Macrolides with modified desosamine sugars and uses thereof

#Emerging resistance to existing antibiotics is rapidly developing as a crisis of global proportions, especially for Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus pneumonia infections. Pathogenic bacteria can transmit genes coding for antibiotic resistance both vertically (to their progeny) and horizontally (to neighboring bacteria of different lineages), and as a result antibiotic resistance can evolve quickly, particularly in nosocomial (hospital) settings. See, e.g., Wright, Chem. Commun. (2011) 47:4055-4061. This year, >99,000 people will die in the U.S. from healthcare-associated infections, more than all casualties from car accidents, HIV, and breast cancer combined, creating an estimated burden of up to $45 billion in U.S. healthcare costs. See, e.g., Klevens et al., Public Health Rep (2007) 122:160-166. The current crisis is exacerbated by the fact that most major pharmaceutical companies have essentially abandoned research in the development of new antibiotics. See, e.g., Projan, Curr. Opin. Microbiol. (2003) 6:427-430. The current rate of introduction of new antibiotics does not adequately address growing resistance, and with the case of international travel and increasing population densities, the need for innovation in the field has never been higher.

#The macrolides are one of the few major clinically important classes of antibiotics for which the only practical access has been through semi-synthesis, or chemical manipulation of structurally complex fermentation products, in routes as long as 16 steps. See, e.g., Paterson, Tetrahedron (1985) 41:3569-3624; Omura, Ed., Macrolide Antibiotics: Chemistry, Biology, and Practice, Second Edition; Academic Press, 2002. The macrolide class of antibiotics has proven safe and effective in the battle against pathogenic bacteria since the discovery of erythromycin over 60 years ago. See, e.g., Wu et al., Curr. Med. Chem. (2001) 8:1727-1758. Erythromycin displays a spectrum of antibacterial activity against Gram-positive bacteria similar to that of penicillin but has a lesser propensity to induce allergic interactions, and has been routinely prescribed for upper and lower respiratory tract infections and urogenital infections. See, e.g., Washington et al., Mayo. Clin. Proc. (1985) 60:189-203; Washington et al., Mayo. Clin. Proc. (1985) 60:271-278. However, erythromycin is known to undergo acid-promoted internal ketalization (cyclization of the C6 and C12 hydroxyl groups onto the C9 ketone) in the gut, which leads to adverse gastrointestinal events. See, e.g., Kurath et al., Experientia (1971) 27:362. Second-generation macrolide antibiotics clarithromycin and azithromycin addressed issues of acid instability and were prepared semi-synthetically in 4-6 steps from erythromycin, which is readily available through large-scale fermentation. See, e.g., Ma et al., Curr. Med. Chem. (2011) 18:1993-2015; Wu et al., Curr. Pharm. Des. (2000) 6:181-223; Ma et al., Mini-Rev. Med. Chem. (2010) 10:272-286; Asaka et al., Curr. Top. Med. Chem. (Sharjah, United Arab Emirates) (2003) 3:961-989; Morimoto et al., J. Antibiot. (1990) 43:286-294; Morimoto et al., J. Antibiot. (1984) 37:187-189; Watanabe et al., J. Antibiot. (1993) 46: 1163-1167; Watanabe et al., J. Antibiot. (1993) 46:647-660; Bright et al., J. Antibiot. (1988) 41: 1029-1047; Djokic et al., J. Antibiot. (1987) 40:1006-1015; Mutak et al., J. Antibiot. (2007) 60: 85-122; and Retsema et al., Antimicrob. Agents Chemother. (1987) 31:1939-1947. Azithromycin has been shown to exhibit markedly improved efficacy against Gram-negative organisms, and has a longer half-life and higher tissue distribution than the other macrolide antibiotics, thought to correlate with its 15-membered ring containing a tertiary amine. See, e.g., Ferwerda et al., J. Antimicrob. Chemother. (2001) 47:441-446; Girard et al., Antimicrob. Agents Chemother. (1987) 31:1948-1954. The natural product tylosin, a 16-membered macrolide used in veterinary medicine, has been shown by X-ray crystallography to occupy the same binding pocket as erythromycin and azithromycin, suggesting that there is a high tolerance for variability in ring size and composition of the macrocycle.

