WO1993020072A1

WO1993020072A1 - (furan-2-yl)-2-(1-normon-2-yl) oxazole derivatives with antibacterial activity

Info

Publication number: WO1993020072A1
Application number: PCT/GB1993/000596
Authority: WO
Inventors: Peter John O'hanlon; John Stephen Elder
Original assignee: Smithkline Beecham P.L.C.
Priority date: 1992-04-02
Filing date: 1993-03-23
Publication date: 1993-10-14
Also published as: GB9207214D0; IL105231A0; MA22849A1; SI9300172A; AU3763193A; MX9301893A; EP0633884A1; JPH07505379A; ZA932302B; CN1091427A

Abstract

A compound of formula (I) in which R1 represents a 2-nitro-furan-5-yl group which may be further substituted by up to two additional substituents and Z¿1?, Z2 and Z3 which may be the same or different is each hydrogen or a hydroxyl protecting group. These (furan-2-yl)-2-(1-normon-2-yl) oxazole derivatives are of use in antibacterial therapy.

Description

(Furan-2-yl )-2-(l normon-2-yl ) oxazole derivatives with antibacterial activity

The present invention relates to a class of compounds having antibacterial and antimycoplasmal activity, to processes for their preparation and to their use in human and veterinary medicine and also to intermediates for use in the preparation of such compounds.

Compounds of the general formula (A):

(A) in which the group R° represents an optionally substituted 5-membered heteroaryl ring containing from 1 to 4 heteroatoms selected from oxygen, nitrogen and sulphur, have been previously disclosed in EP-A-0 087 953 (Beecham Group pic) and EP-A-0 123 378 (Beecham Group pic) and will be recognised as derivatives of monic acid A in which the carboxylic acid group thereof has been replaced by the group R°. Such compounds were shown to have antibacterial and antimycoplasmal activity. Amongst the compounds of formula (A) described in EP-A-0 087 953 are examples in which the group R° is oxazolyl, substituted with a range of groups including substituted phenyl, substituted alkyl and thienyl. In addition EP-A-0 399 645 and WO-A- 91/09586 (Beecham Group pic) disclose compounds of formula (A) in which R° is an oxazol-2-yl group further substituted at position 5 by a furyl, isoxazolyl or pyridyl group. Surprisingly, it has now been found that with the 5- furyloxazol-2-yl compounds, there is a sub-class of compounds which have enhanced biological activity. Accordingly, the present invention provides a compound of formula

(I):

(I) in which R* represents a 2-nitro-furan-5-yl group which may be further substituted by up to two, preferably one, additional substituents and Zj_, Z2 and Z3 which may be the same or different is each hydrogen or a hydroxyl protecting group. It will be appreciated that the group Rl may be represented by the sub-formula:

Xxp in which R^a and R" each denote optional substituents. Suitable values for

R^a and ^ include, for example (Cι_6)alkyl and halogen. Preferably Rl is 5- nitro-furan-2-yl. When used herein, the term 'halogen' refers to fluorine, chlorine, bromine and iodine.

Compounds of formula (I) may conveniently be named as '(1-normon-

2-yl)oxazoles'. Normonyl is the trivial name for the 3-[(2S,3R,4R,5S)-5-

[(2S,4S,5S)-2,3-epoxy-5-hydroxy-4-methylhexyl]-3,4-dihydroxy- tetrahydropyran-2-yl]-2-methylprop-l(E)-enyl radical, as shown in formula

(II):

(II) It will be appreciated that in compounds of formula (I), the chiral centres of the radical of formula (II) will have the same absolute configuration as the corresponding radical in monic acid A.

Since the compounds of the present invention are intended for use in pharmaceutical compounds, it will be appreciated that preferred compounds of formula (I), are pharmaceutically acceptable i.e. are compounds of formula (la):

(la) in which R¹ is as hereinbefore defined.

Since the compounds of formula (la) of the present invention are intended for use in pharmaceutical compositions, it will be understood that they are each provided in substantially pure form, for example at least 50% pure, more suitably at least 75% pure and preferably at least 95% pure (% are on a wt wt basis). Impure preparations of the compounds of formula (la) may be used for preparing the more pure forms used in the pharmaceutical compositions. Although the purity of intermediate compounds of the present invention is less critical, it will be readily understood that the substantially pure form is preferred as for the compounds of formula (la). Preferably, whenever possible, the compounds of the present invention are obtained in crystalline form.

