Amphiphilic Aspects and Micellar Structures of Anti-inflammatory Agents a -and $-Glycyrrhizinate Misao KoiDE1, Jinta UKAWA2, Akito ODAKA*1, Waichiro

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1 Amphiphilic Aspects and Micellar Structures of Anti-inflammatory Agents a -and $-Glycyrrhizinate Misao KoiDE*1, Jinta UKAWA*2, Akito ODAKA*1, Waichiro TAGAKI*2, and Seizo TAMAGAKI*2 Pharmaceutical Research Laboratories of Lion Corporation Department of Bioapplied Chemistry, Faculty of Engineering, Osaka City University Abstract : Micellar solutions of dipotassium /3- glycyrrhizinate (GK2) have been studied by measuring surface tension, solubilization, fluorescence, circular dichroism, and light-scattering. To better understand particularly the role played by the triterpenoidal carboxyl group of GK2, the physico-properties of its methyl ester derivative of glycyrrhizinate (GMe) have also been examined for comparison ; GK2 and GMe each forms a relatively small micelle with the aggregation number of 20 to 25 at ph 7.4 slightly above each cmc. An increasing ph makes the cmc values larger. At higher concentrations GK2 forms larger micelles with a core of alcohol-like polarity, while relatively more hydrophobic GMe forms cylindrical aggregates with a closed, dehydrated core. Meanwhile, the origin of the facile gelation of GK2 is implicated by Molecular Mechanics (MM) calculations. Furthermore, partitioning of the GK2 derivatives between the water and 1-octanol phases is examined at various phs in the absence and presence of phase transfer catalysts of various types. Some kinds of the cationic catalysts facilitated the water-to-1-octanol phase transfer of GK 2 and GMe even at ph 5 to 7. Key words : dipotassium,8-glycyrrhizinate, critical micelle concentration, micelle formation, drug carrier 29

2 Fig. 1 Plots of Surface Tension at ph 4.9 in 0.1 M Citrate Buffer vs. the Logarithms of GK 2 and GMe Concentrations.

3 Fig. 2 Plots of Amax and Absorbance vs. THF vol% in Aqueous THF. Table 1 cmc Values of GK 2 and GMe in 0.1 M Citrate Buffer (ph 4.9). a) Not determined.

4 Fig. 3 Debye Plots of a -and 1e-GK2 Derivatives. K : constant, Rgo : scattering intensity, C : [GK2] or [GMe]-cmc Fig. 4 Plots of Absorbance at 410 nm vs. GK 2 or GMe Concentration and Amax vs. GMe Concentration. Table 2 Micellar Weight, Aggregation Number, Size and Shape of a -and B-GK 2 Derivatives a). a) Measured by DLS and SLS at cmcs.

5 Fig. 5 Variation of Observed 340 nm CD Intensity (a, b : GK2, c, d : GMe) as a Function of GK2 and GMe Concentrations. a, c : ph 7.4, 0.1 M phosphate buffer ; b, d : ph 4.9, 0.1 M citrate buffer. Fig. 6 Over-simplified Pictures of Micellar Structures' of GK2 and GMe at a Neutral ph.

7 Table 3 Molecular Mechanics Stabilization Energies of a-and 13-GK2. HB : intramolecular hydrogen-bonding. MM : Molecular mechanics. Fig. 7 ph Dependency of % GK2 and GMe Transferred from the Water Layer to 1-Octanol Layer. 1 : TBAP, 2 : DABCO2+, 3 : DSAC, 4 : STAC, 5 : 18-crown 6-ether

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