WO1992008352A1

WO1992008352A1 - Avermectins and milbemycins to treat parasitic infestations in fish

Info

Publication number: WO1992008352A1
Application number: PCT/GB1991/001979
Authority: WO
Inventors: Cyril Keith Milner
Original assignee: Beecham Group Plc
Priority date: 1990-11-16
Filing date: 1991-11-11
Publication date: 1992-05-29
Also published as: GB9024928D0; ZA919024B; AU8877691A; IE913972A1

Abstract

Avermectins and milbemycins are useful in the treatment of endo- and ectoparasitic infestations in fish.

Description

Avermectins and mi ^"I b envy c ins to treat parasiti c infestations in fish .

This invention relates to a method of treating parasites in fish.

This invention is particularly concerned with the use of certain avermectins and milbemycins described in EP-A-0 421 568 (USSN 525,094) for the treatment or prophylaxis of endo- and ectoparasitic infestations of fish, especially fin-fish such as salmon, trout, carp, cat fish and yellow tail.

The compounds used in this invention have parasiticidal properties, for example against nematodes, and are useful for the treatment of helminthiasis.

The term helminthiasis encompasses diseases caused by infestation with parasitic worms such as Strongyles, Ascarids, hookworms, lungworms, filarial worms and whipworms.

The compounds used in this invention are also active against Arthropods. The phylum Arthropoda comprises insects - such as biting flies, lice, bugs, beetles and fleas - and arachnids - such as mites and ticks.

Thus the present invention provides the use of a compound of general formula (I) as defined below for the manufacture of a medicament for the treatment or prophylaxis of endo and ectoparasitic infestations, in fish.

The present invention also provides a method of treatment or prophylaxis of endo- and ectoparasitic infestations, which comprises administering an effective non-toxic amount of a compound of general formula (I) as defined below to a fish in need thereof. This invention is particularly concerned with the treatment of infestations of parasitic copepods or sea-lice, for example Lepeophtheirus and Caligus, in fish subject to such infestations, especially salmonids.

For use according to the invention the compounds of general formula (I) may be formulated for administration with carriers and adjuvants in any convenient way for use in veterinary medicine, by analogy with known anthelmintics.

The compounds of general formula (I) may be administered orally, for example as a paste, tablet or capsule, but typically as a food additive, for example granules, pellets or powder, which are blended with the feed. The compounds may also be administered topically, for example in sprays or baths, typically by dipping or holding the fish in a solution or suspension of the compound, or by addition of the compound to a stock pool or holding tank. Additionally, the compounds may be administered by injection or intubation.

The compounds of general formula (I) may be formulated as a mixture with each other and/or with other anthelmintics, insecticides, acaricides or other pharmacologically active substances.

Suitably the composition consists of sufficient material to provide a dose of from 0.001 to lOOmg of active ingredient per kg of fish body weight per dose, more suitably 0.01 to lOmg/kg per dose.

A composition for use in the invention may suitably contain from 0.1% by weight, preferably from 1.0 to 60% by weight, of the compound of general formula (I) (based on the total weight of the composition) , depending on the method of administration. It will be appreciated that, in some cases, it will be advisable to repeat the dosing of the infected or potentially infected fish with the compound of general formula (I) according to conventional dosage regimes ysed with anthelmintics:

The compound used in this invention is an avermectin or milbemycin selected from avermectins and milbemycins having the general formula (I) :

(I)

wherein R1 is hydrogen or optionally protected hydroxy; R_? is alkoxy, optionally protected hydroxy, oxo or optronally O-substituted oximino; r is hydrogen, optionally protected hydroxy,or a group 4'- (α-L-oleandrosyl)-α-L-oleandrosyloxy or α-L- oleandrosyloxy wherein the terminal hydroxy group is optionally protected; R , R , R and R are the same or o different and each is hydrogen or an organic radical; and R° is an optionally substituted amino or imino group such as optionally O-substituted oxyimino, optionally N-substituted hydrazone, or optionally N-substituted semicarbazone; with the proviso that the compound of formula (I) is not a compound of formula (E) or (F)below or a compound disclosed in EP-A-0 307 220. Typically R³ is in the α-configuration. When R is in the β-configuration then it is preferably optionally protected hydroxy, and/or R¹ is preferably. 5 hydrogen, and/or R² is preferably methoxy or optionally protected hydroxy.

EP-A-0 259 779, EP-A-0 293 549, EP-A-0 307 225 and GB-A-2192630 describe compounds of formula (E) :

L0

0 wherein R¹ is optionally protected hydroxy or methoxy. Rm is optionally protected hydroxy, oxo, or an imino group such as optionally O-substituted oxyimino, optionally N-substituted hydrazone, or optionally N-substituted semicarbazone, Rⁿ is 5 methyl, ethyl or isopropyl, and the dashed line is ar double bond or an epoxide group.

