AU721481B2 - Control of iridodial compositions - Google Patents

Description

1 CONTROL OF IRIDODIAL COMPOSITIONS FIELD OF INVENTION This invention relates to a method of controlling iridodial compositions.

This invention has particular but not exclusive application to a method of converting or rectifying mixtures of tautomeric forms of iridodial and the complexes formed therefrom into a pharmaceutically useful iridodial form, and reference will be made herein to such application. However, this invention is not limited to such application, and the method may be used in the recovery of purified iridodial from iridodial sources generally.

10 DESCRIPTION OF THE PRIOR ART Iridodial is an experimental antimalignant pharmaceutical reagent characterised by the spontaneous formation of three tautomers for each type of iridodial structure: stereoisomers or epimers. The actual mixtures formed are sensitive to the local chemical and physical environment surrounding the material, 15 and are particularly sensitive to exposure to water.

It is believed by some researchers in chemotherapy that iridodial is potentially S. an extremely powerful genetic repair and protective factor. Iridodial may be synthesised in accordance with the procedure set forth in Ritterscamp et al., Journal of Organic Chemistry, Vol. 49 No. 7 (6 April 1984). The authors contended that synthetic iridodial showed a tendency to polymerise as evidenced by thickening on standing and that the monomer could be recovered by distillation.

Iridodial may also be obtained from the Australian meat ant, Iridomyrmex purpureus. Extraction of iridomyrmex ants gives very small yields.

SThe pyranol form of iridodial has been given the Chemical Abstracts Registry S 25 Number RN 69252-84-2, and the systematic name: [1R-(4a, 4aa, 7aa)]- 2 1,4,5,6, 7 7 a-hexahydro-4,7-dimethyl-cyclopenta[c]-pyran-1-ol. The dialdehyde structure with which it is tautomeric is known as alpha (2-formyl-3-methylcyclopentyl) propional. The term pyranol form has also been called enol acetal, enol hemiacetal or lactol at various times for the same structure. In this specification, the term pyranol is used to describe enolhemiacetal form. There are two pyranol forms continuously interchanging with each other and with the dialdehyde. The pyranol tautomers do contain an enolhemiacetal grouping and a hydrophilic hydroxyl group causing powerful intermolecular associations.

Tautomerism has been shown to be quite rapid at 20°C as shown by reaching 10 a substantially constant optical rotation in a few minutes in dilute solution in inert solvents but tautomeric equilibrium in concentrated form takes many hours and even days as self-escalating hydrophilic structures form. It has been discovered by the inventor that they avidly absorb atmospheric moisture to further increase in viscosity.

Iridodial gives a quantitative precipitation of iridodial bis(2,4-dinitrophenyl) hydrazone in a few minutes with 2,4-dinitrophenylhydrazine reagent. All the pyranol groups must be free to tautomerise to allow reaction as a dialdehyde. As there is only one dialdehyde tautomer, reaction with a reagent which reacts only with aldehyde groups must give a bis-derivative in 100% yield. Both the initially unreactive pyranol groups do tautomerise to the dialdehyde at a certain rate and give a complete conversion.

(Ford, Ph.D thesis, UNSW, 1958).

This establishes that there are no stable polymers present to tie up the dialdehyde. Complex formation in particular iridodial compositions could account for apparent irreproducibility of medical effects when the compositions are used.

It is postulated by the present applicant that there is a tendency for the less p ar dialdehyde tautomer to become enriched in the vapour phase. On condensing

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some tautomerism soon occurs and the hydrophilic pyranols soon dominate since they are strongly interactive, thus causing an escalating viscosity increase. They become too viscous for measuring out. Redistillation gives only a short respite and later uptake of trace atmospheric water is difficult to prevent and then greatly increases viscosity.

The foregoing proposition as explanation of viscosity increase in aged iridodial compositions is contrary to the earlier proposition of polymerisation which was put forward due to the degree of increase in viscosity, depolymerisation being also put forward as the mechanism of distillation. The recognition of this property provides for 10 admission of revised methods of handling iridodial compositions to enhance the presence of useful tautomers therein.

S SUMMARY OF THE INVENTION With the foregoing in view, this invention resides broadly in a method of controlling the composition of an iridodial mixture including the steps of: 15 heating a mixture containing iridodial to produce a vapour; and condensing the vapour in the presence of water vapour or ice crystals at a condensation temperature below -10°C to provide a pyranol-enriched iridodial/ice composition.

It has been surprisingly determined that the ice/pyranol complexes produced by the method of the present invention are stable on storage at reduced temperatures, and on melting are useful as experimantal oral, topical, or pleural iridodial pharmaceuticals.

