Total synthesis of the antiinflammatory and proresolving protectin D1

Resolvins, Protectins, and Maresins: DHA-Derived Specialized Pro-Resolving Mediators, Biosynthetic Pathways, Synthetic Approaches, and Their Role in Inflammation

Marine organisms are an important source of natural products with unique and diverse chemical structures that may hold the key for the development of novel drugs. Docosahexaenoic acid (DHA) is an omega-3 fatty acid marine natural product playing a crucial regulatory role in the resolution of inflammation and acting as a precursor for the biosynthesis of the anti-inflammatory specialized pro-resolving mediators (SPMs) resolvins, protectins, and maresins. These metabolites exert many beneficial actions including neuroprotection, anti-hypertension, or anti-tumorigenesis. As dysregulation of SPMs is associated with diseases of prolonged inflammation, the disclosure of their bioactivities may be correlated with anti-inflammatory and pro-resolving capabilities, offering new targets for drug design. The availability of these SPMs from natural resources is very low, but the evaluation of their pharmacological properties requires their access in larger amounts, as achieved by synthetic routes. In this report, the first review of the total organic syntheses carried out for resolvins, protectins, and maresins is presented. Recently, it was proposed that DHA-derived pro-resolving mediators play a key role in the treatment of COVID-19. In this work we also review the current evidence on the structures, biosynthesis, and functional and new-found roles of these novel lipid mediators of disease resolution.

Stereocontrolled synthesis of resolvin D1

We studied the synthesis of RvD1, a pro-resolving mediator. The intermediate containing vic-diol and enal functional groups was prepared via the oxidation of the γ,δ-epoxy alcohol followed by the epoxide ring opening in one pot. The C11-aldehyde in the resulting enal was converted to the trans iodo-olefin by reaction with TMSC(N2)Li and subsequent hydrozirconation using in situ generated Cp2Zr(H)Cl followed by iodination. The trans enynyl alcohol was synthesized by the reaction of the TMS-containing epoxy alcohol with lithium TMS-acetylide. Finally, two fragments were joined by the Sonogashira coupling, and the triple bond was reduced to afford RvD1 stereoselectively.

The Protectin Family of Specialized Pro-resolving Mediators: Potent Immunoresolvents Enabling Innovative Approaches to Target Obesity and Diabetes

A western type diet and lifestyle play an important role in the development of chronic diseases, yet little insight into the precise cellular and biomolecular mechanisms has emerged. It is known that an unbalanced diet may result in obesity and diabetes. Sufficient amounts and proper balance of omega-6 and omega-3 polyunsaturated fatty acids is key for maintenance of health. The resolution of inflammation is now held to be a biosynthetically actively driven process precisely regulated and controlled by a superfamily of specialized pro-resolving mediators. Specialized pro-resolving mediators are biosynthesized from both omega-6 and omega-3 polyunsaturated fatty acids and are resolution agonists acting on distinct G-coupled protein receptors. These mediators display potent anti-inflammatory and pro-resolving bioactions with EC₅₀-values in the low nanomolar to picomolar range. The protectin (PD) family of specialized pro-resolving mediators is biosynthesized from the two omega-3 polyunsaturated fatty acids docosahexaenoic acid (DHA) and n–3 docosapentaenoic acid (n–3 DPA). All of the PDs display interesting bioactions as anti-inflammatory and pro-resolving agents. This review covers the bioactions, G-coupled protein receptors pharmacology, biosynthesis, and medicinal chemistry of the PD family of specialized pro-resolving mediators with an emphasis on obesity and anti-diabetic effects. In order to enable drug development and medicinal chemistry efforts against these diseases, stereoselective total organic synthesis of each of these mediators is required for confirmation of structure, stereochemical biosynthesis, and their functions. We provide an overview of our ongoing efforts and the current knowledge.