EP-A-0 260 536 and EP-A-0 260 537 describe compounds of formula (F) :

wherein R° is optionally protected hydroxy or methoxy, P is hydrogen or a sugar residue, R^ is optionally protected hydroxy, oxo, or an imino group such as optionally 15 O-substituted oxyimino or optionally N-substituted hydrazone, and R^r is isopropyl or sec-butyl.

The above compounds of general formula (I) form the subject of EP-A-0 421 568 (U.S. Patent Application Serial No. 20525,094) which also describes methods of their preparation and indicates preferred substitutents.

A corresponding disclosure exists in the following numbered patent applications of the countries indicated:

25

Australia 55140/90; Canada 2017030; Eire 1785/90; Japan 125638/90; Mexico 21897; New Zealand 233680; Portugal 94075; South Africa 90/3703; South Korea 7054/90; Taiwan (ROC) 79104620.

30

The disclosure of the above-mentioned patent applications is incorporated herein by reference. Preferably the compound used in the present invention is VS 54396 or VS 55759 disclosed respectively in Example 6 (Z- and E-isomers) and in Example 36 (E-isomer) of EP-A-0 421 568 (U.S. Patent Application serial No. 52ξ,094) The preparation of these compounds is illustrated below as Examples 1 and 2.

Reference Example

23 Oxo-25 (S) -t-butyl milbemycin x

5 To a solution of (4S)-5,5-dimethyl-4-triethylsilyloxy- 1-hexyne (8.3 g, 33 mmol) in THF (100 ml) at -78°C under a nitrogen atmosphere was added butyllithium (1.6M in hexane, 18.9 ml, 30 mmol) dropwise over a period of 5 mins. and the mixture stirred at -78°C for a further 3 H. A solution of 10 VS 48927 prepared as described in Examples 1 to 3 of EP-A- 0319142 (4.8g, 8.6 mmol) in THF (20 ml) was added to the mixture which was stirred at -78°C for a further 15 mins. The reaction was quenched with a cold solution (—20°C) of glacial acetic acid (10 ml) in THF (10 ml) and the mixture 15 was then allowed to warm to 0°C. Brine (100 ml) was added and the mixture was extracted with ether (3 x 100 ml) . The combined organic extracts were washed with water, dried (MgSO^) and evaporated to an approximate volume of 50 ml. Methanol (50 ml) was added and the solution again evaporated 20 to an approximate volume of 50 ml. 4-Toluenesulphonic acid (lg) was added and the mixture stirred at 20°C for 1 h.

Sodium bicarbonate (100 ml) was added to the mixture and the whole extracted with dichloromethane (3 x 100 ml) . The

25 combined organic extracts were washed with brine (10^*0 ml) , dried (MgS0₄) and evaporated. The residue was purified by column chromatography (silica eluted initially with dichloromethane and subsequently gradient eluted with 10-60% ethyl acetate in hexane) to afford the methylacetal (3.35g,

30 66%) .

This product (3.35g 5.7 mmol) was dissolved in methanol (25 ml) and a solution of mercuric oxide (56 mg, 0.26 mmol) water (3.5 ml) and concentrated sulphuric acid (0.75 ml, 35 14 mmol)was added dropwise at 20°C. The mixture was stirred at 20°C for 2 h., water was added and the mixture was extracted with dichloromethane (3 x 100 ml) . The combined organic layers were washed with sodium bicarbonate solution (100 ml) , dried (MgS0₄) and evaporated to give the title ketone (3.2g)) pure by nmr + tic.

Example 1

VS 54396 (=Z-isomer)

523-Oxo-25 (S_)-t-butyl milbemycin X (50 mg, 0.09 mmol) was dissolved in methanol (5 ml) . A solution of methoxylamine hydrochloride (50 mg, 0.60 mmol) in water (2 ml) was added and the mixture stirred at room temperature (lh) . The reaction mixture was concentrated and then treated with 0 water (30 ml) and extracted with ether (3 x 15 ml) . The combined ethereal extracts were dried (MgS0₄) and evaporated. The 1:1 mixture* of Z and E oximes was separated by silica gel preparative thin layer chromatography with hexane - ethyl acetate, 1:1 as eluant.

The 23 (ZJ-methoxyimino-25 (S_.)-t-butyl milbemycin X was obtained as a white solid (yield 16 mg) . ^•*/_{z t}-_f-p_^ Na⁺/Noba) 622 [MNa]⁺ 50% (relative intensity). Hplc retention time = 7.7 mi .

The 23 (E -methoxyimino-25 (S -t-butyl milbemycin X was obtained as a white solid (yield 16 mg) . 1_{1 (}FAB ^Na+/^Nofc>^a) 622 [MNa]⁺ 25% (relative intensity). Hplc retention time = 7.9 min.

Hplc conditions : Dynamax C18 column (25 cm x 4.6 mm id) eluted with methanol - water , 9 : 1 at 1 ml/min monitored at 245 nm.