When some of the compounds of this invention are allowed to crystallise, or are recrystallised, from organic solvents, solvent of crystallisation may be present in the crystalline product. This invention includes within its scope such solvates. Similarly, some of the compounds of this invention may be crystallised or recrystallised from solvents containing water. In such cases water of hydration may be formed. This invention includes within its scope stoichiometric hydrates as well as compounds containing variable amounts of water that may be produced by processes such as lyophilisation. Examples of compounds within this invention include 5-(5-nitrofuran-

2-yl)-2-(l-normon-2-yl)oxazole which has the following formula:

and derivatives thereof in which sme or all of the hydroxyl groups are protected with hydroxyl-protecting groups.

Compounds of formula (I) can be prepared by analogy with the methods described in EP-A-0 399 645 and WO-A-91/09586 (Beecham Group). In particular, the present invention provides a process for preparing a compound of formula (I) which process comprises cyclising a compound of formula (III):

am in which \_ -, Z]_, Z2 and Z3 are as hereinbefore defined, to form a compound of formula (I) and thereafter, and if necessary, removing any hydroxyl- protecting groups.

Compounds of formula (III) may be cyclised using a carboxylic anhydride or mixed anhydride or an acid chloride, such as trifluoroacetic anhydride or trichloroacetic anhydride or trichloroacetyl chloride, which latter is preferably used in the presence of pyridine and 4-dimethylamino- pyridine. In this reaction, the hydroxyl groups of the l-normon-2-yl radical become acylated and must subsequently be deprotected. Trihaloacetyl groups formed during cyclisation may be removed using potassium carbonate in solvents such as water, alkanols or admixtures thereof. Appropriate deprotecting conditions for removing other acyl residues will be readily apparent to the skilled person. Alternatively, the hydroxyl groups of the 1- normon-2-yl radical maybe protected, prior to cyclising with a carboxylic anhydride, and deprotected by conventional methods such as described below.

The cyclisation of a compound of formula (III) may also be suitably effected using a chlorinating agent such as phosphorus oxychloride, phosgene, thionyl chloride or phosphorus pentachloride, in the presence of a tertiary amine, such as triethylamine or pyridine. Such a reaction is conveniently effected in an organic solvent, for instance dichloromethane or tetrahydrofuran, at from reduced to elevated temperature, for instance -80 to +100°C, over a period of several hours to a few days. Preferably phosgene or phosphorus oxychloride is used, at a temperature of from 0 to 20°C.

Alternatively, cyclisation may be effected using triphenylphosphine and carbon tetrachloride as the chlorinating reagent, in the presence of a tertiary amine, for instance triethylamine, in an inert solvent such as acetonitrile or acetonitrile/pyridine. This type of process is described by H. Vorbruggen and K. rolikiewicz in Tetrahedron Lett., 1981, 4471; it is particularly advantageous in that the formation of compounds of formula (III) and cyclisation of these to compounds of formula (I) may be conducted in situ.

Compounds of formula (III) as defined above are novel and useful as chemical intermediates in the aforementioned process. Accordingly, the present invention also provides a compound of formula (III), as hereinbefore defined.

Compounds of formula (III) may be produced from monic acid A by analogy with the reaction sequence previously described in EP-A-0 087 953 (Beecham Group pic). Suitably, monic acid A is initially converted to an activated derivative, for instance a mixed anhydride such as that formed by reaction with iso-butylchlorformate in the presence of a suitable base such as triethylamine; followed by reaction of this intermediate with an amine hydrochloride salt of the formula (IV): RlCOCH₂NH₃+Cl" (IV) wherein Rl is as hereinbefore defined; in the presence of a suitable base such as triethylamine.

It will be appreciated that the compounds of formula (IV), as hereinbefore defined, are furans with β-aminoketones side chains and these may be obtained from starting materials which are either well known or readily available or produced by conventional processes, for instance, by analogy with the methodology described in Organic Preparations and

Procedures Int., 22(4), 399-484, 1990.

