Patent Description:
We are currently facing a worldwide pandemic of multidrug resistant bacteria, arising from the long-term use of antibacterials. Antibacterial overavailability and poor prescribing practices have allowed exposure to sub-optimal concentrations of antibacterials, promoting the evolution of environmental resistance mechanisms in bacteria.

There is therefore a continuing need to develop new compounds and strategies for combating unwanted bacterial growth, particularly in bacteria that are resistant to existing drugs.

Teixobactin is a recently-discovered depsipeptide antibiotic that acts through a novel mechanism of action (<NPL>). Teixobactin inhibits bacterial cell wall synthesis by binding to precursors of essential cell wall components. As such, it is likely to induce resistance at a considerably slower rate than antibacterials that act at intracellular protein targets.

Teixobactin's unusual structure comprises D-amino acid residues, and an L-allo-enduracididine residue. The manufacture of Teixobactin in a commercial scale is difficult and expensive, in part due to the presence of the L-allo-enduracididine residue.

Various analogues of Teixobactin have been described in the literature, including in <NPL>; <NPL>; <NPL>; <NPL>; <NPL>; <NPL>; and <NPL> advanced online publication. <NPL> discusses the synthesis and structure-activity relationship of teixobactin analogues. <NPL> describes investigations of N-terminal substitution and D-residues of teixobactin. <NPL> discusses the antibiotic capabilities of teixobactin. <CIT> and is entitled "Novel depsipeptide and uses thereof". <CIT> and is entitled "Antimicrobial Compositions".

The inventors have now found a new range of analogues of Teixobactin that is easily-accessible and displays potent antimicrobial activity, and have developed robust processes for their synthesis.

The listing or discussion of an apparently prior published document in this specification should not necessarily be taken as an acknowledgement that the disclosure of the document is part of the state of the art or is common general knowledge.

According to a first aspect of the invention, there is provided a compound of formula IA,
<CHM>
or a pharmaceutically-acceptable salt, solvate or clathrate thereof, wherein:.

Such compounds, salts, solvates and clathrates are referred to hereinafter as the "compounds of the invention".

We also disclosed compounds of formulae IB and IC, which do not fall within the literal scope of the claims:
<CHM>
<CHM>
or a pharmaceutically-acceptable salt, solvate or clathrate thereof, wherein:.

By "pharmaceutically-acceptable salt" we mean an acid addition or base addition salt suitable for use in pharmaceuticals. Such salts may be formed by conventional means, for example by reaction of a free acid or a free base form of a compound of the invention with one or more equivalents of an appropriate acid or base, optionally in a solvent, or in a medium in which the salt is insoluble, followed by removal of said solvent, or said medium, using standard techniques (e.g. in vacuo, by freeze-drying or by filtration). Salts may also be prepared by exchanging a counter-ion of a compound of the invention in the form of a salt with another counter-ion, for example using a suitable ion exchange resin.

Examples of pharmaceutically acceptable addition salts include those derived from mineral acids, such as hydrochloric, hydrobromic, phosphoric, metaphosphoric, nitric and sulphuric acids; from organic acids, such as tartaric, acetic, trifluoroacetic, citric, malic, lactic, fumaric, benzoic, glycolic, gluconic, succinic and arylsulphonic acids; and from metals such as sodium, magnesium, or preferably, potassium and calcium. Particularly preferred salts include those derived from acetic, trifluoroacetic, hydrochloric and tartaric acids.

By "solvate" we mean a solid form wherein the relevant compound (e.g. a compound of formula IA, IB or IC) is associated with one or more solvent molecules. The term solvate includes hydrates and other solvates of pharmaceutically-acceptable solvents. A preferred solvent for solvate formation is DMSO.

By "clathrate" we mean a solid form wherein the relevant compound (e.g. a compound of formula IA, IB or IC) forms a lattice that contains a guest molecule (e.g. a pharmaceutically-acceptable solvent) within the lattice structure.

By "amino acid" and "residue" (for example D-phenylalanine "residue") we mean the dehydrated portion of an amino acid present in polypeptide chains and represented by the following formula
<CHM>
wherein S. represents an amino acid side chain. For the avoidance of doubt, the term "amino acid" includes non-proteinogenic amino acids unless otherwise specified.

By "amino acid side chain" or "side chain of an amino acid" we mean the group attached to the position α to the carboxyl and amino groups in α-amino acids, including non-proteinogenic α-amino acids and particularly proteinogenic amino acids. The skilled person will understand that the most common natural amino acids are known by their trivial names and will be aware of the side chain groups present in these amino acids.

"Proteinogenic" amino acids are the <NUM> amino acids that may be naturally encoded or naturally found in the genetic code of organisms. "Non-proteinogenic" amino acids are those not naturally encoded or found in the genetic code of any organism. The set of non-proteinogenic amino acids is generally considered to include all organic compounds with an amine (-NH<NUM>) and a carboxylic acid (-COOH) functional group linked via a single additional carbon atom, as well as a side chain and a hydrogen bound to that single additional carbon atom, but excluding selenocysteine, pyrrolysine and the <NUM> standard amino acids that are incorporated into proteins during translation. Non-proteinogenic amino acids include those amino acids that are intermediates in biosynthesis, those that are post-translationally formed in proteins, and those that possess a physiological role (e.g. components of bacterial cell walls, neurotransmitters and toxins). References to hydrophobic non-proteinogenic amino acid side chains are references to hydrophobic side chains (particularly those formed primarily of alkyl and/or aryl groups in the absence of polar groups) which are capable of being bound to an amino acid backbone. References to polar non-proteinogenic amino acid side chains are references to polar side chains (particularly those comprising a hydroxyl group or an amide functional group (e.g. wherein one or more of said groups is bound to the amino acid via a linear, branched, cyclic or part cyclic C<NUM>-<NUM> alkylene group)) which are capable of being bound to an amino acid backbone.

Various structural features, such as L<NUM> and Q represent linking groups which form a bridge between two separate portions of the molecule. In each case, such linking groups include -OC(O)-. For L<NUM>, the left-hand hyphen in such linking groups represents the point of attachment to L<NUM>, and the right-hand hyphen in such linking groups represents the point of attachment to L<NUM>. For Q, the left-hand hyphen in such linking groups represents the point of attachment to the alkylene linker that is bound to the carbon atom at R<NUM>, and the right-hand hyphen in such linking groups represents the point of attachment to the alkylene linker that is bound to the carbon atom at R<NUM>.

The delivery agent may be a delivery agent fragment of formula II to X as hereinafter defined, and may be covalently bonded to a compound of formula IA, IB or IC at any position on the molecule. As such, for the avoidance of doubt, a delivery agent may be included in all of the definitions of substituents listed hereinabove and, may also be appended to any other region of the molecule, such as to any one of the amino acid residues AA<NUM> to AA<NUM>. The optimum point of attachment of the delivery agent may be determined by the skilled person.

A preferred point of attachment for the delivery agent is to the N-terminus of the peptide sequence. Thus, in one embodiment, R<NUM> may also be a delivery agent. For compounds of formula IA (and IAA), other preferred points of attachment for the delivery agent include the groups represented by R9a, R10a, and R11a. For compounds of formula IB, other preferred points of attachment for the delivery agent include the groups represented by R9b, R10b, and R11b. For compounds of formula IC, other preferred points of attachment for the delivery agent include the groups represented by R9c, R10c, and R<NUM>.

Unless otherwise specified, alkyl groups and alkoxy groups as defined herein may be straight-chain or, when there is a sufficient number (i.e. a minimum of three) of carbon atoms, be branched-chain and/or cyclic. Further, when there is a sufficient number (i.e. a minimum of four) of carbon atoms, such alkyl and alkoxy groups may also be part cyclic/acyclic. Such alkyl and alkoxy groups may also be saturated or, when there is a sufficient number (i.e. a minimum of two) of carbon atoms, be unsaturated. Unless otherwise specified, alkyl and alkoxy groups may also be substituted with one or more halo, and especially fluoro, atoms.

Unless otherwise specified, alkylene groups as defined herein may be straight-chain or, when there is a sufficient number (i.e. a minimum of two) of carbon atoms, be branched-chain. Such alkylene chains may also be saturated or, when there is a sufficient number (i.e. a minimum of two) of carbon atoms, be unsaturated. Unless otherwise specified, alkylene groups may also be substituted with one or more halo atoms.

The term "aryl", when used herein, includes C<NUM>-<NUM> aryl groups such as phenyl, naphthyl and the like. When substituted, aryl groups are preferably substituted with between one and three substituents.

The term "acyl" as used herein refers to alkyl groups having a carbonyl group attached to the carbon which forms the point of attachment to the rest of the molecule.

When the stereochemistry of a chiral centre is not explicitly defined herein (i.e. by the use of wedged/hashed bonds) it should be understood that the stereocentre may be present in the R- or S-configuration, or a mixture of both configurations.

The skilled person will realise that all references herein to particular aspects of the invention include references to all embodiments and combinations of one or more embodiments that make up that aspect of the invention. Thus, all embodiments of particular aspects of the inventions may be combined with one or more other embodiments of that aspect of the invention to form further embodiments without departing from the teaching of the invention.

In one embodiment of the invention, Z represents -O-. For example, the compound of the invention may be a compound of formula IAA:
<CHM>.

In one embodiment of the invention, particularly when the compound of the invention is a compound of formula IA (or IAA), R10a represents a hydrophobic proteinogenic amino acid side chain, a hydrophobic non-proteinogenic amino acid side chain or hydrogen; optionally wherein R10a represents hydrogen, C<NUM>-<NUM> alkyl, C<NUM>-<NUM> alkylthiomethyl, phenyl, naphthyl, biphenyl, toluyl, toluylmethyl or the side chain of an amino acid selected from the group consisting of valine, isoleucine, leucine, methionine, phenylalanine, tyrosine and tryptophan.

In the compounds of the invention, R10a represents a hydrophobic proteinogenic amino acid side chain, a hydrophobic non-proteinogenic amino acid side chain, hydrogen, or C-R10a may be linked to the adjacent nitrogen atom to form a proline ring (i.e. such that the -N(H)-C(R10a)- fragment in the compounds of formula IA is modified to represent
<CHM>. Suitable amino acid side chains that may be mentioned in the context of R10a include proteinogenic amino acid hydrophobic side chains (such as those of alanine (i.e. a methyl group), valine, isoleucine, leucine, methionine, phenylalanine, tyrosine and tryptophan), non-proteinogenic amino acid hydrophobic side chains (such as C<NUM>-<NUM> alkyl (e.g. ethyl, n-propyl, cyclopropyl, propenyl, n-butyl, tert-butyl, cyclobutyl, butenyl, pentyl, cyclopentyl, hexyl, cyclohexyl, heptyl, or octyl), C<NUM>-<NUM> alkylthiomethyl, phenyl, naphthyl, biphenyl, toluyl, or toluylmethyl), and others (such as glycine and proline). Compounds of formula IA in which the R10a group is hydrogen or preferably a hydrophobic side chain (including either a proteinogenic or non-proteinogenic hydrophobic amino acid side chain) have been found to be surprisingly effective in inhibiting or killing bacteria. Thus, in a preferred embodiment, R10a is a hydrophobic side chain. Most preferably R10a is a hydrophobic side chain in the L-configuration. Particular hydrophobic side chains that may be mentioned include C<NUM>-<NUM> alkyl groups (e.g. methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl, phenyl, hydroxyphenyl, benzyl, indolylmethyl and CH<NUM>SCH<NUM>CH<NUM>-).

In an embodiment of the invention, R<NUM> represents H, C<NUM>-<NUM> alkyl, benzyl, or a delivery agent (e.g. a fragment of formula II to X, as defined hereinafter). Preferably, R<NUM> does not represent a delivery agent fragment of formula II to X, i.e. R<NUM> represents H, C<NUM>-<NUM> alkyl, or benzyl.

In another embodiment, R<NUM> represents a delivery agent fragment of formula II to X as defined hereinafter or, preferably, H, C<NUM>-<NUM> alkyl, or benzyl.

In a further embodiment R<NUM> represents a delivery agent fragment of formula II to X as defined hereinafter or, most preferably, H or methyl.

In a particular embodiment, AA<NUM> represents a hydrophobic proteinogenic amino acid, and AA<NUM> and AA<NUM> each independently represents a proteinogenic amino acid, diaminopropanoic acid, diaminobutanoic acid, or ornithine.

The compounds of the invention are proposed as analogues of Teixobactin. Consequently, it is preferred that the sequence of amino acids represented by AA<NUM> to AA<NUM> is structurally similar to the corresponding amino acid sequence in Teixobactin. Thus, in embodiments of the invention:.

It has been surprisingly found that structural variation is tolerated to a much greater extent at positions represented by AA<NUM>, AA<NUM> and AA<NUM> (as well as R9a, R9b and R9c). Thus, in compounds of the invention, AA<NUM> represents an L-isoleucine residue, AA<NUM> represents a D-allo-isoleucine or D-isoleucine residue, AA<NUM> represents an L-isoleucine residue, and AA<NUM> represents an L-serine residue, whereas AA<NUM>, AA<NUM> and AA<NUM> may be varied as described herein.

Whilst AA<NUM>, AA<NUM> and AA<NUM> preferably represent a D-phenylalanine residue, an L-serine residue and a D-glutamine residue, respectively, i.e. in line with the structure of Teixobactin, other amino acids or similar structures may be substituted at these three positions. For example, AA<NUM> and AA<NUM> may each independently represent any hydrophobic amino acid (including a proteinogenic amino acid (such as alanine, valine, isoleucine, leucine, methionine, phenylalanine, tyrosine or tryptophan) or a non-proteinogenic amino acid (such as norvaline, cyclohexylglycine, cyclohexylalanine, phenylglycine, biphenylglycine, biphenylalanine, naphthylglycine or naphthylalanine)), any polar non-charged amino acid (including a proteinogenic amino acid (such as serine, threonine, asparagine, or glutamine) or a non-proteinogenic amino acid (such as one with a side chain comprising a hydroxy group or an amide functional group bound to the amino acid via a linear, branched, cyclic or part cyclic C<NUM>-<NUM> alkylene group)), any positively charged amino acid, diaminopropanoic acid, diaminobutanoic acid, or ornithine. AA<NUM> may represent any hydrophobic amino acid as described above in respect of AA<NUM> and AA<NUM>. In a particular embodiment, AA<NUM> and AA<NUM> may represent L-arginine or, preferably, L-alanine at either or both of these positions. It is also preferred that, in embodiments in which a delivery agent is covalently bound to the compound of the invention, it is bound to the amino acid at AA<NUM>, AA<NUM> or AA<NUM> (or at R11a, R11b or R11c as is described hereinafter).

In one embodiment, R<NUM> preferably represents hydrogen or a methyl group so as to form part of a serine or threonine residue. The group at R<NUM> may be present in either the R- or S- configuration, though it is preferred that it is present in the S-configuration (for example, so as to form part of a D-threonine residue) when R<NUM> is methyl.

In one embodiment of formula IA and example compounds of formula IB and IC, R9a, R9b, and R9c represent a proteinogenic amino acid side chain, -CH<NUM>-NH<NUM>, -(CH<NUM>)<NUM>-NH<NUM> or -(CH<NUM>)<NUM>-NH<NUM>.

In another embodiment of formula IA and further example compounds of IB and IC, R9a, R9b and R9c preferably represent a hydrophobic proteinogenic or non-proteinogenic amino acid side chain (such as that of alanine (i.e. a methyl group), valine, isoleucine, leucine, methionine, phenylalanine, tyrosine, tryptophan, norvaline, cyclohexylglycine, cyclohexylalanine, phenylglycine, biphenylglycine, biphenylalanine, naphthylglycine or naphthylalanine), a side chain of a positively charged amino acid (such as that of histidine, lysine or arginine), a side chain of a polar non-charged proteinogenic or non-proteinogenic amino acid (such as that of serine, threonine, asparagine, or glutamine, or a hydroxy group or an amide functional group bound to the remainder of the molecule via a linear, branched, cyclic or part cyclic C<NUM>-<NUM> alkylene group) or -CH<NUM>-NH<NUM>, -(CH<NUM>)<NUM>-NH<NUM> or -(CH<NUM>)<NUM>-NH<NUM>. Most preferably, R9a, R9b and R9c represent a hydrophobic amino acid side chain. The groups at R9a, R9b and R9c may be present in either the D- or L- configuration, though it is preferred that it is present in the L-configuration. Thus, for example, when R9a, R9b or R9c represent a methyl group (i.e. the side chain of alanine), the chiral carbon to which R9a, R9b or R9c is bound is preferably in the S-configuration (thus corresponding to the L-alanine that it present at this position for Teixobactin).

In one embodiment, R11a represents a proteinogenic amino acid side chain.

In another embodiment of formula IA or example compounds of formula IC, R11a or R11c represents a hydrophobic proteinogenic or non-proteinogenic amino acid side chain (such as that of alanine (i.e. a methyl group), valine, isoleucine, leucine, methionine, phenylalanine, tyrosine, tryptophan, norvaline, cyclohexylglycine, cyclohexylalanine, phenylglycine, biphenylglycine, biphenylalanine, naphthylglycine or naphthylalanine). The group at R11a or R11c may be present in either the D- or L- configuration, though it is preferred that it is present in the L-configuration. Thus, for example, when R11a or R11c represents a butyl group (e.g. the side chain of isoleucine), the chiral carbon to which R11a or R11c is bound is preferably in the S-configuration (thus corresponding to the L-isoleucine that is present at this position for Teixobactin). It is also preferred that, in embodiments in which a delivery agent is covalently bound to the compound of the invention, that delivery agent is bound to the amino acid side chain at R11a or R11c or the -C(O)NH<NUM> group represented by R11b (or at AA<NUM> or AA<NUM> as is described hereinbefore).

Compounds of formula IB are based on Teixobactin but primarily involve modification, and possibly opening, of the cyclic portion of the macromolecule. Compounds of formula IB have been found to be particularly effective as antibacterial agents.

In compounds of formula IB, R10b may represent the side chain of arginine, lysine, histidine or allo-enduracididine, a -C<NUM>-<NUM> alkyl-NH<NUM> group, a -C<NUM>-<NUM> alkyl-NH-C(=NH)-NH<NUM> group, or any of the preferred groups defined hereinabove in respect of R10a. References herein to the side chain of enduracididine are references the fragment <NUM>-imino-<NUM>-imidazolidinylmethyl. The most preferred structure for R10b is the side chain of arginine (i.e. a -C<NUM> alkyl-NH-C(=NH)-NH<NUM> group).

Thus, in compounds of formula IB, R10b may represent the side chain of arginine, lysine, and histidine or enduracididine, a -C<NUM>-<NUM> alkyl-NH<NUM> group, a -C<NUM>-<NUM> alkyl-NH-C(=NH)-NH<NUM> group, or a fragment of formula -L<NUM>-L<NUM>-L<NUM>-X<NUM> in which each X<NUM> is independently selected from the group consisting of -C(O)-C<NUM>-<NUM> alkyl, -C(O)-NH<NUM>, -C(S)-NH<NUM>, a fragment of formula Q, and a C<NUM>-<NUM> alkyl group substituted by one or more X<NUM> substituents. In a particularly preferred example, X<NUM> represents either a fragment of formula Q, or a C<NUM>-<NUM> alkyl group substituted by one or more (e.g. <NUM>) X<NUM> substituents. In a further preferred example of the invention, X<NUM> represents either a fragment of formula Q, or a C<NUM>-<NUM> (e.g. C<NUM>-<NUM>) alkyl group substituted by at least two X<NUM> substituents (optionally wherein each X<NUM> independently represents -NH<NUM>, -OH, -NHC(O)NH<NUM>, -NHC(S)NH<NUM>, -NHC(=NH)NH<NUM>).

In a further compound of formula IB, a preferred embodiment, R10b may represent the side chain of lysine or, preferably, arginine, or a pendant group which contains at least two terminal guanidinyl, urea, thiourea, amino and/or hydroxyl groups (e.g. at least two X<NUM> groups). For example, R10b may represent -L<NUM>-N(X<NUM>)<NUM> or -L<NUM>-L<NUM>-L<NUM>-C<NUM>-<NUM> alkyl in which said C<NUM>-<NUM> alkyl is substituted by two X<NUM> groups. In another preferred example, R10b represents - C<NUM>-<NUM> lkylene-N(X<NUM>)<NUM> or -C<NUM>-<NUM> alkylene-L<NUM>-C<NUM>-<NUM> alkyl in which said C<NUM>-<NUM> alkyl is substituted by two X<NUM> groups (optionally in which L<NUM> represents -NH-, -NHC(O)-, or -NHC(O)O). In the above-mentioned examples, X<NUM> preferably represents a C<NUM>-<NUM> alkyl group optionally substituted by one or more X<NUM> substituents. Also in such examples (including also those in which X<NUM> represents a C<NUM>-<NUM> alkyl group optionally substituted by one or more X<NUM> substituents), X<NUM> preferably represents a <NUM>- to <NUM>- membered heterocyclyl group (such as pyridine, piperidine, pyrrole or pyrrolidine) or, more preferably, represents -NH<NUM>, -OH, - NHC(O)NH<NUM>, -NHC(S)NH<NUM>, or -NHC(=NH)NH<NUM>.

In examples in which R<NUM> and R<NUM> are not linked, R<NUM> may preferably represent the side chain of an amino acid selected from the list consisting of threonine, cysteine, serine, or lysine; more preferably the side chain of threonine or cysteine; and most preferably the side chain of cysteine. In such examples, both R<NUM> and R<NUM> represents -CH<NUM>-SH.

Preferred groups represented by Q include -OC(O)-, -C(O)O-, -NHC(O)-, -C(O)NH- or -S-S-.

In examples in which R<NUM> and R<NUM> are linked, preferably the alkylene groups in the linking group are linear C<NUM>-<NUM> alkylene groups, which may be the same or different and are optionally substituted with one or more substituents selected from the group consisting of -OH, -SH, -SC<NUM>-<NUM> alkyl, -OC<NUM>-<NUM> alkyl -NH<NUM>, -COOH, -C(O)-NH<NUM>, -COOC<NUM>-<NUM> alkyl and a C<NUM>-<NUM> alkyl group, which latter group (i.e. the C<NUM>-<NUM> alkyl group) is optionally substituted with one or more substituents selected from the list consisting of -OH, -SH, -SC<NUM>-<NUM> alkyl, -NH<NUM>, -COOH, -C(O)-NH<NUM>, -COOC<NUM>-<NUM> alkyl and phenyl.

In further examples, the alkylene groups in the linking group are optionally substituted by one or more substituents selected from the group consisting of -OH, -SH, -SMe, -OMe, - OEt, -NH<NUM>, -COOH, -C(O)-NH<NUM>, -COOMe, COOEt, and a C<NUM>-<NUM> alkyl group, which latter group (i.e. the C<NUM>-<NUM> alkyl group) is optionally substituted with one or more substituents selected from the list consisting of -OH, -SH, -SMe, -NH<NUM>, -COOH, -C(O)-NH<NUM> and -COOMe, - COOEt.

In a further examples, the alkylene groups in the linking group (i.e. the linking group formed when R<NUM> and R<NUM> are linked) are optionally substituted by C<NUM>-<NUM> alkyl groups.

In a particular examples, the alkylene groups in the linking group are C<NUM>-<NUM> alkylene groups, optionally substituted by one or more methyl groups.

In a further disclosure, there is provided a compound of formula IB, wherein the linking group is -CH<NUM>-Q-CH<NUM>-.

In a particular examples Q represents -S-S-.

In a further examples, there is provided a compound of the invention, wherein when R<NUM> and R<NUM> are linked, the linking group is selected from the group consisting of:
<CHM>
wherein the wavy line at the bottom of each structure indicates the point of attachment to the carbon atom at R<NUM> and the wavy line at the top of the structure indicates the point of attachment to the carbon atom at R<NUM>.

In a further examples there is provided a compound of the invention, wherein the cyclic structure comprising the linking group formed by the linkage of R<NUM> and R<NUM> is a <NUM>- to <NUM>-membered ring, for example a <NUM>- to <NUM>-membered ring and preferably a <NUM>-membered ring.

By "[number]-membered ring" (e.g. <NUM>-membered ring), we mean a cyclic structure containing the specified number of ring-constituting atoms, i.e. a ring in which said number represents the number of skeleton atoms forming said ring.

In examples in which the compound is a compound of formula IB,.

In a preferred disclosure, there is provided a compound of formula IB, wherein:.

In still further preferred examples of compounds of formulae IB and IC, AA<NUM> represents an L-isoleucine residue, AA<NUM> represents a D-allo-isoleucine or D-isoleucine residue, AA<NUM> represents an L-isoleucine residue, AA<NUM> represents an L-serine residue, AA<NUM> represents a hydrophobic amino acid, and AA<NUM> and AA<NUM> each independently represent a hydrophobic amino acid, a polar non-charged amino acid, a positively charged amino acid, diaminopropanoic acid, diaminobutanoic acid or ornithine (optionally wherein AA<NUM> represents an L-serine residue and/or AA<NUM> represents a D-glutamine residue), and:.

<CHM>
<CHM>
wherein m represents from <NUM> to <NUM>.

In these compounds of formula IB and IC and in embodiments of formula IA, it is preferred that Z represents -O- and it is most preferred that R<NUM>, R<NUM>, R9a, R9b and R9c each represent methyl, and R11a and R11c represent the side chain of isoleucine.

Preferred compounds of formula IC are those in which:
<CHM>.

Preferably only one of AA<NUM> to AA<NUM>, R9c and R11c contains a group represented by Rc.

It has been found that structural changes can be made at the AA<NUM> and AA<NUM> groups of Teixobactin without significantly reducing the antibacterial efficacy of the resulting compound. Thus, preferred positions at which the mandatory Rc substituent may be located are R9c and R11c, and particularly AA<NUM> and AA<NUM>.

Particular compounds of formula IC that may be mentioned include those in which:.

In compounds (i) to (iii) above, particularly preferred compounds are those in which:.

It is most preferred that the compound of formula IA, IB or IC is not covalently bonded to a delivery agent. However, according to an alternative embodiment, a compound of the invention is covalently bound to a delivery agent which is a fragment of formula II:
<CHM>
wherein D represents a dendrimer fragment to which the X<NUM> groups shown are attached, X<NUM> represents -NH<NUM>, boronic acid or a boronic acid derivative; and n is <NUM> or more (e.g. from <NUM> to <NUM>); and wherein the wavy line indicates the point of attachment to the compound of formula IA, IB or IC.

By "delivery agent" we mean any substance which facilitates the binding of an antibacterial agent to a portion of a bacterial cell (preferably in the region of the bacterial cell wall), and which can thereby anchor the antibacterial agent in the vicinity of the biological target (e.g. an enzyme that is important for cellular activity).

Unless otherwise stated, terms such as "binding", "bound", etc., refer to the interaction between molecules or chemical structures which serve to hold those molecules or chemical structures in close proximity to one another. In the context of the present invention, the term "binding", unless otherwise stated, particularly refers to the binding that occurs as a result of interactions between permanent dipoles or more preferably as a result of hydrogen bonding between the molecular structures involved.

By the phrase "hydrophilic portion which is capable of binding to one or more structures", we include a molecular fragment which is more soluble in water or other polar solvents (e.g. protic solvents such as alcohols) than in oil or other hydrophobic solvents (e.g. hydrocarbons). The phrase specifically includes any structure which is capable of binding to one or more structures in bacterial cell membranes by way of one or more hydrogen bonds and/or electrostatic interactions (i.e. ionic bonds).

Particular delivery agents that may be mentioned include those which are capable of binding to one or more structures on a bacterial cell membrane via the formation of one or more covalent bonds with said structures, via the formation of one or more hydrogen bonds with said structures, or through electrostatic interactions between oppositely charged regions on the delivery agent and the bacterial cell membrane (i.e. a form of ionic bonding). In particular embodiments, the delivery agents are able to bind to the bacterial cell membrane via one or more such covalent bonds, a plurality of hydrogen bonds and/or a plurality of such electrostatic interactions. For example, the delivery agent moiety may be capable of forming <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more separate covalent bonds or hydrogen bonds with said structures, thereby greatly enhancing the extent to which the delivery agent is anchored to the cell wall. Delivery agents which are capable of forming at least <NUM>, at least <NUM>, or at least <NUM> of such linkages (particularly hydrogen bonding linkages) are preferred.

Covalent bonds between the delivery agent and the one or more structures on the bacterial cell membrane may be formed, for example, where the delivery agent comprises a boronic acid component or a pharmaceutically-acceptable salt thereof. Where such boronic acids or boronic acid derivatives are present, covalent bonding may occur between the boron atoms of the delivery agent and <NUM>,<NUM>- and <NUM>,<NUM>-diol groups within the saccharides on the surface of the bacterial cell.

Hydrogen bonds between the delivery agent and the one or more structures on the bacterial cell membrane may be formed through interactions of the delivery agent with saccharides on the surface of the bacterial cell, and particularly with other structures such as phosphate groups or sulphate groups in the lipopolysaccharides or phospholipids of the cell membrane. Functional groups that are capable of participating in hydrogen bonding are well known to the skilled person. Particular functional groups that may be mentioned in this respect include primary amines, amidines (including guanidines) and amides (including ureas), as well as pharmaceutically-acceptable salts thereof. Still further particular functional groups that should be mentioned include primary amines, amidines, guanidines, amides and ureas (and pharmaceutically-acceptable salts thereof).

In embodiments in which the delivery agent binds to the bacterial cell wall by way of one or more electrostatic interactions (optionally in combination with one or more hydrogen bonding interactions), the delivery agent may carry a plurality of positively charged regions. Such positively charged regions are able to interact with the negatively charged phosphate groups that are present in the phospholipids and lipopolysaccharides of the cell membranes. The positively charged regions on the delivery agent may be present due to the delivery agent molecule being provided in the form of a salt, or the delivery agent may exist as a zwitterion under physiological conditions. Accordingly, positive charges may be present as a result of the reaction of a free base form of the delivery agent with an acid to form an acid addition salt. Particular delivery agents that may be mentioned include those which contain a plurality (e.g. at least <NUM>, at least <NUM>, or at least <NUM> charged regions) of such charged regions.

Particular delivery agents that may be mentioned therefore include those which comprise one or more functional groups selected from the list consisting of boronic acids, boronic acid derivatives, primary amines, guanidines, and pharmaceutically-acceptable acid addition salts thereof. For example, the delivery agent may comprise one or more functional groups selected from the list consisting of boronic acids, boronic acid derivatives, primary amines, guanidines, and pharmaceutically-acceptable acid addition salts thereof, and when the delivery agent is a compound of formula II, X<NUM> may represent a boronic acid group, a boronic acid derivative, a primary amine, a guanidine, or a pharmaceutically-acceptable acid addition salt of any such groups.

Where the delivery agent comprises one or more primary amine groups, it is preferred that the delivery agent is provided as an acid addition salt (thus containing one or more -NH<NUM>+ groups). Particular delivery agents that may be mentioned in this respect include delivery agents which are not covalently bonded to the antibacterial agent, and which comprise a polypeptide or a polypeptide derivative, or a pharmaceutically-acceptable salt thereof.

In other embodiments of the invention, the delivery agent comprises a plurality of said functional groups, particularly where the functional groups are intended to interact with the cell membrane via electrostatic or hydrogen bonding interactions. For example, the delivery agent may comprise <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more of said functional groups. Delivery agents which comprise larger numbers of such functional groups are believed to be capable of binding more strongly to the structures in the bacterial cell wall, and thereby improve the antibacterial properties of a compound of formula IA, IB or IC.

In a particular embodiment of the invention, the functional groups are independently selected from the list consisting of boronic acids, boronic acid derivatives, primary amines, amidines, guanidines, amides, ureas, and acid addition salts thereof.

In certain embodiments, the delivery agent comprises a dendrimer-like structure. For example, compounds of formula IA, IB or IC contain a delivery agent of formula II comprising a dendrimer fragment at the position denoted as D. The term "dendrimer" is well known in the art, and refers to structures containing a branching, tree-like architecture. Preferably, such dendrimer structures are generally acyclic (e.g. they do not contain any cyclic structures having more than <NUM> members (i.e. the largest ring structures that may be present in the dendrimers are <NUM>-membered rings such as phenyl groups)) or the dendrimer structure may be completely acyclic. A preferred delivery agent is an organic molecule (or a salt thereof) containing a dendrimer fragment (i.e. a fragment containing multiple, tree-like branches), and each of the branches of that dendrimer fragment may be linked to a relevant functional group. Thus, a single delivery agent may contain a plurality of functional groups capable of binding to a bacterial cell membrane via covalent bonds, hydrogen bonds and/or electrostatic interactions along the lines described above.

Particular delivery agents that may be mentioned include those which contain a dendrimer fragment. For example, delivery agents that may be mentioned include those of formula III:
<CHM>
or a pharmaceutically-acceptable salt thereof, wherein D<NUM> represents a dendrimer fragment to which the NH<NUM> groups shown above are attached; and n1 is <NUM> or more (e.g. from <NUM> to <NUM>), and wherein the wavy line indicates the point of attachment to the compound of formula IA, IB or IC.

Other delivery agents that may be mentioned include those of formula IV and V:
<CHM>
<CHM>
or a pharmaceutically-acceptable salt thereof, wherein D<NUM> and D<NUM> each represent a dendrimer fragment to which the groups shown in parentheses are attached; Y represents O, NH or S; and each n1 is <NUM> or more (e.g. from <NUM> to <NUM>), wherein the wavy line indicates the point of attachment to the compound of formula IA, IB or IC.

Further delivery agents that may be mentioned include those of formulae VI to VIII:
<CHM>
<CHM>
<CHM>
wherein each of D<NUM> to D<NUM> represents a dendrimer fragment to which the groups shown in parentheses are attached; Y represents O, NH or S; each n1 is <NUM> or more (e.g. from <NUM> to <NUM>); m, p, q and r each independently represent from <NUM> to <NUM> (e.g. from <NUM> to <NUM>); R<NUM> represents a C<NUM>-<NUM> alkyl group, and wherein the wavy line indicates the point of attachment to the compound of formula IA, IB or IC.

Dendrimer fragments D<NUM> to D<NUM> may be polyglycerol-based structures or may be dendron-based structures. Particular dendrimer fragments that D<NUM> to D<NUM> (preferably D<NUM> to D<NUM>) may represent include those of formulae A to E:
<CHM>
<CHM>.

For each of the dendrimers of formulae A to E, the single wavy line on the left-hand side of the structures as shown corresponds to the point of attachment to the compound of formula IA, IB or IC. The remaining wavy lines indicate the points of attachment of the plurality of amine-, X- or boronic acid-containing portions of the delivery agent (i.e. the bracketed portions in formulae II to VIII).

In fragments of formulae III to V, particular dendrimer fragments that D<NUM> to D<NUM> may represent include those of formulae A to E as defined above wherein the dendrimer fragments are linked to the plurality of amine-containing portions of the delivery agent (i.e. the bracketed portions in formulae III to V) by way of direct bonds or, preferably, additional linker groups. Additional linker groups that may be mentioned in this respect include ester linkages (i.e. -C(O)-O-), amide linkages (i.e. -C(O)-NH-), sulfonamide linkages (i.e. -S(O)<NUM>-NH-), ether linkages (i.e. -O-), amine linkages (i.e. -N(Rx)- in which Rx represents hydrogen or a C<NUM>-<NUM> alkyl group), a C<NUM>-<NUM> (e.g. C<NUM>-<NUM>) alkylene linkage, or a plurality of such linkages in combination. In compounds of formulae III to V which contain multiple such additional linker groups, the additional linker groups may be the same or different.

Particular preferred delivery agents include:.

Other dendrimer structures will be known to the skilled person. For example, various dendrimers that are known to the skilled person include those disclosed in <NPL>. The disclosures in that document show that such dendrimer compounds may have low toxicities.

Other delivery agents that may be mentioned include those of formulae IXa, IXb, and X:
<CHM>
<CHM>
<CHM>
wherein L<NUM> represents an aliphatic linker (e.g. a C<NUM>-<NUM> alkyl chain); D<NUM> and D<NUM> independently represent a direct bond or a dendrimer fragment to which the boron-containing groups shown are attached; n2 is <NUM> or more (e.g. from <NUM> to <NUM>); and optionally wherein D<NUM> and D<NUM> are attached to the boronic acid portions of the compound of formula IXa and X, or boric acid portions of the compound of formula IXb, via a linker group; and wherein the wavy line indicates the point of attachment to the compound of formula IA, IB or IC.

In embodiments of compounds of formula IA, and disclosed compounds of formula IB or IC containing delivery agent fragments of formula IXa, IXb or X, the dendrimer fragments that are represented by D<NUM> and D<NUM> may be polyglycerol-based structures or dendron-based structures as defined above in respect of dendrimer fragments D<NUM> to D<NUM>. Similarly, particular dendrimer fragments that D<NUM> and D<NUM> may represent include those of formulae A to E as defined above.

In compounds of formula IA, IB or IC containing delivery agent fragments of formula IXa, IXb or X, the linker group that may be present in the delivery agent may comprise one or more groups selected from the list comprising C<NUM>-<NUM> alkyl, -NH-, -O-, -C(O)-O-, and -C(O)-NH- (wherein the amide and ester linkers may each be attached in either of the two possible orientations). For example, the linker group may be a -(CH<NUM>)<NUM>-NH-(CH<NUM>)<NUM>-C(O)-NH- group.

Particular delivery agents that may be mentioned include those which contain a dendrimer fragment. That is, particular delivery agents that may be mentioned include fragments of formulae III, IXa, IXb and X, or pharmaceutically-acceptable salts thereof (e.g. fragments of formulae IV, V, IXa, IXb and X or pharmaceutically-acceptable salts thereof, or most preferably fragments of formulae VI, VII, VIII, IXa, IXb and X or pharmaceutically-acceptable salts thereof).

The delivery agent may also comprise a polypeptide or a polypeptide derivative, or a pharmaceutically-acceptable salt thereof. It is preferred (though not essential) that, when the delivery agent is a polypeptide or polypeptide derivative, or a pharmaceutically-acceptable salt thereof, then the polypeptide contains at least two residues selected from the group consisting of arginine and lysine. The amino acid residues may be provided in their naturally occurring stereochemical configuration (e.g. the L-configuration), or the alternative stereochemical configuration. It is preferred that the amino acid residues are provided in their naturally occurring stereochemical configuration.

In embodiments in which the delivery agent is a polypeptide, a polypeptide derivative or a pharmaceutically-acceptable salt thereof (e.g. a polypeptide, or a pharmaceutically-acceptable salt thereof), preferably the polypeptide contains at most <NUM> (e.g. no more than <NUM>) amino acid residues. Particular polypeptides that may be mentioned include acyclic polypeptides (e.g. acyclic polypeptides containing at most <NUM> amino acid residues). For example, polypeptides of particular interest include those which contain at least four, at least six or at least eight arginine or lysine residues. In all cases, the amino acids that form the polypeptides that may be used in the delivery agents may be in either the D or L forms.

Other polypeptides and polypeptide derivatives of particular interest include compounds containing a sequence of at most <NUM> (e.g. between <NUM> and <NUM>) amino acid residues. Polypeptide derivatives include polypeptide compounds which contain non-peptide moieties at one or both ends of the peptide chain. Alternatively or additionally, polypeptide derivatives include polypeptide compounds in which one or more of the amino acids is optionally provided in a chemically modified form. Examples of such modifications include replacing one or more -NH<NUM> groups on side chains on said amino acids (e.g. the side chains of lysine or arginine) with amides and derivatives thereof (e.g. amides, ureas, thioamides or thioureas).

In further examples of the invention , the polypeptide derivative may consist of from one to six amino acids selected from the group consisting of arginine and lysine, optionally together with a suitable linker to bond the polypeptide derivative to the antibacterial compound of formula IA, IB or IC. Polypeptides and polypeptide derivatives which contain higher positive charge have been found to have increased effectiveness in enhancing the antibacterial potential (i.e. reducing the minimum inhibitory concentration) of existing antibacterial agents when the two agents are provided in combination. Therefore, in a preferred embodiment, the polypeptide or polypeptide derivative is a polypeptide-containing compound that bears a positive charge of at least <NUM> units. Particularly preferred embodiments include those in which the polypeptide or polypeptide derivative is a polypeptide-containing compound that bears a positive charge of at least <NUM> (e.g. at least <NUM>) units.

The positive charge may be nominally determined by counting the number of lysine and arginine amino acids that are present in the polypeptide (each such amino acid providing one unit of positive charge). Other amino acids having side chains that are positively charged may also be mentioned in this respect.

An example of a polypeptide delivery agent that may be mentioned is:
<CHM>.

In a further embodiment, there is provided a compound of the invention, wherein R<NUM> represents a delivery agent of formula II to X as hereinabove defined.

In a further embodiment, the compound of the invention is selected from the group consisting of:
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
and
<CHM>.

The compounds of the invention may be prepared in accordance with techniques known to those skilled in the art, for example as described hereinafter.

Thus, according to a second aspect of the invention there is provided a process for the preparation of a compound of formula IA, which comprises any one of steps (ii), (iii), (v) and (vi) below. Also disclosed, but not claimed is a process for the preparation of a compound of formula IB or IC, which comprises any one of steps (i) to (viii) below:.

The processes described in steps (i) to (viii) are referred to hereinafter as "the processes of the invention".

By "performed on a solid support" we mean that the relevant processes are carried out with the peptide sequence covalently bonded to a solid phase resin (for example a polysterene or polyethylene glycol resin (e.g. a ChemMatrix ® resin)). The point of attachment to the solid phase resin may be at the N-terminus or, preferably at the C-terminus of the peptide sequence or a precursor thereof. The peptide sequence will normally be bound to the resin through either an amide or ester linkage, wherein either the carbonyl portion or amine portion is derived from the C-terminus or N-terminus amino acid residue as appropriate.

The skilled person will be able to determine appropriate solid phase resins for use in the processes of the invention and the most appropriate point of attachment of the resin to the peptide sequence for a given process. Suitable resins include the commercially available resins Rink amide resin and <NUM>-chlorotrityl resin, both of which may be attached to the C-terminus of a peptide sequence, via an amide or ester linkage respectively.

Cleavage of the peptide sequence from Rink amide resin and <NUM>-chlorotrityl resin can be achieved under acidic conditions. Cleavage from Rink amide resin results in a primary amide group at the C-terminus of a peptide sequence, and cleavage from <NUM>-chlorotrityl resin results in the carboxylic acid group being restored at the C-terminus.

For compounds of formula IB in which R<NUM> and R<NUM> are linked and R11b represents -C(O)NH<NUM>, the macrocyclic moiety is typically formed by linkage of two amino acid side chains, which allows the solid phase resin to be attached to the C-terminus of one of the ring-forming amino acid residues and thus for macrocyclisation to be performed prior to cleavage from the solid phase resin. The use of Rink amide resin for the synthesis of these compounds also allows for the cleavage to be performed under the same acidic conditions as deprotection of many commonly-employed protecting groups. Collectively, these factors allow for the highly-efficient synthesis of Teixobactin analogues, which display potent antibacterial activity. The presence of a primary amide group (resulting from the cleavage of the Rink amide resin) on the macrocyclic ring appears to be well-tolerated in terms of biological efficacy, even though such a group is not present in Teixobactin.

In further embodiments of the processes of the invention, any two or more of the deprotections of steps (i), (ii), (iii) may be performed concurrently, and any one or more of these deprotections may also be performed concurrently with the cleavage of step (vii). For example, the global deprotection and cleavage from the solid support of a compound of formula (XIX),
<CHM>
wherein AA<NUM>, AA<NUM>, AA<NUM>, AA<NUM>, R<NUM>, R<NUM>, R<NUM>, R9b, PG<NUM>, PG<NUM> and
<CHM>
are as defined hereinabove.

Protecting groups that may be removed concurrently include alcohol and primary amide protecting groups that can be removed under acidic conditions (for example ether protecting groups (e.g. tert-butyl) and trityl amide protecting groups). These groups may also be removed concurrently with the <NUM>,<NUM>,<NUM>,<NUM>,<NUM>-pentamethyldihydrobenzofurane (Pbf) group for the protecting of guanidinyl groups (drawn explicitly in inter alia formula XIX), and with cleavage of the peptide sequence, or a precursor thereto, from Rink amide or <NUM>-chlorotrityl resin.

With reference to synthetic processes, by "performed concurrently" we mean that the relevant two or more transformations are achieved under a single set of reaction conditions.

Other specific transformation steps that may be employed in the synthesis of compounds of formula IA, IB or IC include:.

Compounds of the invention may be prepared by methods analogous to those listed above, together with those that are known to those skilled in the art. Compounds of formula IA, IB or IC may be prepared using processes involving solid (such as solid-phase peptide synthesis SPPS) or solution phase organic synthesis, as appropriate, using conditions that are known to those skilled in the art.

Persons skilled in the art will appreciate that, in order to obtain compounds of formula IA, IB or IC (etc.) in an alternative, and, on some occasions, more convenient, manner, the individual process steps mentioned hereinbefore may be performed in a different order, and/or the individual reactions may be performed at a different stage in the overall route (i.e. substituents may be added to and/or chemical transformations performed upon, different intermediates to those mentioned hereinbefore in conjunction with a particular reaction). This may negate, or render necessary, the need for protecting groups.

The type of chemistry involved will dictate the need, and type, of protecting groups as well as the sequence for accomplishing the synthesis and whether each step should be performed in solution or on solid phase. A recent review of suitable protecting groups for amino acids is provided by <NPL>.

Advantageously, removal of protecting groups and cleavage from solid phase resins should be performed towards the end (preferably as the final step) of a synthetic route in order to maximise the efficiency of a synthetic process.

The compounds of the invention are useful because they possess pharmacological activity. They are therefore indicated as pharmaceuticals.

Thus, according to a third aspect of the invention there is provided a pharmaceutical composition comprising a compound of the invention in combination with a pharmaceutically-acceptable adjuvant diluent or carrier. Such formulations are referred to hereinafter as the "formulations of the invention".

According to a fourth aspect of the invention, there is provided the compounds of the invention or the formulations of the invention for use in medicine.

The use of compounds or formulations of the invention in medicine includes their use as pharmaceuticals (both for human and veterinary use). The compositions of the present invention may also be useful in other fields of industry. For example, the compositions may be useful as plant protection products (i.e. in agriculture), in cosmetic products (e.g. in creams, toothpaste, lotions and ointments), and hygiene and sterilisation procedures (e.g. in scientific laboratories).

In this respect, fifth, sixth, seventh and eighth aspects of the invention provide, respectively:.

When used herein, the terms "bacteria" (and derivatives thereof, such as "bacterial infection") includes references to organisms (or infections due to organisms) of the following classes and specific types:.

Thus, compounds of the invention may be used to kill any of the above-mentioned bacterial organisms.

Particular bacteria that may be mentioned in this respect include:.

The compounds of the present invention are particularly advantageous as, when covalently bonded to a delivery agent, they are capable of inhibiting the growth, survival and reproduction of Gram negative bacteria, something which few existing antibacterial agents are able to do effectively. Thus, in particular embodiments of all of the methods disclosed herein, the bacteria are Gram negative bacteria.

In this respect, particular conditions that the compounds and formulations of the invention can be used to treat include tuberculosis (e.g. pulmonary tuberculosis, non-pulmonary tuberculosis (such as tuberculosis lymph glands, genito-urinary tuberculosis, tuberculosis of bone and joints, tuberculosis meningitis) and miliary tuberculosis), anthrax, abscesses, acne vulgaris, actinomycosis, bacilliary dysentry, bacterial conjunctivitis, bacterial keratitis, botulism, Buruli ulcer, bone and joint infections, bronchitis (acute or chronic), brucellosis, burn wounds, cat scratch fever, cellulitis, chancroid, cholangitis, cholecystitis, cutaneous diphtheria, cystic fibrosis, cystitis, diffuse panbronchiolitis, diphtheria, dental caries, diseases of the upper respiratory tract, empymea, endocarditis, endometritis, enteric fever, enteritis, epididymitis, epiglottitis, erysipclas, erysipeloid, erythrasma, eye infections, furuncles, Gardnerella vaginitis, gastrointestinal infections (gastroenteritis), genital infections, gingivitis, gonorrhoea, granuloma inguinale, Haverhill fever, infected burns, infections following dental operations, infections in the oral region, infections associated with prostheses, intraabdominal abscesses, Legionnaire's disease, leprosy, leptospirosis, listeriosis, liver abscesses, Lyme disease, lymphogranuloma venerium, mastitis, mastoiditis, meningitis and infections of the nervous system, mycetoma, nocardiosis (e.g. Madura foot), non-specific urethritis, opthalmia (e.g. opthalmia neonatorum), osteomyelitis, otitis (e.g. otitis externa and otitis media), orchitis, pancreatitis, paronychia, pelveoperitonitis, peritonitis, peritonitis with appendicitis, pharyngitis, phlegmons, pinta, plague, pleural effusion, pneumonia, postoperative wound infections, postoperative gas gangrene, prostatitis, pseudo-membranous colitis, psittacosis, pulmonary emphysema, pyelonephritis, pyoderma (e.g. impetigo), Q fever, rat-bite fever, reticulosis, Ritter's disease, salmonellosis, salpingitis, septic arthritis, septic infections, septicameia, sinusitis, skin infections (e.g. skin granulomas), syphilis, systemic infections, tonsillitis, toxic shock syndrome, trachoma, tularaemia, typhoid, typhus (e.g. epidemic typhus, murine typhus, scrub typhus and spotted fever), urethritis, wound infections, yaws, aspergillosis, candidiasis (e.g. oropharyngeal candidiasis, vaginal candidiasis or balanitis), cryptococcosis, favus, histoplasmosis, intertrigo, mucormycosis, tinea (e.g. tinea corporis, tinea capitis, tinea cruris, tinea pedis and tinea unguium), onychomycosis, pityriasis versicolor, ringworm and sporotrichosis.

Further conditions that may be mentioned in this respect include infections with MSSA, MRSA, Staph. epidermidis, Strept. agalactiae, Strept. pyogenes, Escherichia coli, Klebs. pneumoniae, Klebs. oxytoca, Pr. mirabilis, Pr. rettgeri, Pr. vulgaris, Haemophilis influenzae, Enterococcus faecalis or Enterococcus faecium.

The compounds and formulations of the invention will normally be administered orally, subcutaneously, intravenously, intraarterially, transdermally, intranasally, by inhalation, or by any other parenteral route, in the form of pharmaceutical preparations comprising the active ingredient either as a free base or a non-toxic organic or inorganic acid addition salt, in a pharmaceutically acceptable dosage form. Depending upon the disorder and patient to be treated, as well as the route of administration, the compounds and formulations may be administered at varying doses.

Suitable daily doses for the compounds and formulations of the invention in therapeutic treatment of humans are in the range of about <NUM> to about <NUM>/m<NUM>.

The most effective mode of administration and dosage regimen for the compounds and formulations of the invention depends on several factors, including the particular condition being treated, the extent and localisation of that condition in the patient being treated, as well as the patient's state of health and their reaction to the compound being administered. Accordingly, the dosages of the compounds and formulations of the invention should be adjusted to suit the individual patient. Methods for determining the appropriate dose for an individual patient will be known to those skilled in the art.

Additionally, compositions of the invention may have the advantage that they may be more efficacious than, be less toxic than, have a broader range of activity than, be more potent than, produce fewer side effects than, or have other useful pharmacological properties over compositions known in the prior art. In particular, compositions of the invention may have the advantage that they are less toxic than compositions known in the prior art due to a reduction in the detrimental effects that the delivery agents may have on cell membrane (of the host organisms).

The use of certain compounds and formulations of the invention in medicine is, to the knowledge of the inventors, novel. In certain embodiments of the invention, the subject of the treatment or prevention methods is a mammal, particularly a human.

The invention is illustrated by the following examples in which:.

The invention will now be described in more detail by reference to the following non-limiting Examples.

For MIC testing all peptides were dissolved in DMSO (according to the method of <NPL>). Bacteria were grown on Mueller Hinton broth (oxoid). All incubations were at <NUM>. Dilutions were carried out using Mueller Hinton. <NUM>µl of autoclaved Mueller Hinton broth was added to wells <NUM>-<NUM> on a <NUM>-well plate. <NUM>µl of the peptide was added to well one at a concentration of <NUM>µg/ml. 100µl of peptide in well one was taken up and pipetted into well two. The mixture was then mixed via pipetting before 100µl was taken up and pipetted into well three. This process was repeated up to well <NUM>. Once peptide was added to well <NUM><NUM>µl was taken up and then discarded ensuring the well <NUM> had no peptide present. Each well was then inoculated with 100µl of bacteria that had been diluted to an OD600nm of <NUM>. This was repeated three times. The <NUM>-well plates were then incubated for <NUM> hours. The MIC was determined to be the lowest concentration at which there was no growth visible. Results are tabulated in the Examples.

Fmoc-D-Ile-OH, Fmoc-D-Thr(Trt)-OH, Fmoc-<NUM>-Ahx-OH and oxyma pure were purchased from Merck Millipore. All L Amino acids, <NUM>-[Bis(dimethylamino)methylene]-<NUM>-<NUM>,<NUM>,<NUM>-triazolo[<NUM>,<NUM>-b]pyridinium <NUM>-oxid hexafluorophosphate (HATU), Fmoc-D-Gln(Trt)-OH, Boc-D-Nmethylphenyl-OH, Fmoc-D-Thr-OH, Boc-Asp(OtBu)-OH, Fmoc-Glu(OAlI)-OH, Fmoc-Lys(Alloc)-OH, Bis-Boc-pyrazolocarboxamidine, Diisoproplycarbodiimide and Triisopropylsilane were purchased from Fluorochem.

The protecting groups for the amino acids are tBu for Glu, Boc for Pro, Tyr, Lys, Trp, Pbf for Arg and Trt for Gln unless specified otherwise. Diisopropylethylamine, supplied as extra dry, redistilled, <NUM>% pure, was purchased from Sigma Aldrich. Dimethylformamide (DMF) peptide synthesis grade and Trifluoroacetic acid (TFA) was purchased from Rathburn chemicals.

Petroleum ether, Diethyl ether, i-PrOH, MeOH (HPLC grade), and Acetonitrile (HPLC grade) were purchased from Fisher Scientific. Water with the Milli-Q grade standard was obtained in-house from an ELGA Purelab Flex system. <NUM>-Chlorotritylchloride resin (manufacturer's loading: <NUM> mmol/g) was obtained from Fluorochem. Rink amide Chemmatrix resin (manufacturer's loading = <NUM> mmol/g) was obtained from Biotage. All chemicals were used without further purification.

Peptide syntheses were performed using standard Fmoc Solid Phase Peptide Synthesis (SPPS) protocols on a <NUM>-Chlorotritylchloride resin, loading = <NUM> mmol/g or a Rink Amide Chemmatrix Resin, loading = <NUM> mmol/g using a Biotage Initiator + Alstra fully automated microwave peptide synthesizer. All amino acid couplings were performed using <NUM> eq. Amino Acid with <NUM> eq. DIC/Oxyma in DMF as a coupling cocktail by irradiating at <NUM> for <NUM>. Fmoc deprotection was performed using <NUM>% piperidine in DMF.

Peptide cleavage was performed using TFA/TIS/H<NUM>O = <NUM>:<NUM>:<NUM> (<NUM>/<NUM> resin) for <NUM>. Peptides were precipitated using cold Et<NUM>O (-<NUM>) by adding approximately 5x volume of the TFA used for cleavage and centrifuging at <NUM> rpm at <NUM>.

All peptides/conjugates were analysed on a Thermo Scientific Dionex Ultimate <NUM> RP-HPLC equipped with a Phenomenex Gemini NX C18 <NUM>Å (<NUM> x <NUM>) column using the following buffer systems: A: <NUM>% HCOOH in milliQ water. B: MeCN using a flow rate of <NUM>/min. The column was flushed with <NUM>% A for <NUM> prior to an injection and was flushed for <NUM> with <NUM>% B and <NUM>% A after the run was finished.

Peptides were analysed using the following gradient: <NUM>% A for <NUM>. <NUM>-<NUM>% B in <NUM>. <NUM>% B for <NUM>. <NUM>% A for <NUM>.

Peptides and conjugates were purified using the same gradient as mentioned above, on a Thermo Scientific Dionex Ultimate <NUM> RP-HPLC with a flow rate of <NUM>/min using a Phenomenex Gemini NX C18 <NUM>Å (<NUM> x <NUM>) semi-prep column.

Synthesis of Compounds <NUM>, <NUM> & <NUM>: a. Fmoc-AA(PG)-OH (AA = amino acid, PG = protecting group), DIC/Oxyma microwave couplings followed by <NUM>% piperidine in DMF. TFA:TIS:H<NUM>O = <NUM>:<NUM>:<NUM>, <NUM>. c: DMSO:mQ = <NUM>:<NUM> (peptide concentration <NUM>) in air, <NUM>.

Steps a and b. Commercially available Rink amide Chemmatrix resin (manufacturer's loading = <NUM> mmol/g) was swelled in DMF and through automated standard SPPS Compound <NUM> was synthesized using the general procedure described hereinabove.

Crude Compound <NUM> was then dissolved in DMSO:mQ water = <NUM>:<NUM> while maintaining a peptide concentration of <NUM> and was stirred for <NUM> at r. in air to yield Compounds <NUM> (~<NUM>%) & <NUM> (~<NUM>%). Compounds <NUM> and <NUM> were purified using semi-prep RP-HPLC using the protocols described hereinabove.

Synthesis of Compound <NUM>: a. Fmoc-AA(PG)-OH (AA = amino acid, PG = protecting group), HATU/DIPEA followed by <NUM>% piperidine in DMF. [Pd(PPh<NUM>)<NUM>]<NUM> (<NUM> eq. ) + <NUM> eq. PhSiH<NUM> in DCM, <NUM> × <NUM>. <NUM> x <NUM> TFA:TIS:DCM = <NUM>:<NUM>:<NUM>. DIC/<NUM> eq. DMAP in DMF, overnight. Fmoc-AA(PG)-OH (AA = amino acid, PG = protecting group), DIC/Oxyma microwave couplings followed by <NUM>% piperidine in DMF. TFA:TIS:H<NUM>O = <NUM>:<NUM>:<NUM>, <NUM>.

Commercially available Rink amide Chemmatrix resin (manufacturer's loading = <NUM> mmol/g) was swelled in DMF and through automated standard SPPS residues Fmoc-Glu(OAlI)-OH, Fmoc-Arg(Pbf)-OH, Fmoc-Ala-OH and Fmoc-D-Thr(Trt)-OH were coupled in succession using the general protocol described hereinabove.

The Allyl protecting group of Glu was removed using <NUM> eq. [Pd(PPh<NUM>)]<NUM> and <NUM> eq. PhSiH<NUM> in dry DCM under argon for <NUM>. This procedure was repeated twice and the resin was washed thoroughly with DCM and DMF to remove any Pd stuck to the resin.

The resin was swelled in DCM. The Trt protecting group of Thr was then removed using 24x30s bursts of <NUM>% TFA + <NUM>% TIS in DCM.

Esterification was performed using <NUM> eq. DIC + <NUM> eq. DMAP in DMF by shaking the resin overnight.

The subsequent amino acids were coupled using the protocols described hereinabove.

Cleavage, precipitation and HPLC purification were performed using the protocols described hereinabove (<NUM>% overall recovery after HPLC purification).

Synthesis of Compound <NUM>: a. Fmoc-AA(PG)-OH (AA = amino acid, PG = protecting group), HATU/DIPEA followed by <NUM>% piperidine in DMF. [Pd(PPh<NUM>)<NUM>]<NUM> (<NUM> eq. ) + <NUM> eq. PhSiH<NUM> in DCM, <NUM> x <NUM>. HATU/<NUM> eq. DIPEA, overnight. Fmoc-AA(PG)-OH (AA = amino acid, PG = protecting group), DIC/Oxyma microwave couplings followed by <NUM>% piperidine in DMF. TFA:TIS:H<NUM>O = <NUM>:<NUM>:<NUM>, <NUM>.

Commercially available Rink amide Chemmatrix resin (manufacturer's loading = <NUM> mmol/g) was swelled in DMF and through automated standard SPPS residues Fmoc-Glu(OAlI)-OH, Fmoc-Arg(Pbf)-OH, Fmoc-Ala-OH and Fmoc-Lys(Alloc)-OH were coupled in succession using the general protocols described hereinabove.

The Allyl protecting group of Glu and the Alloc protecting group of Lys were removed using <NUM> eq. [Pd(PPh<NUM>)]<NUM> and <NUM> eq. PhSiH<NUM> in dry DCM under argon for <NUM>. This procedure was repeated twice and the resin was washed thoroughly with DCM and DMF to remove any Pd stuck to the resin.

Amide bond formation was performed using <NUM> eq. of HATU with <NUM> eq. of DIPEA in DMF by shaking the resin overnight.

The subsequent amino acids were coupled using the general protocols described hereinabove.

Cleavage, precipitation and HPLC purification were performed using the general protocols described hereinabove (<NUM>% overall recovery after purification).

Synthesis of Compound <NUM>: a. Fmoc-Ala-OH/<NUM> eq. DIPEA in DCM, <NUM>. <NUM>% piperidine in DMF followed by <NUM> eq. AllocHN-D-Thr-OH, <NUM> eq. HATU/<NUM> eq. Fmoc-Ile-OH, <NUM> eq. DIC, <NUM> mol% DMAP in DMF, <NUM> followed by capping with Ac<NUM>O/DIPEA <NUM>% in DMF d. Fmoc-Arg(Pbf)-OH, <NUM> eq. HATU/<NUM> eq. DIPEA in DMF, <NUM> followed by <NUM>% piperidine in DMF e. Trt-Cl, <NUM>% Et<NUM>N in DCM, <NUM>. [Pd(PPh<NUM>)<NUM>]<NUM> (<NUM> eq. ) + <NUM> eq. PhSiH<NUM> in DCM, <NUM> × <NUM>. Fmoc-AA(PG)-OH (AA = amino acid, PG = protecting group), HATU/DIPEA followed by <NUM>% piperidine in DMF. TFA:TIS:DCM = <NUM>:<NUM>:<NUM>, <NUM>. HATU/<NUM> eq. DIPEA in DMF, <NUM>, monitored on HPLC. TFA:TIS:H<NUM>O = <NUM>:<NUM>:<NUM>, <NUM>.

Commercially available <NUM>-Chlorotrityl chloride resin (manufacturer's loading = <NUM> mmol/g) was swelled in DCM in a reactor. To this resin was added <NUM> eq. Fmoc-Ala-OH/<NUM> eq. DIPEA in DCM and the reactor was shaken for <NUM>. The loading determined by UV absorption of the piperidine-dibenzofulvene adduct was calculated to be <NUM> mmol/g.

The fmoc protecting group was removed using <NUM>% piperidine in DMF following the general procedure described hereinabove above. AllocHN-D-Thr-OH was then coupled to the resin by adding <NUM> eq. of the AA, <NUM> eq. HATU and <NUM> eq. DIPEA in DMF and shaking for <NUM> at r.

Esterification was performed using <NUM> eq. of Fmoc-Ile-OH, <NUM> eq. DIC and <NUM> mol% DMAP in DCM and shaking the reaction for <NUM>. This was followed by capping the unreacted alcohol using <NUM>% Ac<NUM>O/DIPEA in DMF and shaking for <NUM>.

Fmoc-Arg(Pbf)-OH was coupled using <NUM> eq. of AA, <NUM> eq. HATU and <NUM> eq. DIPEA in DMF and shaking for <NUM> followed by Fmoc deprotection using <NUM>% piperidine in DMF as described in the general protocols hereinabove.

The N terminus of Arg was protected using <NUM> eq. Trt-Cl and <NUM>% Et<NUM>N in DCM and shaking for <NUM>. The protection was verified by the Ninhydrin colour test.

The Alloc protecting group of D-Thr was removed using <NUM> eq. [Pd(PPh<NUM>)]<NUM> and <NUM> eq. PhSiH<NUM> in dry DCM under argon for <NUM>. This procedure was repeated twice and the resin was washed thoroughly with DCM and DMF to remove any Pd stuck to the resin.

All amino acids were coupled using <NUM> eq. AA, <NUM> eq. HATU and <NUM> eq. Deprotection cycles were performed using the general protocol described hereinabove. Each coupling and deprotection cycle were checked by the Ninhydrin colour test.

The peptide was cleaved off from the resin without cleaving off the protecting groups for the amino acid side chains using TFA:TIS:DCM = <NUM>:<NUM>:<NUM> and shaking for <NUM>.

The solvent was evaporated and the peptide was redissolved in DMF to which <NUM> eq. HATU and <NUM> eq. DIPEA were added and the reaction was stirred for <NUM> to perform the cyclization. The reaction was monitored on HPLC till all starting material had been consumed.

The side-chain protecting groups were then cleaved off using TFA:TIS:H<NUM>O = <NUM>:<NUM>:<NUM> by stirring for <NUM>. The peptide was precipitated using cold Et<NUM>O (-<NUM>) and centrifuging at <NUM> rpm to obtain the crude white solid (<NUM>% overall yield, <NUM>% purity). HPLC purification yielded the compound also as a white solid (<NUM>% recovery, <NUM>% overall yield).

LC-MS data for Compounds <NUM> to <NUM> and Reference Compound <NUM> were collected on an Agilent <NUM> Series instrument with a Phenomenex Kinetex C18 100Å column (<NUM> x <NUM>, <NUM> at <NUM>) connected to an ESMSD type VL mass detector with a flow rate of <NUM>/min was used with the following solvent systems: (A): <NUM>% HCOOH in H<NUM>O and (B) MeCN. The column was flushed with <NUM>% A for <NUM>, then a gradient from <NUM> to <NUM>% B over <NUM> was used, followed by <NUM> of flushing with <NUM>% B. Results are shown in Table <NUM>.

Minimum inhibitory concentrations for various compounds against S. aureus are shown in Table <NUM>.

The general synthesis of Teixobactin derivatives in which the amino acid at position <NUM> (the L-allo-enduracididine amino acid) is replaced with another amino acid is detailed in Example <NUM>, and is described in <NPL>.

Compounds <NUM> to <NUM> (including Reference Compound <NUM>-<NUM> and <NUM>) were prepared by methods analogous to that method. Compounds <NUM> to <NUM> form a series of alanine derivatives of Teixobactin.

The structures of compounds <NUM> to <NUM> (including Reference Compound <NUM>-<NUM> and <NUM>) are, respectively, as follows:
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

LC-MS data were collected on an Agilent <NUM> Series instrument with a Phenomenex Kinetex C18 100Å column (<NUM> x <NUM>, <NUM> at <NUM>) connected to an ESMSD type VL mass detector with a flow rate of <NUM>/min was used with the following solvent systems: (A): <NUM>% HCOOH in H<NUM>O and (B) MeCN. The column was flushed with <NUM>% A for <NUM>, then a gradient from <NUM> to <NUM>% B over <NUM> was used, followed by <NUM> of flushing with <NUM>% B. Results are shown in Table <NUM>.

Minimum inhibitory concentrations for various compounds against MRSA are shown in Table 4A.

We have performed an alanine scan of the Arg<NUM>-teixobactin analogue via the synthesis of <NUM> analogues. The studies reveal that replacement of residues D-NMe-Phe<NUM>, L-Ile<NUM>, D-allo-Ile<NUM>, L-Ile<NUM> and L-Ser<NUM> with Alanine (Compounds <NUM>, <NUM>, <NUM> and <NUM> and Reference Compound <NUM>) results in a significant loss in antibacterial activity. However, the replacement of L-Ser<NUM> and D-Gln<NUM> with L-Ala and D-Ala respectively (Compounds <NUM> and <NUM>) results in a comparable MIC value as that of the Arg<NUM>-teixobactin analogue (Reference Compound <NUM>). Contrary to the current understanding, we further observe that replacing the Arg<NUM> residue with non-polar residues such as Ile and Leu results in analogues which give exceptionally high biological activity, identical to that of Teixobactin against MRSA. Importantly, both Leu<NUM>-teixobactin (Compound <NUM>) and Ile<NUM>-teixobactin (Compound <NUM>) are made up of commercially available simpler building blocks rather than the synthetically challenging enduracididine. It thus seems that the presence of an amino acid with a cationic side chain such as enduracididine, arginine or lysine is not essential for biological activity. NMR studies have also revealed that the mutants S3A, Q4A and R10A (Compounds <NUM>, <NUM> and <NUM>) are more unstructured towards the N-termini but highly structured towards the C termini due to the close-by ring. Surprisingly, Gly<NUM>-teixobactin (Compound <NUM>) shows identical activity to Arg<NUM>-teixobactin (Reference Compound <NUM>) proving that a complete removal of the chiral center at position <NUM> is tolerated provided the configuration of the remaining residues is intact.

Compounds <NUM>, <NUM>, <NUM> and <NUM>, along with Arg<NUM>-teixobactin and vancomycin/daptomycin as controls, were tested against an extended panel of Gram positive bacteria (Table 4B) to provide a more comprehensive overview of the biological activity of these molecules.

The diamino linker was synthesized for Diamino<NUM>-Teixobactin using the procedure below.

<NUM>,<NUM>-diaminopropan-<NUM>-ol (<NUM>, <NUM>. 22mmols) was dissolved in <NUM> methanol and triethylamine (<NUM>) was added dropwise. Boc anhydride (3eq) was then added and heated at <NUM> for <NUM> and 1hr at room temperature. This was monitored by TLC (<NUM>:<NUM>) DCM:methanol. After completion saturated solution of NaHCO<NUM> was added (<NUM>) and extracted with ethyl acetate. The solvent was evaporated in vacuo and used in the next step without purification.

Di-tert-butyl (<NUM>-hydroxypropane-<NUM>,<NUM>-diyl)dicarbamate (<NUM>, <NUM>. 76mmols) was dissolved in <NUM> acetonitrile. N-succinimidyl carbonate (DSC) (<NUM>, <NUM>. 52mmols) was added and dropwise addition of trimethylamine (<NUM>, <NUM>. 28mmols) was added leaving the reaction to stir overnight. After completion of the reaction, the solvent was evaporated and purified on silica with DCM:methanol (<NUM>:<NUM>) to achieve di-tert-butyl (<NUM>-((((<NUM>,<NUM>-dioxopyrrolidin-<NUM>-yl)oxy)carbonyl)oxy)propane-<NUM>,<NUM>-diyl)dicarbamate, <NUM>% yield. The compound was characterized by mass spectrometry.

Lys<NUM>-Teixobactin was synthesised using protocols described in <NPL>. Lys<NUM>-Teixobactin (<NUM>, <NUM>. 0041mmols) was dissolved in 100µL of DMSO and 75µL of Dipea was added. Di-tert-butyl (<NUM>-((((<NUM>,<NUM>-dioxopyrrolidin-<NUM>-yl)oxy)carbonyl)oxy)propane-<NUM>,<NUM>-diyl)dicarbamate (<NUM>, <NUM> mmols) was dissolved in 50µl and added to the Lys<NUM>-Teixobactin solution. This was stirred for <NUM> and then quenched with acetic acid 100µl and monitored by HPLC. This was then purified by reverse phase and freeze dried to yield the BOC protected compound.

To Boc-diamino<NUM>-Teixobactin was added neat formic acid and allowed to stir for 1hr monitoring by HPLC. Water was then added and freeze dried to yield the Teixobactin diamino compound (Compound <NUM>). The compound was characterized by mass spectrometry Exact Mass <NUM> Mass found [M+H+] <NUM>.

To a mixture of <NUM> (<NUM> mmol) of thiourea and <NUM> of <NUM>% aqueous formaldehyde (<NUM> mmol) was added at vigorous stirring <NUM> mmol of glycine/Gamma amino butyric acid/<NUM>-Aminohexanoic acid, and stirring was continued for another <NUM> until it dissolved. The reaction was then left standing at room temperature. A day later, the precipitate was filtered off and recrystallized from a mixture of <NUM>-propanol-water (<NUM>:<NUM>). Yields: <NUM>-<NUM>%.

To <NUM> eq. Thiourea derivative (<NUM>) dissolved in <NUM>µL of DMF <NUM> eq. HOSu (N-hydroxysuccinimide) and <NUM> eq. of DCC was added and stirred for <NUM> hrs until precipitation of cyclohexyl urea was complete. The precipitate was filtered off and discarded.

Lys<NUM>-Teixobactin was synthesized using our previously described procedure (<NPL>)). Lys<NUM>-Teixobactin (<NUM>, <NUM> mmol) was dissolved in <NUM>µL of DMSO and <NUM>µL of DIPEA was added. <NUM>µL of activated thiourea prepared as described above was added to the solution. This was stirred for <NUM> and then acetonitrile was added dropwise until the solution was clear. The reaction mixture was analysed on RP-HPLC followed by RP-HPLC purification and freeze dried to yield the thiourea-containing Teixobactin derivatives (Compounds <NUM> to <NUM>).

Compounds <NUM> to <NUM> are variants of Teixobactin in which the amino acid at position <NUM> is replaced with leucine, isoleucine, cyclohexylglycine, norvaline, phenylalanine or alanine, and from none to three of the amino acids at positions <NUM>, <NUM> and <NUM> are replaced with arginine. These compounds were prepared by methods analogous to the method in Example <NUM>. A detailed method for Compound <NUM> is provided in Example <NUM>.

The structures of compounds <NUM> to <NUM> are, respectively, as follows:
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

Synthesis of D-Arg<NUM>-Leu<NUM>-teixobactin (Compound <NUM>) starting from <NUM>-chlorotritylchloride resin: a. Fmoc-Ala-OH/<NUM> eq. DIPEA in DCM, <NUM>. <NUM>% piperidine in DMF followed by <NUM> eq. AllocHN-D-Thr-OH, <NUM> eq. HATU/<NUM> eq. DIPEA, <NUM> c. Fmoc-Ile-OH, <NUM> eq. DIC, <NUM> mol% DMAP in DCM, <NUM> followed by capping with Ac<NUM>O/DIPEA <NUM>% in DMF, <NUM>% piperidine in DMF d. Fmoc-Leu-OH, <NUM> eq. HATU/<NUM> eq. DIPEA in DMF, <NUM> followed by <NUM>% piperidine in DMF e. Trt-Cl, <NUM>% Et<NUM>N in DCM, <NUM>. [Pd(PPh<NUM>)<NUM>]<NUM> + <NUM> eq. PhSiH<NUM> in dry DCM, <NUM> x <NUM>, <NUM> x <NUM>. Fmoc/Boc-AA(PG)-OH (AA = amino acid, PG = protecting group), <NUM> eq. DIC/Oxyma (µwave, <NUM>) followed by <NUM>% piperidine in DMF (<NUM>, <NUM>). TFA:TIS:DCM = <NUM>:<NUM>:<NUM>, <NUM>. HATU/<NUM> eq. DIPEA in DMF, <NUM>. TFA:TIS:H<NUM>O = <NUM>:<NUM>:<NUM>, <NUM>.

Commercially available <NUM>-chlorotrityl chloride resin (manufacturer's loading = <NUM> mmol/g, <NUM> resin) was swelled in DCM in a reactor. To this resin was added <NUM> eq. Fmoc-Ala-OH/<NUM> eq. DIPEA in DCM and the reactor was shaken for <NUM>. The loading determined by UV absorption of the piperidine-dibenzofulvene adduct was calculated to be <NUM> mmol/g, (<NUM> resin, <NUM> mmol). Any unreacted resin was capped with MeOH:DIPEA:DCM = <NUM>:<NUM>:<NUM> by shaking for <NUM>.

The Fmoc protecting group was deprotected using <NUM>% piperidine in DMF by shaking for <NUM>, followed by draining and shaking again with <NUM>% piperidine in DMF for <NUM>. AlIocHN-D-Thr-OH was then coupled to the resin by adding <NUM> eq. of the AA, <NUM> eq. HATU and <NUM> eq. DIPEA in DMF and shaking for <NUM> at room temperature.

Esterification was performed using <NUM> eq. of Fmoc-Ile-OH, <NUM> eq. DIC and <NUM> mol% DMAP in DCM and shaking the reaction for <NUM>. This was followed by capping the unreacted alcohol using <NUM>% Ac<NUM>O/DIPEA in DMF shaking for <NUM> and Fmoc was removed using protocol described earlier in step (b).

Fmoc-Leu-OH was coupled using <NUM> eq. of AA, <NUM> eq. HATU and <NUM> eq. DIPEA in DMF and shaking for <NUM> followed by Fmoc deprotection using <NUM>% piperidine in DMF as described earlier.

The N terminus of Leu was protected using <NUM> eq. Trt-Cl and <NUM>% Et<NUM>N in DCM and shaking for <NUM>. The protection was verified by the Ninhydrin colour test.

The Alloc protecting group of D-Thr was removed using <NUM> eq. [Pd(PPh<NUM>)]<NUM> and <NUM> eq. PhSiH<NUM> in dry DCM under argon for <NUM>. This procedure was repeated again increasing the time to <NUM> and the resin was washed thoroughly with DCM and DMF to remove any Pd stuck to the resin.

All amino acids were coupled using <NUM> eq. Amino Acid, <NUM> eq. DIC/Oxyma using a microwave peptide synthesizer. Coupling time was <NUM>. Deprotection cycles were performed as described earlier.

The peptide was cleaved from the resin without cleaving off the protecting groups of the amino acid side chains using TFA:TIS:DCM = <NUM>:<NUM>:<NUM> and shaking for <NUM>.

The solvent was evaporated and the peptide was redissolved in DMF to which <NUM> eq. HATU and <NUM> eq. DIPEA were added and the reaction was stirred for <NUM> to perform the cyclization.

The side-chain protecting groups were then cleaved off using TFA:TIS:H<NUM>O = <NUM>:<NUM>:<NUM> by stirring for <NUM>. The peptide was precipitated using cold Et<NUM>O (-<NUM>) and centrifuging at <NUM> rpm to obtain a white solid. This solid was further purified by RP-HPLC.

The overall yields for Compounds <NUM> to <NUM> after HPLC purifications were typically in the range of <NUM>-<NUM>%. All teixobactin analogues <NUM> to <NUM> were characterized by HRMS (ESI) in positive mode (see table below). Compound <NUM> was also characterised by NMR. The homogeneity of HPLC purified fractions were analyzed by mass spectroscopy. All the teixobactin analogues used were purified to ><NUM>% purity as indicated by HPLC.

Minimum inhibitory concentrations for Compounds <NUM> to <NUM> against MRSA are shown in Table <NUM>.

The antimicrobial potency of teixobactin analogue Compounds <NUM> to <NUM> was assessed against MRSA ATCC <NUM>. The Leu<NUM>-teixobactin and natural teixobactin were included as benchmarks for activity. The six analogues <NUM> to <NUM> and <NUM> to <NUM> with two cationic charges have hydrophobic-hydrophilic balances similar to natural teixobactin (two cationic charges). These analogues showed comparable potency (MIC <NUM> - <NUM>. 25µg/ ml) to natural teixobactin (MIC <NUM>. Compounds <NUM> to <NUM> each possess three cationic charges. Interestingly, Compound <NUM> showed comparable antimicrobial activity (MIC <NUM>. 25µg/ ml) to natural teixobactin. However, Compounds <NUM> and <NUM> showed <NUM> times reduced antibacterial activity (MIC 1µg/ ml) than natural teixobactin or Leu<NUM>-teixobactin. Compound <NUM> with four cationic charges also showed reduced antibacterial activity (MIC 1µg/ ml).

Compounds <NUM> to <NUM> were further assessed against a panel of antibiotic-resistant and antibiotic susceptible Gram-positive pathogens and comparator antibiotics, daptomycin (<FIG>). The MIC results indicate that the synthetic analogues are potent against the various strains tested, but their MIC distribution differs significantly. Interestingly, a wider distribution of MIC values was observed as the overall net charge of the peptide was increased.

Notably, the MIC values for Staphylococcus were not altered whereas a significant increase in Enterococcus was observed with four cationic charges (Compound <NUM>, MIC <NUM>-8µg/ ml). Similar trends have been reported for teixobactin analogues, whereby increases in positive charges give increases in MICs against Staphylococcus aureus ATCC <NUM>. Herein, for example, Lys<NUM>-D-Lys<NUM>-Lys<NUM>-teixobactin (four cationic charges) has a reported MIC of 8µg/ ml against Staphylococcus aureus ATCC <NUM>; whereas, we observed an MIC of 1µg/ ml (<NUM> times improvement) for Arg<NUM>-D-Arg<NUM>-Arg<NUM>-Leu<NUM>-teixobactin (Compound <NUM>, four cationic charges) against the same bacterial strain.

The inclusion of <NUM> arginines in the above case likely perturbs the amphiphilic character of the teixobactin, resulting in a decrease in activity. The six analogues <NUM> to <NUM> and <NUM> to <NUM> with two cationic charges showed comparable antibacterial potency to Leu10-teixobactin. Importantly, the hydrophobic-hydrophilic balance of these analogues was similar to natural teixobactin (two cationic charges). The analogues <NUM> to <NUM> with three cationic charges also showed comparable antibacterial potency to Leu<NUM>-teixobactin. All synthesized analogues showed good potency against a broad panel of bacteria. The nine analogues <NUM> to <NUM> and <NUM> to <NUM> showed drug like profiles such as high antibacterial potency with optimal balance of hydrophobicity and hydrophilicity. The minimum bactericidal concentrations (MBC) of teixobactin analogues against S. aureus/MRSA strains (Table <NUM>) has been further determined. Compound <NUM> displayed highly potent bactericidal properties, as its MBC values did not increase above <NUM> times the MIC against the tested strains. Compound <NUM> was found inactive against Pseudomonas aeruginosa (Gram negative bacteria). In view of narrow MIC distribution values and bactericidal properties, attention was focused on Compound <NUM> and further investigated its biological properties.

D-Arg<NUM>-Leu<NUM>-teixobactin (Compound <NUM>) was evaluated for single step resistance in S. aureus ATCC <NUM> and MRSA ATCC <NUM>. Mutants of S. aureus ATCC <NUM> or MRSA ATCC <NUM> resistant to teixobactin analogue <NUM> (5x, 10x, 20x MIC) could not be obtained. The calculated frequency of resistance to Compound <NUM> was found to be <<NUM>-<NUM> which is comparable to teixobactin. A lack of resistance in preliminary studies against <NUM> is promising in the development of drug like molecules against resistant bacteria. Time-kill kinetics studies of D-Arg<NUM>-Leu<NUM>-teixobactin <NUM> against S. aureus ATCC <NUM> was investigated to ascertain if the chemical modifications retained the bactericidal properties. The exposure of bacterial inoculum to <NUM>µg/ml or <NUM>µg/ml of Compound <NUM> resulted in ≥ <NUM> log<NUM> decrease in bacterial viability at <NUM>, which is comparable with previous reports of teixobactin analogues and teixobactin.

It was important to evaluate the cytotoxicity of Compound <NUM> on mammalian cells prior to in vivo studies. The cytotoxicity of Compound <NUM> in human lung epithelial cell line A549 and primary dermal fibroblasts (hDFs) was determined. Both of these cell culture models are already established for evaluation of cytotoxicity of antimicrobial peptides. An MTS assay indicated that both mammalian cell-types exposed to various concentrations of the peptide retained significant metabolic activity (≥ <NUM>% viability, <FIG> a,b), even at a concentration that was ~<NUM> times (<NUM>µg/ml) higher than the average MIC (<NUM>µg/ml) values, indicating excellent cell selectivity of the teixobactin analogues. High content images indicated the absence of any cytoskeletal and nuclear disruption upon exposure of both epithelial and fibroblasts cells to Compound <NUM> (<FIG>), establishing its non-cytotoxic properties. The morphology of mammalian cells exposed to Compound <NUM> appeared similar to the untreated cells. However, exposure of cells to an antineoplastic agent (nocodazole, used as a control) resulted in substantial loss of adhered cells, confirming its cytotoxicity.

Both A549 cells (a) and hDFs (b) were treated with increasing concentrations of Compound <NUM> (ranging from <NUM>µg/ml to <NUM>µg/ml) for <NUM>. The stock solution of Compound <NUM> (<NUM>µg/ml) was prepared fresh by directly dissolving Compound <NUM> in cell culture medium and used. Cells were treated with dimethyl sulfoxide (DMSO, <NUM>% v/v) or nocodazole (<NUM>µg/ml dissolved in DMSO) as controls. At the end of the treatment period, metabolic activities of cells were quantified by MTS-based cell viability assay. Data represents mean ± SEM of three independent triplicate experiments, *p><NUM>. After <NUM> treatment with Compound <NUM>, A549 cells (c) and hDFs (d) were fixed, fluorescently stained with rhodamine-phalloidin (red), alexa fluor <NUM> conjugated anti-α-tubulin (green) and Hoechst <NUM> (blue) and imaged using IN Cell Analyzer <NUM> automated microscope. Representative images of cells treated with Compound <NUM> (<NUM>µg/ml for <NUM>) or nocodazole (<NUM>µg/ml, toxicity control) are shown in <FIG>.

The in vivo toxicity of Compound <NUM> in a rabbit corneal damage model was examined. A <NUM>µl of <NUM>% (w/v) solution was applied topically (<NUM> times/day) to the circularly debrided cornea and reepithelialisation was monitored by fluorescein staining. Vehicle alone served as control.

<FIG> shows the decrease in fluorescein staining with time for both control wounds and wounds treated with Compound <NUM>. There was no significant difference in wound closure between PBStreated wounds or wounds treated with Compound <NUM>. The lack of any delay in the reepithelialisation and wound closure for the injured cornea treated with Compound <NUM> suggests good biocompatibility of the peptide.

The in vivo efficacy of Compound <NUM> in the mice-eye model of S. aureus keratitis was examined. aureus is one of the major etiological agents for bacterial keratitis and the toxic secretions produced by this microorganism have been implicated in corneal melt, leading to significant morbidity and vision loss. Scarified cornea of the mice were infected with S. aureus ATCC <NUM> inoculum (<NUM>µl of <NUM>×<NUM><NUM> CFU/ml) after scratching the corneal epithelium with scalpel blade. At <NUM> post infections (p. ), the infected cornea were treated with vehicle (PBS), Compound <NUM> (<NUM>% w/v in PBS) and moxifloxacin (<NUM>%). A total of <NUM> doses were applied and the progression of the infection was monitored by slit lamp examination, anterior segment optical coherent tomography (AS-OCT) and microbiological enumeration of the bacterial bioburden. Mice cornea treated with PBS had severe clinical presentation indicated by chemosis, significant presence of hypopyon like materials and corneal infiltrates (<FIG>).

Note the significant presence of corneal haze and mucopurulent discharge in PBS treated cornea whereas Compound <NUM> or moxifloxacin treated cornea remained clear and no signs of corneal defects. Notably, infected cornea treated with Compound <NUM> or a fluoroquinalone antibiotic, had similar clinical appearance presentation, as indicated by lack of any conjunctival chemosis and corneal infiltrates. These results indicate that Compound <NUM> halted the progression of S. aureus infections and the activity was comparable to moxifloxacin.

To determine the effect of treatments on tissue severity, the corneal thickness from various groups was determined (<FIG>). The baseline corneal thickness of mice (<NUM>±<NUM>) decreased moderately (<NUM>±<NUM>) after de-epithelialization followed by S. aureus infection (<NUM> p. Treatment of the infected cornea with vehicle alone (PBS) resulted in substantial increase in corneal thickness after <NUM> (<NUM>±<NUM>) and <NUM> (<NUM>±<NUM>), indicating corneal edema after infection. Infected cornea treated with Compound <NUM> had a mean corneal thickness of <NUM>±<NUM> and <NUM>±<NUM> after <NUM> and <NUM> post treatment (p. ), respectively. For the moxifloxacin-treated cornea the mean corneal thickness was <NUM>±<NUM> after <NUM> p. and <NUM>±<NUM> after <NUM> p. These results suggested that Compound <NUM> treatment resulted in significant decrease in corneal edema after S. aureus infections when compared PBS treated or moxifloxacin-treated groups.

<FIG>: Note that the CT values for Compound <NUM> treated cornea approached the baseline values after <NUM> p. , which was absent in the case of PBS-/Moxifloxacin-treated corneas. Note that a significant decrease in corneal edema was observed for infected cornea treated with Compound <NUM> compared to untreated cornea (p, <NUM> two-way ANOVA) as early after <NUM> doses which decreased further after <NUM> doses (p, <NUM>). The results indicated a marked decrease in the severity (due to infections) after treatment with Compound <NUM> when compared to standard antibiotic treatment.

Bacterial enumeration of the corneal tissues harvested after <NUM> dosages confirmed the in vivo efficacy of Compound <NUM> (<FIG>). All the infected cornea that received PBS treatment contained significant presence of bacteria, varying from <NUM>×<NUM><NUM> - <NUM>×<NUM><NUM> CFU/tissue. The mean log<NUM> CFU/tissue ± standard error of the mean for PBS treated cornea was <NUM>±<NUM>. Five out of six cornea treated with Compound <NUM> had detectable bacterial colonies. The mean log<NUM> CFU/tissue for Compound <NUM> treated cornea was <NUM>±<NUM>. Four infected corneas treated with moxifloxacin contained detectable bacterial colonies with a mean log<NUM> CFU/tissue of <NUM>±<NUM> was observed. These results confirmed that Compound <NUM> had a similar antibacterial effect as an established antibiotic in decreasing the bacterial bioburden, thus demonstrating its potential as a safe therapeutic for topical applications.

Compound <NUM> (Leu<NUM>-Teixobactin-<NUM>-(S3K-K5R) conjugate, above) was prepared by a method analogous to the method for preparing Compound <NUM> (see Example <NUM>). Calculated mass: <NUM>; Found mass: <NUM>.

Minimum inhibitory concentrations for Compound <NUM> against MRSA, E. coli and A. baumannii are shown in Table <NUM>.

Claim 1:
A compound of formula IA,
<CHM>
or a pharmaceutically-acceptable salt, solvate or clathrate thereof, wherein:
R<NUM> represents H, C<NUM>-<NUM> alkyl, or benzyl;
AA<NUM> represents a hydrophobic proteinogenic or hydrophobic non-proteinogenic amino acid, AA<NUM> represents an L-isoleucine residue, AA<NUM> represents a D-isoleucine or D-allo-isoleucine residue, AA<NUM> represents an L-isoleucine residue, and AA<NUM> represents an L-serine residue;
AA<NUM> and AA<NUM> each independently represents a proteinogenic or non-proteinogenic amino acid, such as diaminopropanoic acid, diaminobutanoic acid, or ornithine;
R<NUM> represents hydrogen or C<NUM>-<NUM> alkyl;
R9a represents a proteinogenic or non-proteinogenic amino acid side chain (such as -CH<NUM>-NH<NUM>, -(CH<NUM>)<NUM>-NH<NUM> or -(CH<NUM>)<NUM>-NH<NUM>);
R10a represents a hydrophobic proteinogenic amino acid side chain, a hydrophobic non-proteinogenic amino acid side chain, hydrogen, or R10a is linked to the adjacent nitrogen atom to form a proline ring;
R11a represents a proteinogenic or non-proteinogenic amino acid side chain;
Z is -O- or -NH-;
optionally wherein the compound of formula IA is covalently bonded to a delivery agent, which is either capable of covalently bonding to one or more structures on a bacterial cell membrane or comprises a hydrophilic portion capable of otherwise binding to one or more structures on a bacterial cell membrane,
provided that the compound of formula IA or pharmaceutically-acceptable salt, solvate or clathrate thereof is not selected from the group consisting of:
<CHM>
<CHM>
and
<CHM>