The distillation may be a vacuum distillation procedure or an atmospheric- ;jR ressure process. For example, the pressure of the distillation may be a vacuum 25 pro ss at a pressure as low as 0.5 mm Hg and preferably 1 to 2 mm Hg, at a temperature as low as 900C and preferably above 1200C. atmospheric pressure distillation may be done to 2000C and preferably between 1200C and 1800C. The condensation temperature may be any sub -10°C temperature, for example, the convenient domestic freezer temperature of -40'C, or, for air transport, the temperature of solid carbon dioxide below In another aspect, this invention resides broadly in a method of converting a mixture of iridodial complexes into a reproducible, purified iridodial composition including the steps of distilling an iridodial source at a distillation temperature of between 900C and 2000C and a pressure of from 0.5 mm Hg to atmospheric in the presence of a substantially inert sweep gas; condensing the distillate vapour at a condensation temperature below -100C onto ice crystals to provide a solid composition, and maintaining the solid distillate at a storage temperature of below -100C and preferably at-40 9

C.

The sweep gas may be air, carbon dioxide or any inert gas. The sweep gas may include water vapour. The water content of the sweep gas may be controlled by providing a steam or water vapour source, such as, for example, gas heated boiling water bath steam. The sweep gas may be sucked into vacuum apparatus through a capillary tube to the bottom of the apparatus. It is preferred that the sweep gas is, or contains at least 10% water vapour.

The ice crystals may be resident in the condenser. The condenser-resident ice crystals may take the form of a relatively large mass of "snow", preferably a synthetic snow, preferably at a temperature of about -40°C. The snow is preferably pathogen and pyrogen free. The iridodial/ice product is preferably stored between C and -40 0

C.

Compositions in accordance with the foregoing, by control of tautomerism, optimise iridodial compositions for medical use. In particular the high pyranol product deposited on snow, a strongly, interactively hydrophilic surface, may be kept for a long time, ready for easy preparation of small dilute doses by melting in a few seconds to a high pyranol form product.

In a further aspect this invention resides in a method of storing freshly distilled iridodial tautomer mixtures at room temperature, the method including placing the mixture in a desiccator containing a desiccant selected to be substantially unreactive with iridodial vapour. Preferably, the desiccant is silica gel. Most conventional desiccants are unsuitable due to high reactivity such as sulphuric acid, phosphorus pentoxide and caustic potash, or calcium chloride.

Control of access to atmospheric water does not of itself prevent the iridodial i go,- 15 compositions from stiffening. However, it has been surprisingly determined that compositions that have become too viscous for use may be reconditioned using microwave energy.

Accordingly, in a yet further aspect, this invention resides broadly in a method of reconditioning viscous iridodial compositions that have been stored under desiccating conditions, the method including subjecting the composition to microwave energy in a microwave oven in the absence of moisture. Preferably, the microwave oven is a domestic unit operated at low power. Preferably, the microwave energy is applied in pulses, with testing of viscosity between pulses, the composition being considered ready for use when there is no change of viscosity between cycles.

he lvRA m c 21-p he less stiff, high pyranol product will revert on standing for about 12 hours, but may

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ee 6 be further reconditioned by the foregoing process. The viscosity drop on microwaving cannot fall to the temporary low level of distillation which can give high dialdehyde, low hydrophilic initial product.

In another aspect, this invention resides broadly in a reproducible mix of tautomers of iridodial when produced by any one of the methods herein defined.

It is believed that the reproducible mix may be stored for extended periods if cooled to, and stored at, the temperature of liquid nitrogen.

Tautomerisation begins immediately if the solid distillate begins to melt near 100C with the result that it cannot be re-solidified at -10OC. Freshly melted iridodial 10 redistills at 900C to 920C at 1 mm Hg pressure and is largely the dialdehyde form.

Accordingly, the iridodial may be reformed into the reproducible mix by the methods of the present invention.

In order that this invention may be more readily understood and put into

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practical effect, reference will now be made to the following examples which describe 15 preferred embodiments of the invention.

o*oo EXAMPLE 1 Og freshly distilled low viscosity iridodial was divided into 2x5g lots in two small test tubes. One was set aside at room temperature, as a control with a rubber stopper, and a glass rod inserted through the stopper so that it could slide.

The other was put into a larger stoppered tube acting as a small desiccator in which the desiccant was the commercial small-pored dried silica desiccant used to remove traces of water from the Freon gas in most modern refrigerators. The rubber stopper of the desiccant tube was fitted with a glass rod, sliding through the sealing port so that the iridodial within could be tested by prodding without moisture ingress.