The present invention also provides a process for the preparation of a compound of formula (I) which process comprises reacting a compound of formula (V):

(V) in which Z , Z₂ and Z3 are the same or different and each is hydrogen or a hydroxyl-protecting group; with a compound of formula (VI):

(VI) in which R is as hereinbefore defined; M+ is a metal cation, preferably an alkali metal cation, most preferably a lithium or sodium cation; and R2 is an anion-stabilising group which will spontaneously eliminate with a β-hydroxyl group to produce an olefin, preferably a trialkylsilyl or a dialkylphosphonate group, most preferably trimethylsilyl or diethylphosphonate; and, thereafter and if necessary, removing any hydroxyl-protecting groups. The reaction of a compound of formula (V) with a compound of formula (VI) may conveniently be effected in an organic solvent, such as tetrahydrofuran, diethyl ether or dimethyl sulphoxide, at from reduced to elevated temperature, such as from -80° to +100°C.

The compound of formula (V) in which each of Z , Z₂ and Z3 is hydrogen, and processes for its production, are described in GB 1 587 060.

Derivatives thereof wherein Z , Z₂ and Z3 are hydroxyl-protecting groups may be produced by conventional methods such as those mentioned below.

When this compound is produced with hydroxyl protecting groups already in place it may be used directly or even in situ in the above reaction or it may be optionally deprotected and/or isolated.

The compounds of formula (VI) may be prepared by conventional processes, by analogy with those as described in EP-A-0 123 378 (Beecham

Group pic). For instance, a compound of formula (VII):

(VII) wherein W is hydrogen or halogen and R^ is as hereinbefore defined, may be converted into a compound of formula (VI) in which M is lithium and 2 is trimethylsilyl, according to the methodology of W.S. Wadsworth Jr, Organic Reactions, 1977, 25, 73; and by E.J. Corey and D.L. Boger, Tetrahedron, 1978, 5; T.H. Chan,, Ace Chem. Res. 1977, 10, 442. Alternatively, a compound formula (VII) may be converted to a compound of formula (VI) in which M is an alkali metal and R^ is diethylphosphonate, by anology with the method of B.H. Lipshutz and K.W. Hungate, J. Org. Chem., 1981, 46, 1410. It will be appreciated that compounds of formula (VII), as hereinbefore defined, are 2-substituted-5-(furan-2-yl)oxazoles and are either well known and readily available or may be produced by conventional processes. The synthesis of oxazoles is reviewed in 'Comprehensive Heterocyclic Chemistry', ed. Katritzky and Rees, 6, Chapter 4.18. By way of illustration, a convenient synthetic strategy uses as its starting point a furanyl derivative, for instance a compound of formula (IV), as hereinbefore defined, which may then be converted to a compound of formula (VII), by the analogy with the methodology described by J.L. La Mattina, J. Urg. Chem.,

1980, 45, 2261.

The present invention further provides a process for the preparation of a compound of formula (I) which process comprises treating a compound of formula (Vπi):

(VIII) in which Rl, Z , Z₂ and Z3 are as hereinbefore defined, and Y is a leaving group; with a strong base, and thereafter and if necessary removing any hydroxyl-protecting groups, by analogy with the process described in EP-A-0 399 645 (Beecham Group pic). Suitable values for Y include, for instance, aryl sulphonyl, for example p-toluenesulphonyl, alkylsulphonyl, alkyl or aryl sulphinyl, quaternary ammonium, for example trialkylammonium, and dialkoxy phosphine oxide. Suitable strong bases include for example 1,8- diazo-bicyclo[5.4.0]undec-7-ene (DBU) and l,5-diazobicyclo[4.3.0]non-5-ene (DBN). Suitably the reaction is effected in a solvent such as acetonitrile, and at a temperature in the range from -20 to +80°C.

Compounds of formula (VIII) as hereinbefore defined are novel and useful as intermediates in the aforementioned processs. Accordingly, the present invention also provides a compound of formula (VIII), as hereinbefore defined.

Compounds of formula (VIII) may be prepared by treating a compound of formula (IX):

(IX) in which Z\, Z₂ and Z3 are the same or different and each is hydrogen or a hydroxyl-protecting group, and Y is as hereinbefore defined, with a compound of formula (X):

RiCHO (X) in which R* is as hereinbefore defined, or a corresponding analogue thereof in which the aldehyde functionality of the compound formula (X) is masked, under dehydrating conditions. Suitable dehydrating conditions are similar to those hereinbefore described in respect of the cyclisation of a compound of formula (III) to give a compound of formula (I). Particularly suitable conditions include the use of triphenylphosphine in combination with carbon tetrachloride or hexachloroethane, in the presence of triethylamine.

