Tsuneo Ishiguro

Asymmetric total synthesis of natural (-)-and unnatural (+)-steganacin : Determination of the absolute configuration of natural antitumor steganacin

Abstract A virtually complete asymmetric control in the synthesis of 2,3-disubstituted butan-4-olide (10) was demonstrated by employing the butenolide (12) as the chiral acceptor for the conjugate 1,4-addition. Highly efficient asymmetric total synthesis of natural (-)- and unnatural (+)-steganacin was accomplished. The absolute stereostructure of natural antitumor steganain was determined to be 1.

First asymmetric total synthesis of (+)-steganacin determination of absolute stereochemistry

Abstract (+)-Steganacin was synthesized in a new and highly specific asymmetric pathway based on the novel application of chiral γ-lactone as a chiral synthon. By this synthesis the absolute stereochemistry of natural (−)-steganacin could be determined in unequivocal way.

Asymmetric total synthesis of the antileukaemic lignans (+)-trans-burseran and (–)-isostegane

(–)-Isostegane and (+)-trans-burseran were synthesized by a highly specific asymmetric pathway from a chiral butenolide.

Urinary sodium pump inhibitor raises cytosolic free calcium concentration in rat aorta.

We were able to purify two distinct sodium pump inhibitors to homogeneity from human urine based on [3H]ouabain-displacing activity from intact human erythrocytes. The polar and less polar compounds were eluted off the C18 reverse-phase column with 18% and 31% acetonitrile, respectively. The polar compound cross-reacted very weakly with specific antidigoxin antibody and lacked a characteristic ultraviolet absorption peak between 190 and 300 nm. The less polar compound showed a prominent digoxinlike immunoreactivity and had an ultraviolet spectrum similar to that of digoxin. We examined the effects of these compounds on cytosolic free calcium concentration in cultured rat vascular smooth muscle cells (AlO cells) using the fluorescent calcium chelator fura-2. Only the polar ouabain-displacing compound caused a significant increase, from 108±7 to 162±8 nM (n = 6, p < 0.01), in cytosolic free calcium concentration in AlO cells. The rise in cytosolic free calcium concentration induced by the polar ouabaindisplacing compound tended to be slower in onset and more sustained than that induced by arginine vasopressin. In contrast, ouabain and bufalin had no appreciable effects on cytosolic free calcium concentration in AlO cells. These results suggest that the polar ouabain-displacing compound we isolated from human urine may possess a vasoactive property and may play an important role in the modulation of vascular tone.

The effects of urinary digitalislike factor on cultured vascular smooth muscle cells.

We attempted to purify a digitalislike factor from human urine. On the assumption that a natural ligand for the digitalis receptor should be searched for on the basis of the effects on intact cells, we used an inhibitory effect on the binding of [3H]ouabain to human erythrocytes to determine digitalislike activity. A highly polar [3H]ouabain displacing activity was obtained by a combination of chromatographic procedures including reverse-phase high performance liquid chromatography. Urine-derived pHJouabain displacing activity, a competitive inhibitor of ouabain binding to human erythrocytes, acted on human lymphocytes in a similar manner. The dose-response curve of this compound was parallel to that of ouabain. Urine-derived [3H]ouabain displacing activity significantly inhibited monensin-stimulated increase in ouabain-sensitive MRb uptake, a parameter of Na+, K+-adenosine triphosphatase (ATPase), by 95% (p < 0.01) in cultured vascular smooth muscle cells (A10 cells). Furthermore, this compound enhanced net 45Ca influx by 30% (p < 0.01) and reduced 45Ca efflux by 35% (p < 0.01) in A10 cells. These results suggest that urine-derived [3H]ouabain displacing activity may be a regulator of Na+, K+-ATPase and a modulator of vascular tone.

Effects of human urine-derived digitalis-like factor on cultured renal tubular epithelial cells.

We purified a polar digitalis-like factor to apparent homogeneity from human urine using inhibition of 3H-ouabain binding to intact human erythrocytes to monitor digitalis-like activity. Since endogenous digitalis-like factor may act as a natriuretic hormone, we tested the binding characteristics of this urine-derived ouabain-displacing compound to the sodium pump in intact renal epithelial cells, in order to assess its potential physiological significance. Cultured canine and porcine epithelial cell lines, MDCK and LLC-PK1, had a high sodium pump density as estimated from 3H-ouabain binding sites. Human urine-derived ouabain-displacing compound showed a dose-related inhibition of 3H-ouabain binding to both of these cells, similar to the inhibition of unlabelled ouabain. These findings indicate that the ouabain-displacing compound is capable of acting on the sodium pump in intact renal epithelial cells and may be the circulating regulator of Na+,K+-ATPase.