WO1997019099A1

WO1997019099A1 - Positive inotropic ouabain stereoisomer

Info

Publication number: WO1997019099A1
Application number: PCT/US1996/018847
Authority: WO
Inventors: Darko Kantoci
Original assignee: Loma Linda University Medical Center
Priority date: 1995-11-22
Filing date: 1996-11-22
Publication date: 1997-05-29
Also published as: AU1123197A

Abstract

A positive inotropic ouabain stereoisomer having structure (I).

Description

POSITIVE INOTROPIC OUABAIN STEREOISOMER

Field of the Invention

The present invention relates to a ouabain stereoisomer derivative that is useful as a positive inotropic agent.

Background of the Invention

Experimental evidence has confirmed the existence of an endogenous digitalis-like Na"7K^* -ATPase inhibitor, structurally similar to the plant-derived glycoside ouabain, in mammals. This compound, variously denoted hypothalamic Na,K-ATPase inhibitory factor (HIF), ouabain-like compound (OLC), and endogenous digftalisiike factor (EDLF), has been isolated from bovine hypothalamus and human plasma. The compounds so isolated have been shown to be identical to each other, but different from ouabain. See, e.g. , Zhao et al., Biochemistry, vol 34, pp. 9893-96 (1995); Tymiak et al. , Proc. Natl. Acad. Sci. USA, vol 90, pp. 8189-93 (Sept. 1993); Mathews et al. , Hypertension, vol. 1 7, No. 6, Part 2, pp. 930-35 (June 1991 ). The structure of HIF/OLC has been found to be an isomer of ouabain. However, the precise structure of HIF/OLC has proven elusive.

Summary of the Preferred Embodiments

In accordance with one aspect of the present invention, there is provided a ouabain stereoisomer having the following structure:

In accordance with another aspect of the present invention, there is provided a method for increasing heart contractility in a mammal which comprises the step of administering to the mammal a therepeuticaliy effective amount of the foregoing ouabain stereoisomer.

Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.

Brief Description of the Drawings

The invention may be more readily understood by referring to the accompanying drawings in which

Figs. 1 -2 are CD spectra (in acetonitrile) of the pentanaphthoate of the inventive ouabain stereoisomer (HIF/OLC) and of 1 , 19,2',3',4'-ouabain pentanaphthoate, respectively.

Detailed Description of the Preferred Embodiments

The precise structure of HIF/OLC has now been determined. The compound has the IUPAC designation 3/?-[(6-deoxy-σ-L-mannopyranosyl)oxy]- 1 σ,50,1 1 σ, 140,1 9£-pentahydroxycard-20(22)-enolide, and has the following structure:

The compound differs from ouabain in the stereochemistry of the hydroxyl group at the 1 -position.

Isolation of HIF/OLC has been succinctly described, e.g., in Zhao et a/. , p. 9894, cited above, which summarized previous work and which is incorporated herein in its entirety by reference. Briefly, HIF is obtained from a methanol/water extract of bovine brain tissue maintained at low temperature (-80 °C) from the time the sample is gathered until the time of analysis. The extract is delipidated through petroleum ether and chloroform extraction followed by lipophilic gel chromatography in methanol, ion-exchange chromatography, and additional concentration using CHP20P resin (MCI gel, Mitsubishi Chemical, Tokyo, Japan). Next, additional affinity purification is carried out using SDS-extracted canine kidney Na,K-ATPase which is coupled to paramagnetic iron particles (Bio Mag 4100, Advanced Magnetics, Cambridge MA) by cross linking of primary amino groups using glutaraldehyde. The affinity-purified HIF is then concentrated with reversed-phase C,_β HPLC. A linear gradient of acetonitrile/water is used in the HPLC step. Isolation of OLC is also described in Zhao et al.

The compound so isolated is next naphthoylated according to methods well known to those skilled in the art, for example, as described in Zhao et al. , to produce HIF pentanaphthoate. 1 , 1 9,2',3',4'-Ouabain pentanaphthoate is prepared in a similar manner. This latter compound has the following structure: •

CD (circular dichroic) spectra of HIF pentanaphthoate and the corresponding 1 ,1 9,2',3',4'-ouabain pentanaphthoate, in acetonitrile, are obtained and compared (Figs. 1 -2). The CD curve of ouabain pentanaphthoate in Fig. 1 shows a split curve with a strong Cotton effect, indicative of exciton coupling among the naphthoate groups. The Cotton effect is influenced by the three-dimensional positioning of the naphthoate groups.

In contrast, the CD curve for HIF pentanaphthoate in Fig. 2 shows no such split and substantially no Cotton effect. Changing the orientation of the hydroxyl group at the 1 position in ouabain results in a change in the position of the chromophore (i.e., the naphthoyl group) upon naphthoylation, which results in suppression of the Cotton effect as shown in Fig. 2. This demonstrates that HIF pentanaphthoate has the following structure:

This establishes the structure of HIF/OLC. The inventive compound is a positive inotropic agent, that is, an agent that increases the contractility of the heart. Thus, the compound of the invention can be used to treat cardiac failure to slow ventricular rate in the presence of fibrillation and flutter by increasing the force of myocardial contraction. Compared to either itself or digoxin, which is conventionally used in patients in need of such treatment, the inventive compound is more potent than either and has an improved therapeutic ratio where toxicity is associated with induced arrhythmias.

Effective amounts of the inventive compound range from about 5 μg to 1000 μg, more preferably about 10 μg to 100 μg. The compound preferably is administered orally in solid or liquid form. Suitable forms of administration which are readily produced according to methods known to those skilled in the art and include capsules, tablets, dispersible powders, granules, syrups, elixirs and suspensions. These compositions can contain one or more conventional adjuvants, such as sweetening agents, flavoring agents, coloring agents and preserving agents.

Tablets can contain the inventive compound in a mixture with conventional pharmaceutically acceptable excipients. These include inert carriers, such as calcium carbonate, sodium carbonate, lactose, and talc; granulating and disintegrating agents, such as starch and alginic acid; binding agents such as starch, gelatin acacia; and lubricating agents, such as magnesium stearate, stearic acid and talc. Tablets may be uncoated or coated by known techniques to delay disintegration and absorption in the gastrointestinal tract thereby providing a sustained action over a longer period of time. Capsules may contain the inventive compound in admixture with an inert solid carrier, such as calcium carbonate, calcium phosphate or kaolin. Similarly, suspensions, syrups and elixirs may contain the inventive compound in mixture with any of the conventional excipients utilized in the preparation of such compositions. This includes suspending agents such as methylcellulose, tragacanth and sodium alginate; wetting agents such as lecithin, polyoxyethylene stearate or polyoxyethylene sorbidan monoleate; and preservatives.

Claims

What is claimed is:

1 . A ouabain stereoisomer having the following structure:

2. A method for increasing myocardial contractility in a mammal which comprises the step of administering to said mammal a therepeuticaliy effective amount of the ouabain stereoisomer of claim 1 .

3. A method for the treatment of cardiac failure in a mammal which comprises the step of administering to said mammal a therepeuticaliy effective amount of the ouabain stereoisomer of claim 1 .

4. The method of claim 3 wherein said mammal is a human.

5. The method of claim 4 wherein said amount ranges from about 5 μg to 1000 g.

6. The method of claim 6 wherein said amount ranges from about 1 0 μg to 100 μg.

7. The method of claim 4 wherein said compound is administered orally in solid or liquid form.