The preparation of compounds of formula (IX) is described in EP-A-0 399 645 (Beecham Group pic).

Compounds of formula (X) are recognisable as aldehyde derivatives of furan and are either available commercially or well known or prepared from readily available starting materials by the adaptation of standard methodology.

It will be appreciated that, in certain cases, it will be more convenient to generate a compound of formula (VHI) in situ (by reacting a compound of formula (IX) with a compound of formula (X) as hereinbefore described) and then carry it through to a compound of formula (I), as hereinbefore described, in a "one-pot" procedure, without isolating the intermediate compound.

The present invention also provides a process for preparing a compound of formula (I) which process comprises isomerising the carbon- carbon double bond of a compound of formula (XI):

(XI) in which R Z , Z₂ and Z3 are as hereinbefore defined; by methods known for the isomerisation of a carbon-carbon double bond. Suitable isomerisation methods are described by Sonnet in Tetrahedron, 1980, 36, 557 and include photo-chemical and addition-elimination methods. A compound of formula (XI) may be obtained by treating a compound of formula (V) with a compound of formula (VI), as hereinbefore described. This reaction is lacking stereoselectivity and may lead to the formation of compounds of formulae (I) and (XI), which may then be separated by conventional procedures such as chromatography.

When used herein, the term 'hydroxyl-protecting group' refers to any such group known in the art which may be removed without disruption of the remainder of the molecule. Suitable hydroxyl-protecting groups are described in 'Protective Groups in Organic Synthesis', T.W. Greene, Wiley-Interscience, New York, 1981.

The hydroxyl groups of monic acid A, and compounds of formulae (III), (V), (VIII), (IX) and (XI) may be protected at any stage of the above processes, using conventional methods. The hydroxyl-protecting group may be removed by methods known in the art, including enzymatic methods. Particularly suitable hydroxyl-protecting groups are silyl groups since these are readily removed under mild conditions. Such groups are introduced using conventional silylating agents, includin halosilanes and silazanes, for example those of the following formulae :

L₃SiY; L₂SiY₂; L₃SiNL₂; L₃SiNHSiL₃; L₃SiNHCOL; L₃SiO-C(L)=NSiL₃; L₃SiNHCONHSiL₃; LNHCONHSiL₃; tBuMe₂Si-O-SO₂-CF₃;

Me₃Si- N^ N BuMe₂Si- N^ N

in which Me denotes methyl, t-Bu denotes t-butyl, X is halogen and each group L is independently selected from hydrogen, (Ci"6)alkyl, (Cι-g)alkoxy, aryl or aryl(Cι-4)alkyl. A preferred silyating agent is trimethylsilyl chloride. Particularly suitable hydroxyl-protecting groups are trimethylsilyl, triethylsilyl and t-butyldimethylsilyl groups. Preferred hydroxyl-protecting groups are trimethylsilyl groups because of their ease of removal.

The glycol function of monic acid A and of the compounds of formulae (III), (V), (VIII), (IX) and (XI) may be protected by forming a cyclic derivative using a compound of formula (XII):

R C(OR⁴)(OR5)(OR⁶) (XΠ) wherein R³ is hydrogen or (Ci-gtølkyl and each of R⁴, R^ and R^ is (C^- β)alkyl such that in the cyclic derivative Z* and Z^ together are a moiety R3C(0R4). Suitably R³ is hydrogen, methyl, ethyl, n- or iso-propyl; most suitably it is hydrogen. The groups R⁴, Εβ and R*> are suitably methyl, ethyl, 7i- or iso-propyl, or n-, iso-, sec- or t-butyl; most suitably methyl. The hydroxyl groups of a compound of formula (I) may also be protected prior to conversion to a further compound of formula (I) as described above. In each case the protecting groups described above may be removed by mild acid hydrolysis followed by alkaline hydrolysis, for instance, as described by Clayton et al, J.C.S. Perkin Trans. 1, 1979, 308. This invention also provides a pharmaceutical or veterinary composition which comprises a compound of formula (I) (hereinafter referred to as the 'drug') together with a pharmaceutically or veterinarily acceptable carrier or excipient. The compositions may be formulated for administration by any route, and would depend on the disease being treated. The compositions may be in the form of, for instance, tablets, capsules, powders, granules, suppositories, lozenges and liquid or gel preparations, including oral, topical and sterile parenteral suspensions.

