Probing the Interactions of Thiazole Abietane Inhibitors with the Human Serine Hydrolases ABHD16A and ABHD12.

12-Thiazole abietanes are highly selective reversible inhibitors of hABHD16A that could potentially alleviate neuroinflammation. In this study, we used synthetic chemistry, competitive activity-based protein profiling, and computational methodologies to try to establish relevant structural determinants of activity and selectivity of this class of compounds for inhibiting ABHD16A over ABHD12. Five compounds significantly inhibited hABHD16A but also very efficiently discriminated between inhibition of hABHD16A and hABHD12, with compound 35 being the most effective, at 100 µM (55.1 ± 8.7%; p < 0.0001). However, an outstanding switch in the selectivity toward ABHD12 was observed in the presence of a ring A ester, if the C2' position of the thiazole ring possessed a 1-hydroxyethyl group, as in compound 28. Although our data were inconclusive as to whether the observed enzyme inhibition is allosteric or not, we anticipate that the structure-activity relationships presented herein will inspire future drug discovery efforts in this field.

Pyrazine-Fused Triterpenoids Block the TRPA1 Ion Channel in Vitro and Inhibit TRPA1-Mediated Acute Inflammation in Vivo.

TRPA1 is a nonselective cation channel, most famously expressed in nonmyelinated nociceptors. In addition to being an important chemical and mechanical pain sensor, TRPA1 has more recently appeared to have a role also in inflammation. Triterpenoids are natural products with anti-inflammatory and anticancer effects in experimental models. In this paper, 13 novel triterpenoids were created by synthetically modifying betulin, an abundant triterpenoid of the genus Betula L., and their TRPA1-modulating properties were examined. The Fluo 3-AM protocol was used in the initial screening, in which six of the 14 tested triterpenoids inhibited TRPA1 in a statistically significant manner. In subsequent whole-cell patch clamp recordings, the two most effective compounds (pyrazine-fused triterpenoids 8 and 9) displayed a reversible and dose- and voltage-dependent effect to block the TRPA1 ion channel at submicromolar concentrations. Interestingly, the TRPA1 blocking action was also evident in vivo, as compounds 8 and 9 both alleviated TRPA1 agonist-induced acute paw inflammation in mice. The results introduce betulin-derived pyrazine-fused triterpenoids as promising novel antagonists of TRPA1 that are potentially useful in treating diseases with a TRPA1-mediated adverse component.

Synthesis of 7ß-hydroxy-8-ketone opioid derivatives with antagonist activity at mu- and delta-opioid receptors.

Despite extensive years of research, the direct oxidation of the 7,8-double bond of opioids has so far received little attention and knowledge about the effects of this modification on activity at the different opioid receptors is scarce. We herein report that potassium permanganate supported on iron(II) sulfate heptahydrate can be used as a convenient oxidant in the one-step, heterogeneous conversion of Δ7,8-opioids to the corresponding 7ß-hydroxy-8-ketones. Details of the reaction mechanism are given and the effects of the substituent at position 6 of several opioids on the reaction outcome is discussed. The opioid hydroxy ketones prepared are antagonists at the mu- and delta-opioid receptors. Docking simulations and detailed structure-activity analysis revealed that the presence of the 7ß-hydroxy-8-ketone functionality in the prepared compounds can be used to gain activity towards the delta opioid receptor. The 7ß-hydroxy-8-ketones prepared with this method can also be regarded as versatile intermediates for the synthesis of other opioids of interest.

Discovery of 12-Thiazole Abietanes as Selective Inhibitors of the Human Metabolic Serine Hydrolase hABHD16A.

Screening of an in-house library of compounds identified 12-thiazole abietanes as a new class of reversible inhibitors of the human metabolic serine hydrolase. Further optimization of the first hit compound lead to the 2-methylthiazole derivative 18, with an IC50 value of 3.4 ± 0.2 µM and promising selectivity. ABHD16A has been highlighted as a new target for inflammation-mediated pain, although selective inhibitors of hABHD16A (human ABHD16A) have not yet been reported. Our study presents abietane-type diterpenoids as an attractive starting point for the design of selective ABHD16A inhibitors, which will contribute toward understanding the significance of hABHD16A inhibition in vivo.