Masao Morita

Although 4-Me₂NC₅H₄N (DMAP) is a standard base for esterification of (2-Me-6-NO₂-C₆H₃CO)₂O (MNBA), N-methylimidazole (NMI) was examined for the condensation of acids with 1-stearoyl-lysophosphatidylcholine because of the non-tailing nature of NMI on silica gel. Acids tested were EPA, α-linolenic acid, TBS ethers of 18-HEPE and ricinoleic acid, acid-labile epoxy acids, and a phenyldiynyl acid. The condensation proceeded well with these acids, and chromatographic separation of resulting phosphatidylcholines and remaining NMI was easily performed. During the characterization of the products by ¹³C NMR spectroscopy, ¹³C–¹⁴N and ¹³C–³¹P couplings were observed.

Two trans-enynyl alcohol intermediates corresponding to the C1–C8 and C13–C22 parts of resolvin D6 (RvD6) were prepared through the Hudrlik–Peterson reaction of the TMS-substituted trans-epoxy alcohols with TMS-acetylide and subsequent TMS-desilylation. These intermediates were coupled with a 1,4-dihalo-2-butyne derivative under copper catalysis, and the resulting acetylene was reduced with Zn(Cu/Ag) to afford the TBS ether of RvD6 methyl ester. Desilylation with TBAF yielded the γ-lactone of RvD6, which was hydrolyzed to RvD6. The total yield of RvD6 was 1.9% in 19 steps from (3-trimethylsilyl)propargyl alcohol. The TBS ether of RvE2 methyl ester was also synthesized.

Investigation of the copper-catalyzed coupling reaction of 2-pyridinesulfonates with Grignard reagents revealed that reactions with catalytic Cu(OTf)₂ were completed in <40 min. The results differed from those of the previous CuI-catalyzed reactions of tosylates in the presence of additives (LiOMe and TMEDA) for 12–24 h. It was shown that the preferred coordination of the leaving group to the reagents accelerated the reaction. Successful reagents were MeMgCl and other RMgX. Complete inversion was established.

As an extension of the study on the Hudrlik–Peterson reaction of trans-TMS-epoxy alcohols with lithium acetylides, four cis-TMS-epoxy alcohols possessing different alkyl substituents were subjected to the reaction with TMS-acetylide. The reaction completed in 1 h at 0 °C to afford cis-enynyl alcohols in good yields. The results indicated that cis-TMS-epoxy alcohols had higher reactivity than the trans-isomers. Anions derived from 1-heptyne and phenylacetylene participated in the reaction as well. The reaction was applied to optically active cis-TMS-epoxy alcohols, and the resulting enynyl alcohols were transformed to the synthetic intermediates of protectin D1, maresin 1, resolvin E1, and leukotriene B₄.

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.

14S,22-Dihydroxy-docosa-4Z,7Z,10Z,12E,16Z,19Z-hexaenoic acid (maresin-L1) and 14R,22-dihydroxy-docosa-4Z,7Z,10Z, 12E,16Z,19Z-hexaenoic acid (maresin-L2) were chemically synthesized. They were identical to activated macrophage-produced counterparts and their total synthesis was highly stereoselective, as revealed by chiral LC-UV-MS/MS analysis. The synthesis involved the following steps: (1) kinetic resolution of a racemic allylic alcohol by the asymmetric epoxidation; (2) transformation of the epoxy alcohol to γ-hydroxyenal derivative; and (3) the Wittig reaction to furnish the Z-olefin.

A reaction of epoxy alcohols (anti and/or syn isomers) ­derived from (E)-TMS-CH=CHCH(OH)R with TMS-C≡CLi in THF/HMPA s­tereoselectively afforded (E)-TMS-C≡C-CH=CHCH(OH)R. The (E) stereo­chemistry was independent of the anti/syn stereochemistry, but the syn isomers showed higher reactivity than the anti isomers. The reaction was applied to the synthesis of (18R)- and (18S)-HEPE.

The stereoselective synthesis of resolvin D4 (RvD4) was achieved using the Wittig reaction of the C1-C10 dienal with the known C11-C22 phosphonium salt. The (S,E)-enantiomer (S)-10, corresponding to the C1-C8 part, was synthesized in 95% ee by the asymmetric transfer hydrogenation reaction of the corresponding acetylenic ketone followed by Red-Al reduction. Sharpless epoxidation of this alcohol using Ti(O-i-Pr)4/L-(+)-DIPT as a catalyst produced anti epoxy alcohol with >99% ee as the sole product in 82% yield. A subsequent functional group manipulation, including removal of the PMB group, produced the alcohol, which upon Swern oxidation afforded anti 4-hydroxy-5-TBS-oxy enal via epoxide ring opening of the resulting aldehyde. The Horner-Wadsworth-Emmons reaction was used to add the C9-C10 enal part to this aldehyde, and the resulting dienal was subjected to the Wittig reaction with C11-C22 phosphonium salt to furnish the entire structure of RvD4. Conversion of the primary alcohol to the methyl ester and deprotection of the three TBS groups with TBAF afforded 5,17-dihydroxy-γ-lactone, which was hydrolyzed to RvD4. Additionally, anti-4,5-dihydroxydodecanoic acid, a model compound of RvD4, in CD3OD was observed to be stable at room temperature for several weeks, whereas 20% of the acid in CDCl3 was converted into the γ-lactone after 24 h at rt.