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ECM 20 （Krakow, Poland） Diversity of Host Framework of Bile Acids with Different Side Chain Lengths Kazuaki Kato, Michihiro Sugahara, Kazuki Sada and Mikiji Miyata Material and Life Science, Graduate School of Engineering, Osaka University 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan |
We study on crystal structures of bile acids. Some of
bile acids have a variety of host frameworks to include various guest compounds. Cholic
acid, one of the most well known host compound, have been revealed to have at least nine
different host frameworks.1 Recently, we found that these frameworks were
alterable according the side chain lengths Nordeoxycholic acid (NDCA) has a side chain
which is one methylene group shorter than deoxycholic acid. We found that NDCA formed
quite different host framework from deoxycholic acid.2 It indicates that the
difference of one methylene group in side chain should be enough to change the host
framework. We present here the diversity of the host framework of bile acids with
different side chain lengths.
We prepared five cholic acid derivatives with 0-4 methylene
groups in side chain. Each of the derivatives with 0,1 and 2 methylene groups form quite
different host frameworks and hydrogen bonding modes. Moreover, the diversity of host
framework causes the different inclusion ability. The derivatives with 1 and 2 methylene
groups form inclusion crystals with various guest compounds while the derivative with 0
methylene group forms only the guest-free crystal.
On the other hand, each of the derivatives with 2,3 and 4
methylene groups form the same hydrogen bonding mode due to the unaltered bonding. The
identical host framework is observed in the derivatives with 2 and 4 methylene groups.
Since this framework is robust against the elongation of the side chain, the controlled
expansion of a molecular cavity is effected.3
Another bile acid also shows the diversity of host framework.
Many derivatives with different side chain length have been synthesized from various bile
acids. In every bile acid, the differences of side chain lengths cause the alterations of
host frameworks with the variety of hydrogen bonding modes. Because the numbers and
positions are different in each acid, the various effects of side chain length are
observed.
As described above, diversity of host framework is mainly
caused by the changes of hydrogen bonding modes. These modes are alterable not only by the positions of polar groups but also
by the lengths of methylene side chain.
[1]
Mikiji Miyata, et al. in Comprehensive Supramolecular Chemistry, Vol. 6, (Eds: J.
L. Atwood, et al.) Pergamon, New York, (1996): pp.147-176
[2] Kazuki Sada, et al. "First Columnar Molecular Structure of
Bile Acids Inclusion Crystal.", Chem.
Lett., (1998): 31-32.
[3] Kazuki
Sada, et al."Controlled Expansion of a Molecular
Cavity in a Steroid Host Compound.", J.Amer.Chem.Soc.,
123(19), 4386-4392, 2001