#The three primary causes of resistance to macrolides in bacterial organisms are ribosome methylation encoded by erm genes, mutations in ribosomal RNA or peptides, and cell efflux mediated by mef and msr genes. See, e.g., Leclercq et al., Antimicrob. Agents Chemother. (1991) 35:1273-1276; Leclercq et al., Antimicrob. Agents Chemother. (1991) 35:1267-1272; Weisblum, Antimicrob. Agents Chemother. (1995) 39:577-585; Vester et al., Antimicrob. Agents Chemother. (2001) 45:1-12; Prunier et al., Antimicrob. Agents Chemother. (2002) 46:3054-3056; Li et al., J. Antimicrob. Chemother. (2011) 66:1983-1986; Sutcliffe et al., Antimicrob. Agents Chemother. (1996) 40:1817-1824; Wondrack et al., Antimicrob. Agents Chemother. (1996) 40: 992-998. Ketolides such as telithromycin and solithromycin defeat the efflux mechanism of resistance by replacement of the C3 cladinose sugar with a carbonyl group (hence the name “ketolides”), and are thought to exhibit greatly increased binding by virtue of favorable interactions between the novel aryl-alkyl sidechain and the ribosome. See, e.g., Ma et al., Curr. Med. Chem. (2011) 18:1993-2015; Ma et al., Mini-Rev. Med. Chem. (2010) 10:272-286. Despite greatly improved ribosomal binding, ketolides such as telithromycin and solithromycin have not addressed several of the newest forms of macrolide resistance that have evolved in nosocomial settings, especially ribosome methylation and RNA point mutations.

#The accompanying drawings, which constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

#FIG. 1 depicts exemplary 14-, 15-, and 16-membered macrolide antibiotics.

#FIG. 2 depicts the crystal structure of solithromycin bound to a ribosome of E. coli. Residues in a 12-Å sphere generated using MacPyMol from PDB #3ORB. See, e.g., Llano-Sotelo Antimicrob. Agents Chemother. (2010) 54:4961-4970.

#The macrolides specifically described herein include 14-membered ketolides, 14-membered azaketolides, 15-membered azaketolides, and 16-membered azaketolides. Ketolides are typically connected between C8 and C10 with a ketone. Azaketolides feature an amine, or aminoalkylene fragment in place of the keto group.

#In certain embodiments, the invention provides macrolides with modified sugars at the C5 position of the macrolide (e.g., desosamine or mycaminose analogs), wherein the sugar is modified at the C6 position of the sugar. In certain embodiments, the invention provides compounds of Formula (I):

#or pharmaceutically acceptable salt thereof, wherein: Z is —C(═O)— or —NRZ2—; X is —NRB— or —O—, provided that X is —NRB— when Z is —C(═O)—; RZ2 is hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, acyl, or a nitrogen protecting group; p is 0, 1, or 2, provided that p is 0 when Z is —C(═O)—; RA is hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —C(═O)-LS2-RS, —C(═NRSN2)-LS2-RS, —S(═O)-LS2-RS, —S(═O)2-LS2-RS, a nitrogen protecting group when attached to a nitrogen atom, or an oxygen protectin group when attached to an oxygen atom, and RSN2 is independently hydrogen, optionally substituted C1-C6 alkyl, or a nitrogen protecting group; RB is hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, or a nitrogen protecting group; or RA and RB are taken together to form ═N2 or an optionally substituted heterocyclyl or heteroaryl ring; LS2 is a bond, —NRS—, —O—, or —S—, or a linking group selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted alkynylene, optionally substituted heteroalkylene, optionally substituted heteroalkenylene, and optionally substituted heteroalkynylene, and combinations thereof; each RS is independently hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, an oxygen protecting group when attached to an oxygen atom, a nitrogen protecting group when attached to a nitrogen atom, or a sulfur protecting group when attached to a sulfur atom, or two RS groups attached to the same nitrogen atom are joined to form an optionally substituted heterocyclyl or heteroaryl ring; each of RS4a and RS4b is independently hydrogen, halogen, optionally substituted C1-C6 alkyl, or —ORSO4; each of RS6a and RS6b is independently hydrogen, halogen, or optionally substituted C1-C6 alkyl; each RSN is independently hydrogen, optionally substituted C1-C6 alkyl, or a nitrogen protecting group, or two RSN groups attached to the same nitrogen atom are joined to form an optionally substituted heterocyclyl or heteroaryl ring; each of RSO and RSO4 is independently hydrogen, optionally substituted C1-C6 alkyl, a carbohydrate, or an oxygen protecting group; each of R1a and R1b is independently hydrogen, halogen, acyl, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl; each of R2a and R2b is independently hydrogen, halogen, optionally substituted alkyl, or optionally substituted alkenyl; each of R3 and R4 is independently hydrogen, halogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, or —OR3a; each R3a is independently hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, an oxygen protecting group, or of formula: