Essential structural features of (2Z,4E)-5-phenylpenta-2,4-dienoic acid for inhibition of root gravitropism

Design and synthesis of strong root gravitropism inhibitors with no concomitant growth inhibition

Herein, we describe a highly potent gravitropic bending inhibitor with no concomitant growth inhibition. Previously, we reported that (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76) selectively inhibits root gravitropic bending of lettuce radicles at 5 μM. Based on the structure-activity relationship study of ku-76 as a lead compound, we designed and synthesized various C4-substituted analogs of ku-76. Among the analogs, 4-phenylethynyl analog exhibited the highest potency for gravitropic bending inhibition, which was effective at only 0.01 μM. Remarkably, 4-phenylethynyl analog is much more potent than the known inhibitor, NPA. Substitution in the para position on the aromatic ring of 4-phenylethynyl group was tolerated without diminished activity. In addition, evaluation using Arabidopsis indicated that 4-phenylethynyl analog inhibits gravitropism by affecting auxin distribution in the root tips. Based on the effects on Arabidopsis phenotypes, 4-phenylethynyl analog may be a novel inhibitor that differs in action from the previously reported auxin transport inhibitors.

New Drimane Sesquiterpenes and Polyketides from Marine-Derived Fungus Penicillium sp. TW58-16 and Their Anti-Inflammatory and α-Glucosidase Inhibitory Effects

Marine fungi-derived natural products represent an excellent reservoir for the discovery of novel lead compounds with biological activities. Here, we report the identification of two new drimane sesquiterpenes (1 and 2) and six new polyketides (3–8), together with 10 known compounds (9–18), from a marine-derived fungus Penicillium sp. TW58-16. The planar structures of these compounds were elucidated by extensive 1D and 2D NMR, which was supported by HR-ESI-MS data. The absolute configurations of these compounds were determined by experimental and calculated electronic circular dichroism (ECD), and their optical rotations compared with those reported. Evaluation of the anti-inflammatory activity of compounds 1–18 revealed that compound 5 significantly inhibited the release of nitric oxide (NO) induced by lipopolysaccharide (LPS) in RAW264.7 cells, correlating with the inhibition of expression of inducible nitric oxide synthase (iNOS). In addition, we revealed that compounds 1, 3–6, 14, 16, and 18 showed strong α-glucosidase inhibitory effects with inhibition rates of 35.4%, 73.2%, 55.6%, 74.4%, 32.0%, 36.9%, 88.0%, and 91.1%, respectively, which were comparable with or even better than that of the positive control, acarbose. Together, our results illustrate the potential of discovering new marine-based therapeutic agents against inflammation and diabetes mellitus.

Design and chemical synthesis of root gravitropism inhibitors: Bridged analogues of ku-76 have more potent activity

Previously, we found (2Z,4E)-5-phenylpenta-2,4-dienoic acid (ku-76) to be a selective inhibitor of root gravitropic bending of lettuce radicles at 5 μM, with no concomitant growth inhibition, and revealed the structure-activity relationship in this inhibitory activity. The conformation of ku-76 is flexible owing to the open-chain structure of pentan-2,4-dienoic acid with freely rotating single bonds, and the (2Z)-alkene moiety may be isomerized by external factors. To develop more potent inhibitors and obtain insight into the target biomolecules, various analogues of ku-76, fixed through conformation and/or configuration, were synthesized and evaluated. Stereochemical fixation was effective in improving the potency of gravitropic bending inhibition. Finally, we found highly potent conformational and/or configurational analogues (ku-257, ku-294 and ku-308), that did not inhibit root growth. The inhibition of root curvature by these analogues was comparable to that of naptalam.