Synthesis of protectin D1 analogs: novel pro-resolution and radiotracer agents

Protectin D1 is a specialized pro-resolving mediator with potent pro-resolving and anti-inflammatory effects in vivo in several human disease models. Herein the preparation of the first synthetic analog of protectin D1, named 22-F-PD1, is presented together with data from in vivo investigations. This analog showed potent pro-resolving and anti-inflammatory properties. These results inspired the preparation of the radiotracer 22-[18F]F-PD1-ME that was used in a positron emission tomography proof of concept study. Altogether, the findings presented contribute to new knowledge on the biomolecular properties of protectin D1 analogs. In addition, an improved formal synthesis of the metabolite 22-OH-PD1 is reported.

Profiling of bioactive lipids in different dendritic cell subsets using an improved multiplex quantitative LC-MS/MS method

Lipids are an energy source and key components of the cell membrane; however, they are also bioactive mediators of physiological and pathophysiological phenomena. Quantification of bioactive lipids is not easy because they have diverse chemical properties and are present in trace amounts. Here, we improved a multiplex method of quantifying bioactive lipids, thereby enabling measurement of 90 compounds simultaneously. We then used this system to quantify bioactive lipids produced by two subsets of dendritic cells (DCs): all-trans retinoic acid-treated DCs (RA-DCs) (a type of tolerogenic DC (tDC)) and conventional DCs (cDCs). We found that cDCs produced inflammatory lipid mediators such as leukotrienes, whereas RA-DCs produced anti-inflammatory lipid mediators such as prostaglandin I₂. Consistent with this, cDCs expressed larger amounts of mRNA encoding 5-lipoxygenase and LTA₄ hydrolase (both responsible for leukotriene biosynthesis) and RA-DCs produced larger amounts of mRNA encoding prostaglandin I₂ synthase. Taken together, the results suggest that the method is useful for clarifying the roles of bioactive lipids during immune responses.

Stereoselective Total Synthesis of Macrophage-Produced Prohealing 14,21-Dihydroxy Docosahexaenoic Acids

Synthesis of 14S,21R- and 14S,21S-dihydroxy-DHA (diHDHA) among the four possible stereoisomers of 14,21-diHDHA was studied. Methyl (R)-lactate (>97% ee), selected as a C20-C22 fragment (DHA numbering), was converted to the C17-C22 phosphonium salt, which was subjected to a Wittig reaction with racemic C16-aldehyde of the C12-C16 part with the TMS and TBS-oxy groups at C12 and C14, yielding the C12-C22 derivative with 14R/S and 21R chirality. Kinetic resolution using Sharpless asymmetric epoxidation of the TBS-deprotected allylic alcohol with l-(+)-DIPT/Ti(O-i-Pr)₄ afforded 14S-epoxy alcohol and 14R-allylic alcohol with >99% diastereomeric excess (de) for both. The CN group was introduced to the epoxy alcohol by reaction with Et₂AlCN. The 14R-allylic alcohol was also converted to the nitrile via Mitsunobu inversion. Reduction of the nitrile with DIBAL afforded the key aldehyde corresponding to the C11-C22 moiety. The Wittig reaction of this aldehyde with a phosphonium salt of the remaining C1-C10 part followed by functional group manipulation gave 14S,21R-diHDHA. Similarly, ethyl (S)-lactate (>99% ee) was converted to 14S,21S-diHDHA. The chiral LC-UV-MS/MS analysis demonstrated that each of these two 14,21-diHDHAs synthesized using the presented total organic synthesis was highly stereoselective and identical to the macrophage-produced counterpart.

Discovery of specialized pro-resolving mediators marks the dawn of resolution physiology and pharmacology

It is with great pleasure that I write this foreword and introduction to this Special Issue dedicated to the protective actions of the pro-resolving mediators and edited by my colleague Dr. Jesmond Dalli. Many of my collaborators and colleagues that helped to uncover the actions and clinical potential of the resolvins and other specialized proresolving mediators (SPM), namely, the superfamily of pro-resolving mediators that includes the resolvin (E-series, D-series and DPA-derived), protectin and maresin families, as well as the arachidonic acid-derived lipoxins, join me in this special issue. They have given contributions that present exciting new results on the remarkable actions and potency of these unique molecules, the SPM moving forward the importance of their mediators and pathways in human biology. Each contribution to this issue is presented by world authorities in their respective fields covering discoveries that demonstrate the importance and impact of resolution mediators in biology, medicine and surgery. While some of the authors were students and/or fellows with me and others, they are today the founding "resolutionists" of a new era of appreciation of autacoid biosynthesis and metabolomics in human health and disease with their rigorous attention to experimental detail and discovery. The chapters of this issue are filled with exciting new discoveries demonstrating the dynamics and potential of resolution mediators.

