Young-Sook Paik

Propionylshikonin from the roots ofLithospermum erythrorhizon

A shikonin derivative was isolated from the roots ofLithospermum erythrorhizon with silica gel column chromatography and preparative TLC. The structure of the isolated pigment was identified as propionylshikonin by NMR and mass spectrometric analysis. The isolation of propionylshiknin was for the first time in the nature.

Stability of carthamin fromCarthamus tinctorius in aqueous solution: pH and temperature effects

Thermal stability of a red pigment, carthamin, fromCarthamus tinctorius was investigated to explore possible applications as natural color additives for foods, cosmetics, and nutraceuticals. Degree of degradation reactions of carthamin at acidic, neutral and alkaline conditions were determined with UV/Vis spectral measurements. Decomposition half lives of carthamin at 25°C were 4.0 h, 5.1 h, and 12.5 h at pH 5.0, pH 7.0, and pH 12.0, respectively, indicating that carthamin is much more stable at alkaline pH than acidic or neutral conditions. The activation energies of carthamin at pH 5.0, pH 7.0, and pH 12.0 were 15.6, 15.7 and 16.8 kcal/mol, respectively.

Complex formation of tunichrome Mm-2 with ferrous and ferric ions

Mm-2, a tunichrome from iron-accumulating tunicate,Molgular manhattensis, was synthesized and measured by uv/visible spectrophotometer for the complex formation with iron. Several portions (0.1–0.5 equivalents) of freshly prepared degassed aqueous ferrous chloride solution were added to Mn-2 in 10 mM degassed sodium phosphate buffer, pH 7.0. Absorption maximum at 325 nm of Mm-2 was disappeared upon addition of ferrous chloride with concomitant appearance of absorption peaks at 365 nm and about 590 nm. Stoichiometry of Mm-2/iron complex was estimated as about 2.5∶1. The uv/visible spectrum of free Mm-2 in which hydroxyl groups were protected witht-butyldimethylsilyl (TBDMS) groups was not changed upon addition of ferrous chloride. This result suggests that catechol moieties of tunichrome Mm-2 play an important role for the complexation reaction. The addition of ferric chloride showed an essentially identical final absorption spectrum as in ferrous chloride case except that ferric chloride should be added in excess. These preliminary results support that tunichrome Mm-2 has an ability to chelate iron and to reduce Fe(III) to Fe(II).

Synthesis and evaluation of succinic acid derivatives as prolyl endopeptidase inhibitors

Many synthetic peptide-based prolyl endopeptidase (PEP) inhibitors are depended on the acy-l-L-prolyl-pyrrolidine structure. The pyrrolidine ring at P1 and a large variety of lipophilic acyl groups at P3 have been reported to be important for potent PEP inhibitory activity. Upon exploration of a new lead compound for PEP inhibition, succinic acid was introduced at the P2 position to replace the l-proline in acyl-l-prolyl-pyrrolidine. A series of amido-succinylpyrrolidine compounds (1–9) were synthesized, and their PEP inhibitory activities were evaluated. Of these, compound 9 showed the most potent PEP inhibitory activity with IC50 of 6.4±0.6 nM.