Tablets and capsules for oral administration may be in unit dose presentation form, and may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinyl-pyrollidone; fillers, for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricants, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants, for example potato starch, or acceptable wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in normal pharmaceutical practice. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example sorbitol, syrup, methyl cellulose, glucose syrup, gelatin, hydrogenated edible fats; emulsifying agents, for example lecithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters, glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and if desired conventional flavouring or colouring agents. For topical application to the skin the drug may be made up into a cream, lotion or ointment. Cream or ointment formulations that may be used for the drug are conventional formulations well known in the art, for example, as described in standard text books of pharmaceutics and cosmetics, such as 'Harry's Cosmeticology' published by George Godwin, London, and the British Pharmacopoeia.

Suppositories will contain conventional suppository bases, e.g. cocoa-butters or other glyceride.

For parenteral administration, fluid unit dosage forms are prepared utilizing the drug and a sterile vehicle. The drug, depending on the vehicle and concentration used, can be suspended in the vehicle. Advantageously, adjuvants such as a local anaesthetic, preservative and buffering agents can be dissolved in the vehicle. To enhance the stability the composition can be frozen after filling into the vial and water removed under vacuum. The dry lypophilized powder is then sealed in the vial. The drug can be sterilised by exposure to ethylene oxide before suspending in the sterile vehicle.

Advantageously, a surfactant or wetting agent is included in the composition to facilitate uniform distribution of the drug. For topical application to the ear, the drug may be made up into a suspension in a suitable liquid carrier, such as water, glycerol, diluted ethanol, propylene glycol, polyethylene glycol or fixed oils. For topical application to the eye, the drug is formulated as a suspension in a suitable, sterile aqueous or non-aqueous vehicle. Additives, for instance buffers such as sodium metabisulphite or disodium edetate; preservatives including bactericidal and fungicidal agents, such as phenylmercuric acetate or nitrate, benzalkonium chloride or chlorhexidine, and thickening agents such as hypromellose may also be included.

The dosage employed for compositions administered topically will, of course, depend on the size of the area being treated. For the ears and eyes each dose will typically be in the range from 10 to 100 mg of the drug.

Veterinary compositions for intramammary treatment of mammary disorders in animals, especially bovine mastitis, will generally contain a suspension of the drug in an oily vehicle. The compositions may contain from 0.1% to 99% by weight, preferably from 10-60% by weight, of the drug, depending on the method of administration. Where the compositions are in unit dose form, each dosage unit will preferably contain from 50-500 mg, of the drug. The dosage as employed for adult human treatment (average weight about 70 kg) will preferably range from 100 mg to 3 g per day, for instance 250 mg to 2 g of the drug per day, depending on the route and frequency of administration. Alternatively, the drug may be administered as part of the total dietary intake of a non-human animal. In this case the amount of drug employed may be less than 1% by weight of the diet and in preferably no more than 0.5% by weight. The diet for animals may consist of normal foodstuffs to which the drug may be added or the drug may be included in a premix for admixture with the foodstuff. A suitable method of administration of the drug to animals is to add it to the non-human animal's drinking water. In this case a concentration of the drug in the drinking water of about 5-500 μg/ml, for example 5-200 μg ml, is suitable.

The compounds of this invention are useful for the treatment of bacterial and mycoplasma-induced infections in animals, including humans, such as the treatment of respiratory tract infections, otitis, meningitis, skin and soft tissue infections in man, mastitis in cattle, and respiratory infections in animals such as pigs and cattle. Accordingly in a futher aspect, the present invention provides a compound of formula (la) as hereinbefore defined for use in therapy. The present invention further provides a method of treating bacterial and/or mycoplasmal infection in human or non-human animals, which method comprises administering a therapeutically effective amount of a compound of formula (I) as hereinbefore defined, to a human or non-human animal in need of such therapy. The present invention further provides for the use of a compound of formula (I) as hereinbefore defined in the manufacture of a medicament for use in anti-bacterial and/or anti- mycoplasma therapy.

