOESY) methods. Some absolute configurations were confirmed via the circular dichroism (CD) spectra. Compound 1 is the first example of an A-seco-rearranged cassane furanoditerpene with an unusual skeleton isolated from the genus Caesalpinia. All compound inhibitory effects on influenza virus neuraminidase (NA) in vitro were valued for the first time. Compared with the positive control (Zanamivir), new compounds were found to show moderate inhibitory activity.