Abstract:

Objective: In this study, the chemical constituents of Cajanus cajan seeds and pods were separated and identified, as well as their antioxidant and anti-inflammatory activities were investigated, in order to provide a scientific basis for the discovery of new natural antioxidant and anti-inflammatory active constituents and the development and utilization of C. cajan resources. Method: The seeds and pods of C. cajan were extracted by 95% ethanol reflux, respectively, and the extracts were filtered and concentrated by reduced pressure to obtain the seed and pod residues. The residues were extracted with different organic solvents, and the ethyl acetate extraction section was further separated and purified by column chromatography techniques such as silica gel and gel. The structures of the isolated compounds were identified using MS and NMR techniques. The antioxidant activities of the isolated compounds were evaluated by measuring the scavenging capacities of DPPH free radicals. The anti-inflammatory activities of the isolated compounds were evaluated by Griess method for determining the inhibitory abilities of the compounds on the NO production in mouse macrophage RAW 264.7 induced by LPS. Result: Four compounds were isolated from the ethyl acetate extraction of C. cajan seeds and identified by ESI-MS and NMR techniques as hydroquinone (S1), 1-linoleoyl-3-palmitoyl glycerol (S2), daucosterol linoleate (S3) and stigmastane-3β,6α-diol (S4). Five compounds were isolated from the ethyl acetate extraction of C. cajan pods and preliminarily identified as flavonoids based on their physicochemical properties, and further identified by ESI-MS and NMR techniques as 2',5,7-trihydroxy-4'-methoxyisoflavone (P1), calycosin (P2), daidzein (P3), 2'-hydroxygenistein (P4) and genistein (P5). Compounds S1–S4, P1–P2 were isolated from the genus Cajanus for the first time, while compound S2 was a new compound. Antioxidant and anti-inflammatory activities studies showed that compounds S1, P1, P2, P4 had relatively strong DPPH free radical scavenging activities, with the EC₅₀ values of 63.10 ± 0.15, 64.97 ± 0.67, 79.63 ± 1.14 and 79.43 ± 1.29 μmol·L^?1, respectively, while compounds S1–S2, P1–P5 showed strong NO inhibitory activities, with the IC₅₀ values of 31.36±0.44, 52.08±1.11, 30.66±0.83, 46.30±0.90, 55.18±2.07, 44.11±0.79 and 44.92±2.24 μmol·L^?1, respectively. The antioxidant and anti-inflammatory activities of compound P1 and the anti-inflammatory activity of compound P4 were reported for the first time. Conclusion: C. cajan seeds mainly contain fatty acid and sterol derivatives, with relatively weak antioxidant and anti-inflammatory activities, while C. cajan pods contain multiple isoflavones with better antioxidant and anti-inflammatory activities. Therefore, C. cajan pods are more valuable for development and utilization, and can be used as a source of raw materials for extracting natural antioxidant and anti-inflammatory components.

Key words: Cajanus cajan seed, pod, chemical constituent, isoflavone, antioxidant activity, anti-inflammatory activity