Design, Synthesis, and Evaluation of Antinociceptive Properties of Novel CBD-Based Terpene-Cinnamoyl-Acyl-Hydrazone Analogues

Abstract

Background/Objectives: Cannabidiol (CBD) has been reported for its antinociceptive, anti-inflammatory, and neuroprotective activities. However, several legal restrictions on its medicinal uses and even research have contributed to the development of synthetic analogues. Therefore, the aim of this study was the design and synthesis of a novel series of CBD-based structural analogues, and the in vivo evaluation of their potential antinociceptive activity. Methods: Using a two-step synthetic route, 26 new terpene-cinnamoyl acyl-hydrazone analogues were obtained and were submitted to in vivo screening in the classical formalin-induced paw edema and hot plate assays. Results: The compounds PQM-292, PQM-293, PQM-295, PQM-307, PQM-308, and PQM-309 exhibited the best results in the neurogenic phase (first phase) of the formalin-induced licking response, showing comparable results to morphine. Notably, in the inflammatory phase (second phase), compound PQM-292 exhibited the best anti-inflammatory activity. Interestingly, in the hot plate model, six other compounds (PQM-274, PQM-291, PQM-294, PQM-304, PQM-305, and PQM-378) showed the best antinociceptive activity in comparison to morphine, especially PQM-274, which exhibited an antinociceptive effect almost equivalent to the reference drug. Interestingly, these findings suggested that these bioactive compounds, despite their structural similarity, act through different mechanisms, which were investigated by molecular docking with CB1, CB2, and TRPV1 receptors. In silico results indicated that the most active compounds should act through different mechanisms, probably involving interactions with TRPA1. Conclusions: Therefore, due to the promising antinociceptive activity observed for these highlighted compounds, particularly for PQM-292 and PQM-274, without apparent toxicity and psychoactive effects, and the possible involvement of diverse mechanisms of action, these compounds could be considered as promising starting points to the development of new drug candidate prototypes of clinical interest.

Keywords: CBD analogues; acute pain; antinociceptive activity; bioactive acyl-hydrazone derivatives; cannabidiol-based analogues.

Figure 1

Chemical Structures of (−)-CBD (1), HU-443 (2), HU-308 (3), DMH-CBD (4), (+)-CBD (5), and H2-CBD (6).

Figure 2

Rational structural design of a new series of the CBD-based terpene-cinnamoyl-N-acyl-hydrazone analogues.

Figure 3

Synthetic route for the preparation of the terpene-cinnamoyl-N-acyl-hydrazones 10a–m and 11a–m.

Figure 4

Antinociceptive effect of compounds on the licking response induced by formalin in mice. Animals were pretreated with different doses of vehicle, morphine (5 µmol/kg), acetylsalicylic acid (ASA, 1100 µmol/kg), or compounds (10 µmol/kg), 60 min before the injection of formalin (2.5%/paw). The results are presented as mean ± SD (n = 5 per group) of the time that the animal spent licking the capsaicin-injected paw. One-way or two-way analysis of variance (ANOVA) followed by Tukey’s post hoc test was used for unpaired data when more than two groups were compared to the same control. The post hoc tests were run only if F achieved the necessary level of statistical significance. * When p was lower than 0.05, group differences were considered significant.

Figure 5

Effects of compounds in the thermal-induced nociception (hot plate model). Animals were orally pretreated with morphine (9 µmol/kg), compounds (10 µmol/kg), or vehicle. The results are presented as mean ± SD. (n = 7–10 per group). The area under the curve was calculated by GraphPad Prism Software 10.1.2. One-way or two-way analysis of variance (ANOVA) followed by Tukey’s post hoc test was used for unpaired data when more than two groups were compared to the same control. The post hoc tests were run only if F achieved the necessary level of statistical significance. * When p was lower than 0.05, group differences were considered significant.

Figure 6

Docking results for CB1 receptor. For the PQM compounds: C atoms are represented in grey, O atoms in red, H atoms in white, and N atoms in blue. (A) Interactions of compound PQM-275 (10b) with residues of HIS-75, PHE-97, PHE-165, VAL-93, and LEU-173; (B) interactions of PQM-375 (10k) with residues of VAL-93, MET-239, ILE-164, ALA-248, SER-251 (H-bond interaction), and PHE-5 (H-bond interaction); and (C) interactions of CBD with residues of PHE-67, PHE-74, PHE-165, PHE-247, SER-251 (H-bond interaction), ILE-164, and HIS-75. Structural residues according to Liu et al. [24]: F170^2.57, 174^2.61, F177^2.64, and H178^2.65. Residues F200^3.36 and W356^6.48 also seem to play a role in the activity.

Figure 7

Distinct positions predicted for compounds PQM-375 (10k), PQM-304 (11h), and PQM-292 (11d) in the docking results for CB1. For the PQM compounds: C atoms are represented in grey, O atoms in red, H atoms in white, and N atoms in blue.

Figure 8

Predicted positions of PQM-276 (11b), PQM-295 (10e), and PQM-290 (11c) in the docking results for CB2 receptor, highlighting H-bond interactions of PQM-295 and PQM-290 with THR93 residue. For the PQM compounds: C atoms are represented in grey, O atoms in red, H atoms in white, and N atoms in blue.

Figure 9

Predicted positions for compounds PQM-376 (11k) and PQM-295 (10e) in the docking results for the TRPV1 receptor. For the PQM compounds: C atoms are represented in grey, O atoms in red, H atoms in white, and N atoms in blue.