The compounds of this invention are active against both Gram negative and Gram positive organisms, including Haemophilus, for instance H.influenzae Ql; Branhamella,foτ instance B.catarrhalis 1502; Streptococci, for instance S.pyogenes CN10 and S.pneumoniae PU7; Staphylococci, for instance S.aureus Oxford; and Legionella, for instance L. pneumophila. In addition, compounds of this invention are active against Staphylococci organisms such as S. aureus and coagulase negative strains of Staphylocci such as iS. epidermidis which are resistant (including multiply-resistant) to other anti-bacterial agents, for instance, β-lactam antibiotics such as, for example, methicillin; macrolides; aminoglycosides, and lincosamides ie compounds of the present invention are useful in the treatment of MRSA, MRCNS and MRSE. Furthermore, compounds of the present invention are useful in the treatment of Staphylococci organisms which are resistant to mupirocin.

The compounds of this invention are also active against mycoplasma- induced infections, in particular infections caused by Mycoplasma fermentans, which has been implicated as a co-factor in the pathogenesis of AIDS. Accordingly in a further aspect, the present invention provides a method of treating humans infected with M. fermentans, in particular humans also infected with HIV, which method comprises treating humans in need of such therapy with an anti-mycoplasmal effective amount of a compound of formula (la).

No adverse toxicological effects are expected from the administration of a compound of formula (la)

The following Example illustrates the invention, but is not intended to limit the scope in any way: Example 1 - 5-(5-Nitrofuran-2-yl)-2-(l-normon-2-yl)oxazole a) 5-(5-Nitrofuran-2-yl)-2-(6,7,13-0-*ris-trimethylsilyl-l-normon-2- yl) oxazole - TVis-trimethylsilyl tosylmethylmonamide (60.0g, 82.4mmol) (EP-A-O 399 645; Example 12(c), Beecham Group pic) was dissolved in acetonitrile (175ml). 5-Nitro-2-furfuraldehyde (14.1g, lOOmmol) was added, followed by triphenylphosphine (30.5g, llβmmol) and triethylamine (54ml, 387mmol). Hexachloroethane (27.5g, llβmmol) was then added portionwise • over twenty minutes, with cooling, keeping the temperature between 18 and 26^SC. The reaction mixture was stirred vigorously for 3h at room temperature, then further portions of triphenylphosphine, triethylamine and hexachloroethane (as above) were added. After fifteen minutes at room temperature l,8-diazabicyclo[5.4.01undec-7-ene (DBU) (49ml, 330mmol) was added, and the mixture stirred for a further fifteen minutes. The mixture was extracted with hexane (5 x 600ml). The combined organic extracts were washed with 2% aqueous sodium hydrogen carbonate solution (400ml) and then with brine (2 x 80ml), dried over magnesium sulphate, filtered and evaporated under vacuum. The black viscous oil was purified by vacuum flash chromatography on silica (1kg), eluting with 0-14% ethyl acetate in hexane, to give the title compound as an orange oily foam (43.0g, 75%); δ^~n (CDC1₃) inter alia 0.91 (3H, d, J 7.1Hz, I7-H3), 1.20 (3H, d, J 6.3Hz, 14-H₃), 2.32 (3H, s, I5-H3), 6.28 (1H, s, 2-H), 6.74 (1H, d, J 3.9Hz, 3"-H), 7.42 (1H, d, 3.9Hz, 4"-H), and 7.62 (1H, s, 4'-H); mlz 694 (Λf+,1%), 605 (1), 117 (100), and 73 (90). (Found: +, 694.3144. C3₂H54N₂O9Si3 requires M, 694.3137). b) 5-(5-Nitro uran-2-yl)-2-(l-normon-2-yl) oxazole - 5-(5-Nitrofuran- 2-yl)-2-(6,7,13-0-tris-trimethylsilyl-l-normon-2-yl) oxazole (43.0g, 61.9mmol) was dissolved in tetrahydrofuran (680ml), and a solution of concentrated hydrochloric acid (1.75ml) in water (140ml) added. The mixture was stirred for 16 minutes, then saturated aqueous sodium hydrogen carbonate solution (26ml) was added, and the mixture extracted with ethyl acetate (2 x 250ml). The combined organic extracts were washed with brine (2 x 80ml), dried over magnesium sulphate, filtered, and reduced to a small volume under vacuum. This oil was stirred vigorously while di-iso-propyl ether (11) was added slowly. This mixture was stirred overnight at room temperature in the dark. The resulting solid was filtered off, washed with di-iso-propyl ether and dried under vacuum to give a yellow powder (28.3g). This material was dissolved in warm acetone (115ml) and stirred while hexane (80ml) was added slowly. The product crystallised out and was stirred for Vάi before more hexane (220ml) was added slowly. After a further &h the mixture was cooled in an ice bath and stirred for Vfch. The product was filtered off, washed with acetone:hexane (1:4, 50ml), then hexane, and dried under vacuum to give a yellow crystalline solid (26.50g, 90%) mp 119-120⁹C; found C, 57.64; H, 6..18;