Proresolving lipid mediators and mechanisms in the resolution of acute inflammation

Inflammatory responses, like all biological cascades, are shaped by a delicate balance between positive and negative feedback loops. It is now clear that in addition to positive and negative checkpoints, the inflammatory cascade rather unexpectedly boasts an additional checkpoint, a family of chemicals that actively promote resolution and tissue repair without compromising host defense. Indeed, the resolution phase of inflammation is just as actively orchestrated and carefully choreographed as its induction and inhibition. In this review, we explore the immunological consequences of omega-3-derived specialized proresolving mediators (SPMs) and discuss their place within what is currently understood of the role of the arachidonic acid-derived prostaglandins, lipoxins, and their natural C15-epimers. We propose that treatment of inflammation should not be restricted to the use of inhibitors of the acute cascade (antagonism) but broadened to take account of the enormous therapeutic potential of inducers (agonists) of the resolution phase of inflammation.

Stereoselective synthesis of protectin D1: a potent anti-inflammatory and proresolving lipid mediator

A convergent stereoselective synthesis of the potent anti-inflammatory, proresolving and neuroprotective lipid mediator protectin D1 (2) has been achieved in 15% yield over eight steps. The key features were a stereocontrolled Evans-aldol reaction with Nagao's chiral auxiliary and a highly selective Lindlar reduction of internal alkyne 23, allowing the sensitive conjugated E,E,Z-triene to be introduced late in the preparation of 2. The UV and LC/MS-MS data of synthetic protectin D1 (2) matched those obtained from endogenously produced material.

Resolution phase lipid mediators of inflammation: agonists of resolution

Lipid mediators are appreciated for their roles in leukocyte traffic required in host defense. With identification of novel resolution phase mediators, resolvins, protectins and maresins, these three families and their aspirin-triggered forms, given their potent stereoselective actions with human cells and animal disease models, are coined specialized pro-resolving mediators (SPM). Stereochemistries of key SPM are established and several groups reported organic synthesis. Given increased availability, this two-year-review period expands their potent pro-resolving and non-redundant actions. Collectively, they support the concept that return of acute inflammation involves active biosynthesis and SPM signaling toward homeostasis.

1,5-Diphenylpent-3-en-1-ynes and methyl naphthalene carboxylates from Lawsonia inermis and their anti-inflammatory activity

Lawsonia inermis (Lythraceae) known as henna is one of the most popular and ancient plants used in cosmetics and hair dying. It is cultivated for its leaves but other parts such as seeds, flowers, stem bark and roots are also used in traditional medicine for millennia. Henna tattoo paste also proved to be beneficial for wound healing and in several skin diseases suggesting potent anti-inflammatory activity. To evaluate henna anti-inflammatory activity, 31 compounds, including three 1,5-diphenylpent-3-en-1-yne derivatives, lawsochylin A-C and three methyl naphthalene carboxylates, lawsonaphthoate A-C, were isolated from the stems and leaves of henna utilizing a bioassay-guided fractionation. The structures of the compounds were elucidated by spectroscopic data. Two compounds, lawsochylin A and lawsonaphthoate A showed potent anti-inflammatory activity by inhibition of superoxide anion generation (IC(50)=1.80 and 1.90 μg/ml) and elastase release (IC(50)=1.58 and 3.17 μg/ml) of human neutrophils in response to fMLP or cytochalasin B. Moreover, the known compounds, luteolin, apigenin, 4S-4-hydroxy-α-tetralone, and 2-butoxysuccinic acid, also showed potent inhibition of superoxide anion generation (IC(50)=0.75-1.78 μg/ml) and elastase release (IC(50)=1.62-3.61 μg/ml).