Discovery of deoxylimonin δ-lactam derivative with favorable anti-inflammation and antinociception efficacy from chemical modified limonin/deoxylimonin analogs.

Chemical modifications on the A ring of limonin (1) and deoxylimonin (2) afforded 28 structural characterized derivatives, which were firstly subjected to preliminary in vivo analgesic and anti-inflammatory screen by mice model. The most promising candidate, deoxylimonin analog II-B-2 (70 mg/kg) with 3,4-dimethoxyphenylethyl moiety substitued δ-lactam in the A ring, exhibited better analgesic activity than aspirin (200 mg/kg) and stronger anti-inflammatory efficacy than naproxen (150 mg/kg). Further in vivo evaluation confirmed its advantage over limonin and showed dose-response dependent manner, and follow-up research suggested that the anti-inflammatory effect of compound II-B-2 may be attributed to the downregulation of cyclooxygenase 2 expression and the suppression of prostaglandin E2 formation.