The Natural Product Magnolol as a Lead Structure for the Development of Potent Cannabinoid Receptor Agonists

<div><p>Magnolol (4-allyl-2-(5-allyl-2-hydroxyphenyl)phenol), the main bioactive constituent of the medicinal plant <i>Magnolia officinalis</i>, and its main metabolite tetrahydromagnolol were recently found to activate cannabinoid (CB) receptors. We now investigated the structure-activity relationships of (tetrahydro)magnolol analogs with variations of the alkyl chains and the phenolic groups and could considerably improve potency. Among the most potent compounds were the dual CB₁/CB₂ full agonist 2-(2-methoxy-5-propyl-phenyl)-4-hexylphenol (<b>61a</b>, <i>K</i>_i CB₁∶0.00957 µM; <i>K</i>_i CB₂∶0.0238 µM), and the CB₂-selective partial agonist 2-(2-hydroxy-5-propylphenyl)-4-pentylphenol (<b>60</b>, <i>K</i>_i CB₁∶0.362 µM; <i>K</i>_i CB₂∶0.0371 µM), which showed high selectivity versus GPR18 and GPR55. Compound <b>61b</b>, an isomer of <b>61a</b>, was the most potent GPR55 antagonist with an IC₅₀ value of 3.25 µM but was non-selective. The relatively simple structures, which possess no stereocenters, are easily accessible in a four- to five-step synthetic procedure from common starting materials. The central reaction step is the well-elaborated Suzuki-Miyaura cross-coupling reaction, which is suitable for a combinatorial chemistry approach. The scaffold is versatile and may be fine-tuned to obtain a broad range of receptor affinities, selectivities and efficacies.</p></div

Activities of Magnolol Derivatives and Standard Compounds at human GPR18 and GPR55.^a

<p>Activities of Magnolol Derivatives and Standard Compounds at human GPR18 and GPR55.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077739#nt104" target="_blank">a</a>}</p

Structures of selected cannabinoid receptor ligands.

<p>Structures of selected cannabinoid receptor ligands.</p

Radioligand binding results of key compounds 61, 61a, 61b.

<p>Concentration-dependent inhibition of specific [³H]CP55,940 binding by <b>61</b> (▪) at membrane preparations of CHO cells expressing (A) human CB₁, or (B) human CB₂ receptors, respectively (<i>K</i>_i CB₁∶0.145 µM, CB₂∶0.0294 µM). The biphenol <b>61</b> is substituted with two alkyl residues, a propyl residue at one side and a hexyl chain at the other side of the biphenylic core. Each alkyl side chain is located in the <i>para</i>-position of one of the phenolic hydroxyl groups. Substitution of the hydroxyl group in the <i>para</i>-position of the propyl residue (<b>61a</b> (▾)) resulted in a remarkable increase in (A) CB₁ receptor affinity (<i>K</i>_i: 0.00957 µM), while (B) CB₂ receptor affinity was barely affected (<i>K</i>_i: 0.0238 µM) compared to the parent compound <b>61</b>. An introduction of a methoxy group in <i>para</i>-position of the hexyl side chain (<b>61b</b> (•)) had different effects: (A) <b>61b</b> displayed a moderately decreased CB₁ receptor affinity (<i>K</i>_i: 0.313 µM) and (B) a drastical loss in CB₂ receptor affinity (<i>K</i>_i: 0.281 µM) compared to <b>61</b>. Data points represent means ± SEM of three independent experiments, performed in duplicates.</p

Effects of 61, 61a and 61b on forskolin(10 µM)-induced cAMP production.

<p>CHO cells expressing (A) human CB₁, or (B) human CB₂ receptors. The maximal effect of the full agonist CP55,940 is represented by the green triangle symbol (▾). Data points represent means ± SEMs of three independent experiments, performed in duplicates.</p

Synthesis of intermeditates.

<p>(a) Br₂, NaHCO₃, CHCl₃, 0°C; (b) three steps, (1) <i>n</i>-butyllithium, Et₂O, −78°C; (2) B(OCH₃)₃, Et₂O, −78°C to rt; (3) HCl, Et₂O; (c) CH₃I, NaOH, benzyl-tri-<i>n</i>-butylammonium bromide, CH₂Cl₂ : H₂O (1∶ 1), 12 h, rt.</p

Synthesis of magnolol derivatives and analogs.

<p>(a) Pd(PPh₃)₄, Na₂CO₃, toluene, EtOH, H₂O, 100°C, 18h; (b) CH₂Cl₂, BBr₃, −78°C to rt.</p

Potencies and Efficacies of Magnolol Derivatives and Analogs at human Cannabinoid Receptor Subtypes.^a

<p>Potencies and Efficacies of Magnolol Derivatives and Analogs at human Cannabinoid Receptor Subtypes.^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077739#nt101" target="_blank">a</a>}</p

Structural comparison of Δ⁹-THC (1), the synthetic CP55,940 (4), tetrahydromagnolol (12).

<p>Structural comparison of Δ⁹-THC (1), the synthetic CP55,940 (4), tetrahydromagnolol (12).</p

Biocatalytic Conversion of Carrageenans for the Production of 3,6-Anhydro-D-galactose

Marine biomass stands out as a sustainable resource for generating value-added chemicals. In particular, anhydrosugars derived from carrageenans exhibit a variety of biological functions, rendering them highly promising for utilization and cascading in food, cosmetic, and biotechnological applications. However, the limitation of available sulfatases to break down the complex sulfation patterns of carrageenans poses a significant limitation for the sustainable production of valuable bioproducts from red algae. In this study, we screened several carrageenolytic polysaccharide utilization loci for novel sulfatase activities to assist the efficient conversion of a variety of sulfated galactans into the target product 3,6-anhydro-D-galactose. Inspired by the carrageenolytic pathways in marine heterotrophic bacteria, we systematically combined these novel sulfatases with other carrageenolytic enzymes, facilitating the development of the first enzymatic one-pot biotransformation of ι- and κ-carrageenan to 3,6-anhdyro-D-galactose. We further showed the applicability of this enzymatic bioconversion to a broad series of hybrid carrageenans, rendering this process a promising and sustainable approach for the production of value-added biomolecules from red-algal feedstocks