Synthesis and characterization of N-bromoacetyl-3,3',5-triiodo-L-thyronine

pH-zone-refining counter-current chromatography: origin, mechanism, procedure and applications

Since 1980, high-speed counter-current chromatography (HSCCC) has been used for separation and purification of natural and synthetic products in a standard elution mode. In 1991, a novel elution mode called pH-zone refining CCC was introduced from an incidental discovery that an organic acid in the sample solution formed the sharp peak of an acid analyte. The cause of this sharp peak formation was found to be bromoacetic acid present in the sample solution which formed a sharp trailing border to trap the acidic analyte. Further studies on the separation of DNP-amino acids with three spacer acids in the stationary phase revealed that increased sample size resulted in the formation of fused rectangular peaks, each preserving high purity and zone pH with sharp boundaries. The mechanism of this phenomenon was found to be the formation of a sharp trailing border of an acid (retainer) in the column which moves at a lower rate than that of the mobile phase. In order to facilitate the application of the method, a new method was devised using a set of retainer and eluter to form a sharp retainer rear border which moves through the column at a desired rate regardless of the composition of the two-phase solvent system. This was achieved by adding the retainer in the stationary phase and the eluter in the mobile phase at a given molar ratio. Using this new method the hydrodynamics of pH-zone-refining CCC was diagrammatically illustrated by three acidic samples. In this review paper, typical pH-zone-refining CCC separations were presented, including affinity separations with a ligand and a separation of a racemic mixture using a chiral selector in the stationary phase. Major characteristics of pH-zone-refining CCC over conventional HSCCC are as follows: the sample loading capacity is increased over 10 times; fractions are highly concentrated near saturation level; yield is improved by increasing the sample size; minute charged compounds are concentrated and detected at the peak boundaries; and elution peaks are monitored with a pH flow meter for compounds with no chromophore. Since 1994, over 70 research papers on pH-zone-refining CCC have been published with the trends increasing in the recent years.

pH-zone-refining countercurrent chromatography

A recently developed preparative technique, pH-zone-refining countercurrent chromatography (CCC), separates organic acids and bases according to their pKa and hydrophobicity. The hydrodynamic mechanism of pH-zone-refining CCC is illustrated in two elution modes along with a simple mathematical analysis. Separations include acidic and basic derivatives of amino acids and peptides, hydroxyxanthene dyes, alkaloids, indole auxins, and structural and geometrical isomers. In addition, recently developed affinity ligand separations of enantiomers, polar catecholamines, and free peptides are also described. Technical guidance is provided for interested users so that they can conduct a systematic search for the optimum solvent system and experimental conditions. Advantages as well as limitations of the present technique are discussed.

12-O-tetradecanoylphorbol 13-acetate and fibroblast growth factor increase the 30-kDa substrate binding subunit of type II deiodinase in astrocytes

Type II 5'-deiodinase (D-II) catalyzes the intracellular conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the brain. The D-II activity in astroglial cell cultures is induced by several pathways including cyclic AMP (cAMP), 12-O-tetradecanoylphorbol 13-acetate (TPA), and fibroblast growth factors (FGFs). We have examined the effect of TPA and FGFs on the 30-kDa substrate binding subunit of D-II, by affinity labeling with N-bromoacetyl-[125I]T4 in astroglial cells. TPA (0.1 microM), 20 ng/ml acidic FGF (aFGF), and 1 mM 8-bromo cyclic AMP all caused an increase in the 30-kDa protein. cAMP induced the greatest increase (fivefold) followed by TPA (3.2-fold) and FGF (2.8-fold). Glucocorticoids acted synergistically with cAMP and aFGF and promoted the effect of TPA. Affinity labeling was competitively inhibited by bromoacetyl-T4 > bromoacetyl-T3 > T4 > reverse T3 > iopanoic acid > T3 > 3,5,3'-triiodothyroacetic acid. The effect of TPA (0.1 microM) was maximum at 8 h and then gradually decreased. aFGF (20 ng/ml) plus heparin (17 micrograms/ml) induced a maximal 30-kDa increase at 8 h, which stayed stable for up to 24 h. The effect of aFGF was concentration dependent. Of the other growth factors studied, only basic FGF and platelet-derived growth factor induced small increases in the 30-kDa protein. Epidermal growth factor had little effect. In vitro labeling of cAMP, TPA, and aFGF-stimulated cell sonicates resulted in an increase in the 30-kDa protein that paralleled the increase in D-II activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on an abnormally sharpened elution peak observed in counter-current chromatography

Counter-current chromatography (CCC) of the bromoacetylation product of 3,3',5-triiodo-L-thyronine (T3) produced an unusually sharp peak for the desired product, N-bromoacetyl T3 (BrAcT3). A series of experiments revealed that bromoacetic acid, probably present as a side reaction product in the sample solution, was responsible. This compound repressed the ionization of the carboxyl group of BrAcT3 forcing it into the less polar stationary phase until the bromoacetic acid had eluted completely from the apparatus. At this point, the sudden increase of pH and consequent ionization of the BrAcT3 allowed the ammonium salt of the latter to enter the more polar moving phase where it eluted rapidly from the column as a sharp peak. The same phenomenon was observed in the CCC fractionation of a series of indole auxins where addition of trifluoroacetic acid to the sample caused peak sharpening by the same process. The phenomenon recalls pH gradient elution and isoelectric focussing except that the substance responsible for the pH range here is added along with the sample in one bolus forming a sharp pH gradient at its trailing edge. As with gradient elution, the technique is of practical interest since it permits collection of the eluting compounds with increased detectability in fewer fractions. The technique can also enhance separation of compounds whose partition coefficients differ with a change in pH.

Synthesis and properties of N-bromoacetyl-L-thyroxine

A one-step bromoacetylation of L-thyroxine (T4) produces N-bromoacetyl-L-thyroxine (BrAcT4) in good yield. The reaction product is best purified by high-speed countercurrent chromatography. While HPLC is satisfactory only for purification of microgram and submicrogram quantities, amounts ranging from about 1 ng to 1 g of BrAcT4 can be processed by high-speed countercurrent chromatography (HSCCC), a method which we have previously used for the purification of N-bromoacetyl-3,3',5-triiodo-L-thyronine (BrAcT3). Operating conditions for the one-step synthesis of BrAcT4 and BrAcT3 differ due to differences in solubility and reactivity of the two hormones. BrAcT4 purified by HSCCC and shown to be pure by analytical HPLC has been characterized by alpha max and epsilon max in the near and far uv in several solvents, mass spectrum, 1H NMR spectrum, TLC in three solvent systems, retention time in reverse-phase HPLC (C18) in relation to the retention times of two internal standards, 3,3',5-triiodo-L-thyronine and T4, and melting point. Corresponding data for BrAcT3, not previously reported, have also been determined. The described procedure can provide not only substantial amounts of highly purified BrAcT4 for competition studies, but also 125I-labeled BrAcT4 of high specific activity for affinity labeling. Since solutions of BrAcT4 and of BrAcT3 undergo partial decomposition on evaporation to dryness, suitable procedures for the preparation of these hormones in solid form and for storage in solutions have been devised.