N, 5.86%; C₂3H3oN₂O9 requires C, 57.73; H, 6.32; N, 5.85%; υ_max (KBr) 3412, 1507, 1451, 1352, 1275, and 1049cm"¹; λ_max (EtOH) 384nm (ε_m

18,819); δπ (CD₃OD) inter alia 0.95 (3H, d, J 7.0Hz, 17-H₃), 1.20 (3H, d, J

6.4Hz, U-H3), 2.31 (3H, s, 15-H₃), 6.28 (1H, s, 2-H), 6.99 (1H, d, 3.9Hz, 3"-

H), 7.59 (1H, d, 3.9Hz, 4"-H), and 7.69 (1H, s, 4'-H); δc (CD3OD) 12.3 (C-

17), 20.0 (C-15), 20.3 (C-14), 33.0 (C-9), 41.7 (C-8), 43.7 (C-12), 44.0 (C-4), 56.9 (C-10), 61.3 (C-11), 66.4 (C-16), 70.0 (C-6), 70.7 (C-13), 71.6 (C-7), 76.4 (C-5), 110.5, 112.9, 114.9 (C-2, C-3", C-4"), 128.2 (C-4'), 141.1, 146.9 (C-5\ C- 2"), 152.4, 153.2 (C-3, C-5"), and 164.1 (C-2'); m/z 478 ( +: 15%), 234 (100), 121 (74), and 75 (75). (Found: M+, 478.1948. C₂3H oN₂O₉ requires M, 478.1951).

Biological Data

(a) The activity of the compound of Example 1 against various bacteria {H.influenzae Ql; B.catarrhalis 1502; Strep.pyogenes CN10; Strep.pneumoniae PU7; and Staph.aureus Oxford) which are important in the diseases of humans was assayed in vitro using serial dilutions in nutrient agar with 5% chocolated horse blood. The MIC values were determined after incubation for 18h at 37°C and were found to be in the range 0.03 to 0.06 μg/ml.

(b) In addition, the antibacterial activity of the compound of Example 1 against the Legionella organism, L.pneumophila 1624, serogroup 1, was assayed using colonies grown from culture thawed from frozen skim milk stocks and streaked onto supplemented buffered charcoal yeast extract agar (BCYEa, Oxoid). These colonies were then suspended in a tissue culture medium (TCM=Eagle's Minimal Essential Midium + Earles' salts supplemented with 10% foetal calf serum, 2mM L-glutamine and 1% non- essential amino acids) to MacFarland's barium sulphate opacity standard 0.5. The suspension was further diluted 1:100 in TCM to yield a final inoculum of 4.83 x 10^ cfu/ml.

Human foetal lung fibroblast (MRC-5) cells were prepared by growing to 80% confluency in 6-well plates, removing the medium and then washing the monolayers twice with Dulbecco's PBS). These cells were then inoculated and after 16 hours, the medium was removed and the inoculated monolayers washed twice to remove any adherent, non-intracellular, organisms.

