One-Step Synthesis of Chiral Oxindole-type Analogues with Potent Anti-inflammatory and Analgesic Activities

Abstract

Here we report a facile approach to synthesize highly optically active oxindole-type analogues with both high yield and enantioselectivity. This single-step synthesis strategy represents a substantial improvement upon existing methods that are often involved with multi-step routes and have suboptimal atomic economy. One such compound, namely Q4c, showed remarkable in vivo anti-inflammatory activity with efficiency approaching to that of a steroidal compound dexamethasone. Moreover, Q4c alleviated pain in mouse models with comparable activity to morphine. Further investigation suggested that nitric oxide signaling pathway is involved in the anti-inflammatory and analgesic activities of Q4c. Notably, this is the first time that chiral oxindole-type analogues have been identified to be both anti-inflammatory and analgesic, and our study also paved the way for future development of oxindoles as drug candidates in this field.

Figure 1. Synthesis of optically and biologically active spirooxindole-type alkaloids by asymmetric strategies.

(A) SPX-F with antipyretic activity, three-step synthesis; (B) JP-8 g with inflammatory and anti-cancer activities, three-step synthesis; (C) proposed catalytic mechanism for the one-step synthesis of oxindoles in this study; (D) the structure of new oxindole-type molecules.

Figure 2. Synthesis of various isatylidene malononitriles under optimized conditions.

Unless noted, the reactions were conducted with 2 (0.22 mmol) and 3 (0.20 mmol) using 1.0 mol% catalyst in Et₂O for 30 min at room temperature. Yield and ee values were determined by HPLC, and configuration was assigned by comparison of retention time and specific rotation of obtained compounds with the data reported in previous literatures. See Supplementary Fig. 3 for more details.

Figure 3. Structure-activity relationship of Q series compounds.

Synthesized spirooxindole compounds (12.5 mg/kg) were tested using mouse ear inflammation model (n = 6). A steroidal anti-inflammatory drug dexamethasone (DEX, 5.0 mg/kg) was used as a reference compound.

Figure 4. The in vivo anti-inflammatory and analgesic activity of Q4c.

(A) Carrageenan-induced paw inflammation model (n = 7). (B) Xylene-induced ear inflammation model (n = 10). (C) Tail flick pain model (n = 6). (D) Acetic acid twist body pain model (n = 6). Data are expressed as mean ± SEM. Statistical evaluation was performed by two-way ANOVA, followed by Tukey post-tests (*p < 0.05; **p < 0.01; ***p < 0.005; ****p < 0.001).

Figure 5. Mechanism of actions of Q4c.

(A) The effect of Q4c on LPS-stimulated NO release from primary peritoneal macrophages. Nitrite levels were assessed by Griess reagent. Data are shown as mean ± SEM (n = 5). Significant difference between LPS and test groups are indicated, **p < 0.01; ***p < 0.001.(B) The effect of iNOS antagonist SMT on the in vivo anti-inflammatory activity of Q4c. Data are shown as mean ± SEM (n = 7). Significant difference from vehicle, *p < 0.05; **p < 0.01; ***p < 0.005; ****p < 0.001. Significant difference between Q4c treatments in the absence and presence of SMT, #p < 0.05. Statistical analysis was performed by two-way ANOVA, followed by Tukey’s post-tests.