WO1991006547A1

WO1991006547A1 - Indolizidine alkaloids

Info

Publication number: WO1991006547A1
Application number: PCT/GB1990/001655
Authority: WO
Inventors: Haldane Alexander Pontoppidan Broby
Original assignee: Novalal Plc
Priority date: 1989-10-27
Filing date: 1990-10-29
Publication date: 1991-05-16
Also published as: AU6630790A; GB8924292D0

Abstract

Alkaloid dimers formed by reacting either Castanospermine or Swainsomine with a compound of formula (1) in the presence of beta cyclo-dextrin glucosyl transferase. The novel dimers are useful as antiviral agents. Pharmaceutical compositions containing alkaloid dimers are also enclosed.

Description

Indolizidine alkaloids.

This invention relates to novel alkaloids, in particular novel alkaloid dimers and to a novel method of polymerising alkaloids to produce the dimers.

Indolizidine alkaloids such as Castanospermine (CTS) (1,6,7,8 - tetrahydrcxyoctahydroindolizidine), deoxynojiromycin (DNJ) and 2, 5 - dihydroxymethyl-3, 4,

d ihydroxypyrolod ine (DMDP) have been shown to exhibit anti-viral and anti-retro-viral activity (P.S.

Sankara et al, 1987., A.S. Tyms et al, 1987).

These compounds have been shown to be inhibitors of glucosidase synthesis. Glucosidases are important for viruses to "dock" onto the cells which they attack, thus inhibition of the synthesis of such enzymes by the virus prevents it attacking healthy cells.

Castanospermine shows promising potential as an antiviral agent with possible application in the treatment of AIDS. Other indolizidine alkaloids have been shown to have antiviral activity and may be potentially useful in the treatment of diabetes, cancer as well as AIDS.

It has now been found that, by polymerising

Castanospermine or Swainsomine with other

indoliz idine alkaloids, novel sterospecific

indolizidine alkaloid dimers can be produced which have significant synergistically enhanced ant iviral properties .

According to one aspect of the invention there is provided an alkaloid dimer formed by

reacting either Castanospermine, which has the formula

or Swainsomine, which has the formula

with a compound of formula (1)

wherein R¹ and R² are different and are either H or OH, and R³ is either H or CH₂OH, in the

presence of beta cyclo-dextrin glucosyl transferase.

The group of compounds defined by formula (1) embraces such compounds as deoxynojirimycin (DNJ), which has the formula,

deoxymannojirimycin (DMJ), which has the formula,

and homonojirimycin, which has the formula

Thus the alkaloid dimers that can be formed using beta-cyclo dextrin glucosyl transferase include

Castanospermine - DNJ, Swainsomine - DMJ,

Castanospermine - DMJ and Swainsomine - DNJ.

The novel alkaloid dimers defined above can be prepared by mixing Castanospermine or Swainsomine with another indolizidine alkaloid having a six- membered ring structure, such as deoxyncjirimycin, deoxymannojirimycin, homonojirimycin in the presence of beta cyclo-dextrin glucosyl transferase.

According to a second aspect of the invention there is provided a method of preparing an alkaloid dimer as defined above comprising reacting either Castanospermine or Swainsomine with a compound of formula (1), as hereinbefore defined, in the presence of beta cyclo-dextrin glucosyl transerase.

The starting materials for the preparation of these novel alkaloid dimers can generally be prepared by extracting them from plant material . Thus for example Castanospermine can be extracted from the chestnut-like seeds of an Australian tree called the Moreton Bay Chestnut, or Castanospermum australe. DNJ can be found in the mulberry, but it can also be prepared by chemically modifying nojirmycin, which has been found to occur in a species of Streptomyces. Swainsomine can be

extracted from a small pea-like plant of the genus Swainsona, which is found in Western Australia, as well as other pea-like plants, Astragalus and

Oxytropis, found in the United States.

In order to prepare and separate the relevant alkaloid, ammonina is added to an aqueous extract of the relevant plant. The alkaloid is then separated by shaking the extract with a solvent such as chloroform. On standing the mixture separates into two layers, water and chloroform, with the alkaloid in the water layer. The desired compound may then be isolated using such methods as ion- exchange chromatography using beads of sulphonated polystyrene modified so that they can bind alkaloids and remove them from solution. The bound alkaloids may then be released using dilute ammonia.

Alternatively the alkaloids may be prepared from plant cell suspension cultures using continuous fermentation. Thus if a suspension of alkaloid producing plant cells is introduced into a liquid nutrient medium and allowed to incubate for a period of time, the plant cells will produce the alkaloid, either intracellularly or extracellularly, which can then be harvested by an appropriate method.

In order to prepare the dimers of the present invention, an aqueous solution of

Castanospermine or Swainsomine is added to an aqueous solution of alkaloid of formula 1, for example DNJ or DMJ, and to this is added the beta cyclo-dextrin glucosyl transferase enzyme, and then incubated at 37ºC.

According to a further aspect of the invention there is provided a pharmaceutical composition comprising an alkaloid dimer as

hereinbefore defined in combination with a

pharmaceutically acceptable carrier.

Such compositions may be administered orally, parenterally or nasally and so may take the form of tablets, suspensions for oral or intravenous administration, or aerosols.

This invention will now be further described by way of reference to the following examples.

Example 1

1 mg of deoxynojirimycin was dissolved in (18 2 MSL reverse osmosis) water to give a 1 %

solution. To this was added a 10% solution of

Castanospermine prepared by dissolving 1 mg of it in (18 2 MSL reverse osmosis) water. To this was added beta cyclo-dextrin glucosyl transferase at 10 units of activity (as measured by paramitrophenol

liberation at 410 nm), which was then incubated at 37°C.

0.2 mg of DNJ - Castanospermine dimer was produced. The product was verified using

L-Glucosidase inhibition, and Pulsed Amperometric detection EPIC using CG3 and C53 columns on a Dionex Pad HPLC system.

Example 2

Using the method described in Example 1 the following dimers were made:- DMJ - Swainsomine

DMJ - Castanospermine

DNJ - Swainsomine

Claims

1. An alkaloid dimer formed by reacting either Castanospermine having the formula

or Swainsomine having the formula

with a compound of formula (1)

wherein R ¹ and R² are different and are either H or OH, and R³ is either H or CH₂OH, in the

presence of beta cyclo-dextrin glucosyl transferase.

2. An alkaloid dimer as claimed in Claim 1 which is formed by reacting Castanospermine with either deoxyno j ir imycin or deoxymannojirimycin.

3. An alkaloid dimer as claimed in Claim 1 which is formed by reacting Swainsomine with either aeoxynoj irimycin or deoxymannojirimycin.

4. A method for preparing an alkaloid dimer as claimed in any one of Claims 1 to 3 comprising polymerising Castanospermine or Swainsomine with a a compound of formula ( 1 ) .

presence of beta cyclo-dextrin glucosyl transferase.

5. A method according to Claim 4 comprising reacting Castanospermine with either deoxynojirimycin or deoxymannojirimycin.

6. A method according to Claim 4 comprising reacting Swainsomine with either deoxynojirimycin or deoxymannojirimycin.

7. A method according to any one of Claims 4 to 6 wherein the Castanospermine, Swainsomine and compounds of formula (1) are prepared by extraction from alkaloid containing plant material.

8. A pharmaceutical composition comprising an alkaloid dimer as claimed in any one of Claims 1 to 3 in combination with a pharamceutically acceptable carrier.