Synthesis of Ether-Linkage-Based Cyclic Glycerophospholipid Carrying Methylene Moiety that Improves Membrane Fluidity

Abstract

A cyclic glycerophospholipid, in which two glycerols are connected via alkyl chains to form a 64-membered macrocycle, was synthesized. The structural features that differentiate this from our analogous lipids previously reported are two methylene moieties in the alkyl chains, which were incorporated to improve membrane fluidity. Fluorescence recovery after photobleaching revealed that the membranes made from the methylene-containing cyclic lipid demonstrated fluidity at room temperature unlike those of a linear alkyl-chain lipid of equal ring size.

Key words

lipids - macrocycles - ether lipid - phospholipid - cyclic lipid - FRAP

References and Notes

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17

Selected Physical Data of 9
^¹H NMR (400 MHz, CDCl₃): δ = 1.30 (12 H, br s), 1.36 (6 H, s), 1.42 (6 H, s), 1.52 (8 H, quint, J = 5.4 Hz), 1.96-2.02 (8 H, m), 1.58 (8 H, br m), 2.26 (8 H, br m), 3.39-3.53 (8 H, m), 3.72 (2 H, dd, J = 8.2, 6.4 Hz), 4.05 (2 H, dd, J = 8.2, 6.4 Hz), 4.26 (2 H, quint, J = 6.0 Hz), 4.69 (4 H, br s). ESI-MS (TOF): m/z = 694 [M + Na⁺], 672 [M + H⁺].

18

Selected Physical Data of 10
^¹H NMR (400 MHz, CDCl₃): δ = 1.32 (12 H, br s), 1.42 (4 H, quint, J = 7.2 Hz), 1.53 (8 H, quint, J = 3.4 Hz), 1.59 (4 H, quint, J = 7.0 Hz), 1.98-2.02 (8 H, br s), 2.28 (4 H, br m), 3.45-3.56 (8 H, m), 3.66 (2 H, dd, J = 11.4, 5.0 Hz), 3.73 (2 H, dd, J = 11.5, 4.1 Hz), 3.87 (2 H, quint, J = 4.7 Hz), 4.71 (4 H, br s). ESI-MS (TOF): m/z = 614 [M + Na⁺], 591 [M + H⁺].

19

Selected Physical Data of 11
^¹H NMR (400 MHz, CDCl₃): δ = 1.28 (12 H, br s), 1.40 (4 H, quint, J = 7.1 Hz), 1.51 (8 H, quint, J = 4.2 Hz), 1.96-1.99 (8 H, br m), 2.25 (4 H, br m), 2.42 (2 H, d, J = 4.6 Hz), 3.19 (4 H, qd, J = 7.6, 5.4 Hz), 3.40-3.54 (8 H, m), 3.94 (2 H, sext, J = 5.1 Hz), 4.69 (4 H, br m), 7.22 (6 H, t, J = 7.3 Hz), 7.29 (12 H, t, J = 7.3 Hz), 7.42 (12 H, d, J = 7.3 Hz). ESI-MS (TOF): m/z = 1098 [M + Na⁺].

20

Procedure for the Preparation of 13
To a solution of Cu(OAc)₂ (314 mg, 1.73 mmol) in refluxing pyridine (100 mL), a solution of 12 (257 mg, 0.173 mmol) in pyridine (10 mL) was added dropwise with a syringe pump over 5.5 h. The solution gradually turned from blue to dark green. After completion of the addition the solution was heated at the same temperature for 1 h. The mixture was cooled to r.t. and evaporated to give a residue, which was purified on a silica gel column chromatography eluted with hexane-EtOAc (10:1) to give 13 as a yellow oil; yield 157 mg (61%).
^¹H NMR (400 MHz, CDCl₃): δ = 1.28 (24 H, br s), 1.39 (8 H, br m), 1.51-1.57 (16 H, br m), 1.96-2.01 (16 H, m), 2.28 (br s, 8 H), 3.13-3.20 (4 H, br m), 3.39 (4 H, br t, J = 6.9 Hz), 3.45-3.58 (10 H, m), 4.68 (8 H, br s), 7.20 (6 H, t, J = 7.1 Hz), 7.27 (12 H, t, J = 7.3 Hz), 7.45 (12 H, d, J = 7.8 Hz). ESI-MS (TOF): m/z = 1505 [M + Na⁺].

21

The sequence from 7 and glycerol moiety to 12 was altered from the one we previously reported for preparing a straight-chain analogue 1.^¹0,¹¹ At the step of the connection of chain moiety and protected glycerol in the previous study, we used 1-trityl-3-p-methoxybenzoyl-sn-glycerol, which was prepared by starting from 1,2-isopropylidene-sn-glycerol in three steps. Through this modification, several protection-deprotection steps could be omitted. The order in which the chains was introduced into the glycerol moiety was also changed. This change would cause an increase in the steric hindrance around the secondary hydroxy groups during the Williamson reaction sequence; however, the reaction proceeded without difficulties even though the yield of 12 was somewhat lower.

22

Purification of 2 was conduced on an LC-908 instrument (Japan Analytical Industries) equipped with a JAIGEL-GS310 column [eluent, CHCl₃-MeOH = 1:2 (v/v)].
Colorless gummy oil. ^¹H NMR (400 MHz, CDCl₃-CD₃OD = 2:1): δ = 1.30 (28 H, br s), 1.41 (12 H, br s), 1.52 (20 H, br s), 1.97-2.01 (16 H, t, J = 7.6 Hz), 2.27 (8 H, br m), 3.23 (18 H, s), 3.38-3.49 (6 H, m), 3.55-3.61 (12 H, m), 3.88 (4 H, br s), 4.25 (4 H, br s), 4.70 (8 H, br s). ESI-MS (TOF): m/z = 1350 [M + Na⁺], 1328 [M + H⁺].