* Ratio is dependent upon the pH of the reaction mixture Example 2

VS 55759 (=E-isomer)

To a solution of 23-oxo-25(S)-t-butyl milbemycin X

(60 mg 0.1 mmol) and sodium acetate (300 mg, 2.2 mmol) in methanol (3 ml) was added 0-t-butylhydroxylamine hydrochloride (50 mg, 0.4 mmol). The mixture was stirred at 20°C for 1 h., water (10 ml) was added and the whole mixture extracted with dichloromethane (3 x 15 ml) . The combined organic extracts were washed with water, dried (MgSO^) and evaporated to dryness. Purification by preparative t.l.c, (silica taper plate (Analtech^R) eluted with ethyl acetate/hexane 2:5) yielded a 4:1 mixture of E:Z oxime isomers (54 mg) . Treatment of a portion of this mixture (30 mg) with methanol (2 ml) and hydrochloric acid (IM, 0.2 ml) gave a 1:1 E:Z ratio of oxime isomers. The two isomers were separated by preparative t.l.c. (silica taperplate eluted four times with chloroform) .

23 (Z)-t-butyloxyimino-25 (S)-t-butyl milbemycin X: tic R_f= 0.5 (Silica eluted three times with chloroform containing 1.5% ethanol) m/z (FAB Na⁺/Noba) (relative intensity) 664 [MNa]⁺ (95%).

23 (E)-t-butyloxyimino-25 (S)-t-butyl milbemycin X: tic R_f=0.45 (Silica eluted three times with chloroform containing 1.5% ethanol) m/z (FAB Na⁺/Noba) (relative intensity) 664 [MNa]⁺ (95%).

Hplc retention times : Dynamax 60A Silica column (25 cm x 4.6 mm id) eluted with chloroform/methanol 99:1 at 1 ml/min monitored at 245 nm. Retention time 23-Z isomer = 14.2 min.

Retention time 23-E isomer = 15.4 min.

In-vivo Testing of US 515759 against sea-lice

Method

Sixty juvenile salmon (Salmo salar) were transferred to fibreglass tanks (measuring 1.45m x 1.45m, with a water depth of 0.3m) and given a 24 hour acclimation period. All tanks were supplied with flow through sea water and were aerated. Temperature and salinity were 14°C and 32ppt respectively.

Salmon were anaesthetised with 0.075% benzocaine solution and soaked in a small mesh lined container with large numbers of Adult and pre adult (male and female) sea lice (Lepeophtheirus salmonis) Fish were removed from the infection bath when a minimum of 10 lice could be seen attached to them. All fish were placed into a single tank (as above) and allowed 24 hours to recover.

Individual groups of ten fish were randomly selected and placed into a large container with 501 of sea water and an appropriate amount of concentrated stock solution of VS 55759 (90 mg in 100 ml absolute alcohol) added to achieve the desired treatment concentration. Aeration was used during all treatments. Treatments were one hour in -duration after which fish were removed and place into individual tanks for recovery. Temperature and salinity during treatments were 14°C and 32ppt respectively.

After 24 hours, fish were sacrificed and number of lice per fish were recorded. Feed was withheld throughout the entire experiment. Results

VS 55759 was effective in removing all lice at 0.1 ppm (5.55 ml of stock solution in 501 sea water) and significantly efficacious at 0.05 ppm (2.78 ml of stock solution in 501) where only 4 lice were found after treatment. No fish mortalities were recorded during treatment at these dosages.

Claims

1. Use of a compound of formula (I) :

(I)

wherein R¹ is hydrogen or optionally protected hydroxy; R² is alkoxy, optionally protected hydroxy, oxo or optionally O-substituted oximino; R³ is hydrogen, optionally protected hydroxy,or a group 4'- (α-jL-oleandrosyl)-α-L-oleandrosyloxy or α-L- oleandrosyloxy wherein the terminal hydroxy group is optionally protected; R⁴, R⁵, R⁶ and R⁷ are the same or different and each is hydrogen or an organic radical; and R⁸ is an optionally substituted amino or imino group such as optionally O-substituted oxyimino, optionally N-substituted hydrazone, or optionally N-substituted semicarbazone; with the proviso that the compound of formula (I) is not a compound of formula (E) or (F) as defined hereinabove or a compound disclosed in EP-A-0 307 220, for the manufacture of a medicament for the treatment or prophylaxis of endo and ectoparasitic infestations in fish.

2. Use according to claim 1, for the treatment of infestations of parasitic copepods or sea-lice in salmonids. Use according to claim 1 or 2, wherein R , R , R , R- and R are hydrogen, R² is hydroxy, R is t.-butyl, and R⁸ is methoxyimino or t.-butyloxyimino (E- or Z-isomer or mixture 5 thereof) .

4. A method of treatment or prophylaxis of endo- and ectoparasitic infestations, which comprises administering an effective non-toxic amount of a compound of formula (I) as

10 defined in claim 1 to a fish in need thereof.

5. A pharmaceutical composition for use in the treatment of endo- and ectoparasitic infestations in fish, which comprises a compound of formula (I) as defined in claim 1

15 and a pharmaceutically acceptable carrier.

6. A composition according to claim 5, in the form of a feed additive.

207. A composition according to claim 5, in the form of a spray or dip.