Structural insights into Resolvin D4 actions and further metabolites via a new total organic synthesis and validation

Local production and downstream metabolism of specialized proresolving lipid mediators (SPMs) are pivotal in regulating their biological actions during resolution of inflammation. Resolvin D4 (RvD4: 4S,5R,17S-trihydroxydocosa-6E,8E,10Z,13Z,15E,19Z hexaenoic acid) is one of the more recently elucidated SPMs with complete stereochemistry biosynthesized from docosahexaenoic acid . Here, we report a new multimilligram commercial synthesis that afforded enough material for matching, validation, and further evaluation of RvD4 functions. Using LC-MS-MS profiling, RvD4 was identified at bioactive amounts in human (1 pg/mL) and mouse bone marrow (12 pg/femur and tibia). In mouse bone marrow, ischemia increased the formation of RvD4 37-fold (455 pg/femur and tibia). Two separate mouse ischemic injury models were used, where RvD4 reduced second organ reperfusion lung injury 50%, demonstrating organ protection. Structure-function relationships of RvD4 demonstrated 40% increase in neutrophil and monocyte phagocytic function in human whole blood in comparison with 2 separate trans-containing double bond isomers that were inactive. These 2 isomers were prepared by organic synthesis: 4S,5R,17S-trihydroxydocosa-6E,8E,10E,13Z,15E,19Z-hexaenoic acid (10-trans-RvD4), a natural isomer, and 4S,5R,17S-trihydroxydocosa-6E,8E,10E,13E,15E,19Z-hexaenoic acid (10,13-trans-RvD4), a rogue isomer. Compared to leukotriene B