Synthesis, Structural Confirmation, and Biosynthesis of 22-OH-PD1n-3 DPA

Abstract

PD1_{n-3 DPA} belongs to the protectin family of specialized pro-resolving lipid mediators. The protectins are endogenously formed mediators that display potent anti-inflammatory properties and pro-resolving bioactivities and have attracted interest in drug discovery. However, few studies have been reported of the secondary metabolism of the protectins. To investigate the metabolic formation of the putative C22 mono-hydroxylated product, coined 22-OH-PD1_{n-3 DPA}, a stereoselective synthesis was performed. LC/MS-MS data of synthetic 22-OH-PD1_{n-3 DPA} matched the data for the biosynthetic formed product. Cellular studies revealed that 22-OH-PD1_{n-3 DPA} is formed from n-3 docosapentaenoic acid in human serum, and we confirmed that 22-OH-PD1_{n-3 DPA} is a secondary metabolite produced by ω-oxidation of PD1_{n-3 DPA} in human neutrophils and in human monocytes. The results reported are of interest for enabling future structure-activity relationship studies and provide useful molecular insight of the metabolism of the protectin class of specialized pro-resolving mediators.

Keywords: 22-OH-PD1n-3 DPA; biosynthesis; natural products; omega oxidation; polyunsaturated fatty acids; protectins; specialized pro-resolving mediators; stereoselective synthesis; structural elucidation.

Figure 1

Overview of families of specialized pro-resolving mediators (SPMs) derived from eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), arachidonic acid (AA), and n-3 docosapentaenoic acid (DPA).

Figure 2

Chemical structures of some n-3 DPA derived SPMs. Where known, the absolute configuration is included.

Scheme 1

Established biosynthesis of 2 [20,21] and putative formation of 22-OH-PD1_{n-3 DPA} (5).

Scheme 2

Synthesis of 22-OH-PD1_{n-3 DPA} (5).

Figure 3

Multiple reaction monitoring (MRM) chromatogram of the products from (A) endogenous 22-OH-PD1_{n-3 DPA} (5) produced in human serum; (B) synthetic material of 5; (C) co-injection of endogenous and synthetic material.

Figure 4

MRM chromatogram of the products from (A) human neutrophils incubated with vehicle; (B) human neutrophils incubated with PD1_{n-3 DPA} (2); (C) co-injection of samples obtained from (A,B).

Figure 5

PD1_{n-3 DPA} (2) was converted to 22-OH-PD1_{n-3 DPA} (5) by human monocytes. Multiple reaction monitoring chromatograms for m/z 377 > 361 of the products obtained from (A) human monocytes incubated with PD1_{n-3 DPA}; (B) synthetic 22-OH-PD1_{n-3 DPA}.