Test compound, prepared to the required concentrations in TCM, was added to the cells. The compound of Example 1 was tested at 0.5, 2 and

8mg ml whilst erythromycin at 0.5 and 2mg/ml was used as a control. At 0, 3, 12, 24, 36, 48 and 72h after the dose, the medium was removed from one well/treatment, and the monolayers washed twice. Sterile distilled water was added and left for 30 min to lyse the cells. After vigorous trituration, the lysate was serially diluted in Mueller Hinton brother and plated onto BYCEa and 5% horse blood agars. Colonies oiL.pneumophila were counted after 72h incubation at 37°C. Positive antibacterial activity against L. pneumophlia was observed.

The stability of the compounds in TCM was confirmed over a 72h period. Solutions of 2 mg/ml of each of the compounds were prepared in TCM and incubated at 37°C or 4°C and aliquots were removed at intervals. The compund of Example 1 and erythromycin were assayed against Bacillus subtilis ATCC 6633 and Sarcina lutea NCTC 8340, respectively, using standards prepared in TCM.

Claims

1. A compound of formula (I):

(I) in which R¹ represents a 2-nitro-furan-5-yl group which may be further substituted by up to two additional substituents and Z , Z₂ and Z3 which may be the same or different is each hydrogen or a hydroxyl protecting group.

2. A compound as claimed in claim 1 in which Z\, Z₂ and Z3 is each hydrogen.

3. A compound as claimed in claim 1 or claim 2 in which substituents for the furanyl group of R¹ are selected from (Cι.g)alkyl and halogen.

4. A compound as claimed in any one of claims 1 to 3 in which Rl is a 5- nitro-furan-2-yl group.

5. The compound of formula (I) as defined in claim 1 which is 5-(5- nitrofuran-2-yl)-2-(l-normon-2-yl)oxazole; or a derivative thereof in which some or all of the hydroxyl groups are protected with hydroxyl-protecting groups.

6. A process for preparing a compound of formula (I) as defined in claim 1 which process comprises:

(a) cyclising a compound of formula (III):

(in) in which R Z\, Z and Z3 are as defined in claim 1, to form a compound of formula (I); (b) reacting a compound of formula (V):

(V) in which Z , Z and Z3 are as defined in claim 1; with a compound of formula (VI):

(VI) in which R¹ is as defined in claim 1; M⁺ is a metal cation; and R^ is an anion-stabilising group which will spontaneously eliminate with a β-hydroxyl group to produce an olefin;

(c) treating a compound of formula (VIII):

(VIII) in which Rl, Z , Z₂ and Z3 are as defined in claim 1, and Y is a leaving group; with a strong base;

(d) treating a compound of formula (IX):

(IX) in which Z , Z₂ and Z3 are the same or different and each is hydrogen or a hydroxyl-protecting group, and Y is as hereinbefore defined, with a compound of formula (X):

RiCHO (X) in which R¹ is as hereinbefore defined, or a corresponding analogue thereof in which the aldehyde functionality of the compound formula (X) is masked, under dehydrating conditions, to generate an intermediate compound of formula (VIII) as hereinbefore defined iτι situ, and then, without isolating the thus formed intermediate compound, treating said intermediate with a strong base; or

(e) isomerising the carbon-carbon double bond of a compound of formula i

(XI) in which R¹, Z , Z and Z3 are as hereinbefore defined;

and, thereafter and if necessary, removing any hydroxyl-protecting groups.

7. A pharmaceutical or veterinary composition comprising a compound of formula (I) as defined in claim 2 and a pharmaceutically or veterinarily acceptable excipient.

8. A compound of formula (I) as defined in claim 2 for use in therapy.

9. The use of a compound of formula (I) as defined in clai 2 for the manufacture of a medicament for use in anti-bacterial or anti-mycoplasma therapy.

10. A method of treating bacterial or mycoplasmal infection in a human or non-human animal, which method comprises administering a therapeutically effective amount of a compound of formula (I) as defined in claim 2, to a human or non-human animal in need of such therapy.

11. A compound of formula (III) as defined in claim 6.

12. A compound of formula (VIII) as defined in claim 6.

13. A process for preparing a compound of formula (VIII) which process comprises treating treating a compound of formula (IX):

(DO in which Z\, Z₂ and Z3 are as defined in claim 1, and Y is a leaving group, with a compound of formula (X):

RiCHO (X) in which R¹ is as defined in claim 1, or a corresponding analogue thereof in which the aldehyde functionality of the compound formula (X) is masked, under dehydrating conditions.