|Budget Amount *help
¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 2000 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1999 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1998 : ¥2,200,000 (Direct Cost : ¥2,200,000)
Archaea including methanogens, extreme halophiles, extreme thermophiles and thermoacidophiles grow under rather extraordinary conditions and have structurally unique membrane lipids to adapt the extreme environments. The lipids are consisted of hydrophobic isoprenoid chains linked to glycerol with the ether bonds, which are well contrast to the ester linkage of the eubacterial and eukaryotic membrane lipids. The most striking feature of the archaeal ether lipid is found in the macrocyclic (36- or 72-membered) ring structures. These unusual lipids have been interested in connection with the physicochemical properties based on the lipid bilayer structure. Our interest in these lipids focuses on the biochemical significance of the macrocyclic molecular structures. Prerequisite is to develop synthetic methods of the macrocyclic lipids, because it is difficult to obtain significant amount of the archaeal lipids in pure form from natural sources.
We were the first in synthesizing the archae
al 36- and 72-membered macrocyclic lipids using McMurry coupling. In addition, a new and efficient approach to the macrocyclic lipids using olefin metathesis has been accomplished recently. In the presence of a Grubbs' ruthenium-alkylidene complex, RuCl_2(=CHPh)(PCy_3)_2, a ring closing metathesis (RCM) of α, ω-diene efficiently proceeded in 79% yield under high dilution conditions to give 36-membered lipid. By changing the reaction conditions, an acyclic diene metathesis (ADM) product was predominantly formed from the same substrate. The acyclic product was subsequently subjected to the RCM reaction under high dilution conditions to provide 72-membered lipid in 46%. Thus, both 36- and 72- membered lipids can be obtained at will from the same starting material only by changing the order and conditions of the metathesis reaction.
The physicochemical features of the 36-membered macrocyclic phospholipid were investigated in comparison with the corresponding acyclic counterpart in terms of fluidity, thermostability and permeability of the liposomes. Thermal analyses and monolayer studies indicated that the 36-membered macrocyclic phospholipid can aggregate to more tightly packed structures than the corresponding acyclic counterpart due to its less motional freedom at the alkyl chain region.
Furthermore, we found that the macrocyclic structure contributed to the formation of thermally stable membrane. These tendencies appear to be related to the tolerance of thermophilic archaea Methanococcus jannaschii against high temperature. Less