On standing 24 hours the viscosity of both was so high that the tube and contents could be lifted by raising the rod, but the tube having access to trapped moisture, that is, no desiccant, had a definitely more viscous surface. The surface effect of atmospheric moisture became more pronounced as the exposure time increased.

The tube with desiccant was then submitted to low power kitchen microwaves for short periods of about 30 to 40 seconds and prodded to assess viscosity. The viscosity fell but not quite to the original level as could best be judged. The procedure could be repeated daily with no detectable change of viscosity whereas 10 the other control tube gradually got stiffer as water presumably mixed in during viscosity testing.

EXAMPLE 2 A cylindrical vessel 30cm long and lcm diameter was fitted with end plates and a close fitting helical stirrer, and an inlet and an end outlet. Into the cooled C..o 15 degrees C) vessel was placed 1kg synthetic snow precooled to -40 degrees C and stirring begun. The inlet port was fed a mixture of moist air and iridodial vapour and the outlet attached to a slow suction pump so that about 100ml/min of air containing iridodial passed through. 1 g iridodial was slowly evaporated into the inlet air by passing through a gently heated flask containing the iridodial. By experiment and observation it was relatively simple to evaporate the iridodial to get a relatively uniform co-crystallisation of the pyranol forms onto the snow surface lattice. The procedure was aided by the strong attachment of the hydrophilic pyranol groups to the highly polar hydrophilic snow surface. The pyranol I snow co-crystal was very stable at -40 degrees C and was well suited to storage.

EXAMPLE 3 Production of natural iridodial from iridomyrmex purpureus ants Dried ants contain 6-methylhept-5-ene-2-one alarm substance and a mixture of two major iridodials (cis-trans- and trans-cis-) together with many other minor compounds of differing volatility. The dried ants are macerated and columnextracted with BP Spiritus Vini Rectificatus. The filtered extract is a mix of residual volatiles plus sugars and unexamined fats and waxes as well as ant body water in alcohol. The extract was depleted of some water and alcohol be the addition of toluene followed by heating to azeotrope over the water and alcohol whilst retaining 10 the iridodial, allowing the simple decanter to work. The dry still residue yields the iridodials on fractional vacuum distillation as follows.

PREPARATION OF AN IRIDODIAL/ICE CONDENSATE A 500 ml 3-necked round-bottom flask had a controllable gas inlet connected to a source of steam in air. The middle neck had a thermometer and the third led to 15 a dry ice-cooled tube condenser, fitted with a stainless hand-operated scraper operating through a flexible rubber seal and also fitted at the end with a T piece connected to a vacuum pump.

Mixed epimeric iridodials from the previous crude extraction process was put in the flask and the iridodial residue was boiled by a mantle while the vacuum was adjusted to 2 mm Hg as the gas inlet was cracked open. Ice began to form in the condenser. Mantle heating visibly boiled the iridodial which mixed with the steam and was carried into the condenser. Scraping in the condenser gave brief glimpses of condensation too close to the inlet but also forming on the pre-formed material. The ccumulated ice/iridodial complex was removed from the condenser and stored at S25RAz2 25 2 O -o

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In use, the method of the present invention may be carried out with simple and compact equipment.

The purified iridodial/ice compositions of the present invention may be prepared for use by any melting means. Preferably, the compositions are melted by microwave energy for immediate use.

It is to be appreciated that the above has been given only by way of illustrative examples of the invention and that all such modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as claimed in the following claims.

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Claims (4)

1. A method of controlling the composition of an iridodial mixture including the steps of: heating a mixture containing iridodial to produce a vapour; and condensing the vapour in the presence of water vapour or ice crystals at a condensation temperature below -10oC to provide a pyranol-enriched iridodial/ice composition.

2. A method of converting a mixture of iridodial complexes into a C 10 reproducible, purified iridodial composition including the steps of: distilling an iridodial source at a distillation temperature of between 90°C and 200°C and a pressure of from 0.5 mm Hg to atmospheric in the presence of a substantially inert sweep gas; condensing the distillate vapour at a condensation temperature below 15 onto ice crystals to provide a solid composition, and maintaining the solid distillate at a storage temperature of below -1 OC.

3. The method of claim 1 or claim 2 in which the distillation temperature is between 120°C and 1800C.

4. A reproducible purified iridodial composition when produced by the method of any one of claims 1 and 2. DATED THIS EIGHTH DAY OF MAY, 2000 DOUGLAS LYONS FORD -BY PIZ EYS PATENT AND TRADE MARK ATTORNEYS w0