BACKGROUND OF THE INVENTION

This disclosure relates to Toll-like receptor 7 (“TLR7”) agonists and conjugates thereof, and methods for the preparation and use of such agonists and their conjugates.

Toll-like receptors (“TLRs”) are cell-surface receptors that recognize pathogen-associated molecular patterns (“PAMPs”). Activation of a TLR by the binding of its cognate PAMP signals potential infection by a pathogen and stimulates the immune system to fight the infection. Humans have 11 TLRs, named TLR1 through TLR11.

The activation of a TLR—with TLR7 being the most studied—by an agonist can have an adjuvant effect on the action of vaccines and immunotherapy agents in treating a variety of conditions other than actual pathogen infection, by stimulating the immune response.

TLR7 recognizes PAMPs associated with single-stranded RNA viruses. Its activation induces secretion of Type I interferons such as IFNα and IFNβ (Lund et al. 2004). It has two binding sites, one for single stranded RNA ligands such as ssRNA40 (Berghöfer et al. 2007) and one for guanosine (Zhang et al. 2016).

TLR7 can bind to, and be activated by, guanosine-like synthetic agonists such as imiquimod, resiquimod, and gardiquimod, which are based on a 1H-imidazo[4,5-c]quinoline scaffold.



Synthetic TLR7 agonists based on a pteridinone molecular scaffold are also known, as exemplified by vesatolimod (Desai et al. 2015), which has been in Phase 2 clinical trials.



Other synthetic TLR7 agonists are based on a purine-like scaffold, frequently according to formula (A):


where R, R′, and R″ are structural variables, with R″ typically containing an unsubstituted or substituted aromatic or heteroaromatic ring.

Disclosures of bioactive molecules having a purine-like scaffold and their uses in treating conditions such as fibrosis, inflammatory disorders, cancer, or pathogenic infections include: Akinbobuyi et al. 2015 and 2016; Barberis et al. 2012; Carson et al. 2014; Ding et al. 2016, 2017a, and 2017b; Graupe et al. 2015; Hashimoto et al. 2009; He et al. 2019a and 2019b; Holldack et al. 2012; Isobe et al. 2009a and 2012; Poudel et al. 2019a and 2019b; Pryde 2010; and Young et al. 2019.

The group R″ can be pyridyl: Bonfanti et al. 2015a and 2015b; Halcomb et al. 2015; Hirota et al. 2000; Isobe et al. 2002, 2004, 2006, 2009a, 2009b, 2011, and 2012; Kasibhatla et al. 2007; Koga-Yamakawa et al. 2013; Musmuca et al. 2009; Nakamura 2012; Ogita et al. 2007; and Yu et al. 2013.

There are disclosures in which the 6,5-fused ring system of formula (A)—a pyrimidine six member ring fused to an imidazole five member ring—is modified. (a) Dellaria et al. 2007, Jones et al. 2010 and 2012, and Pilatte et al. 2017 disclose compounds in which the pyrimidine ring is replaced by a pyridine ring. (b) Coe et al. 2017 and Zhang et al. 2018 disclose compounds in which the imidazole ring is replaced by a pyrazole ring. (c) Cortez et al. 2017 and 2018; Li et al. 2018, and McGowan et al. 2016a, 2016b, and 2017 disclose compounds in which the imidazole ring is replaced by a pyrrole ring.

Bonfanti et al. 2015b and 2016 disclose TLR7 modulators in which the two rings of a purine moiety are spanned by a macrocycle:



A TLR7 agonist can be conjugated to a partner molecule, which can be, for example, a phospholipid, a poly(ethylene glycol) (“PEG”), or another TLR (commonly TLR2). Exemplary disclosures include: Carson et al. 2013, 2015, and 2016, Chan et al. 2009 and 2011, Lioux et al. 2016, Maj et al. 2015, Vernejoul et al. 2014, and Zurawski et al. 2012. Conjugation to an antibody has also been disclosed: Gadd et al. 2015. A frequent conjugation site is at the R″ group of formula (A).

Jensen et al. 2015 discloses the use of cationic lipid vehicles for the delivery of TLR7 agonists.

Some TLR7 agonists, including resiquimod are dual TLR7/TLR8 agonists. See, for example, Beesu et al. 2017, Embrechts et al. 2018, Lioux et al. 2016, and Vernejoul et al. 2014.

Full citations for the documents cited herein by first author or inventor and year are listed at the end of this specification.

BRIEF SUMMARY OF THE INVENTION

In one aspect, this specification provides a compound having a structure represented by formula (I)


whereinA is O, NH, N(C1-C3alkyl), or S;B is a C1-C10unsaturated or saturated alkyl, (C2-C6alkyl)NHC(═O)(C1-C6alkyl), (C2-C6alkyl)NHC(═O)(C1-C6alkyl)O, (C2-C10unsaturated or saturated alkyl)O, (C2-C6alkyl)O(C2-C6alkyl), (C2-C6alkyl)O(C2-C6alkyl)O; each optionally substituted with C1-C3alkyl or (C1-C3alkyl)O;Ar is a 6-membered aromatic, a 5- to 6-membered heteroaromatic, a 4- to 7-membered cycloaliphatic, or a 4- to 7-membered heterocycloaliphatic moiety;Y is a bond, O, S, NH, N(C1-C3alkyl), (CH2)1-2, C(═O)NH, or C(═O)N(C1-C3alkyl);R1is a 6-membered aromatic, a 5- to 6-membered heteroaromatic, a 4- to 7-membered cycloaliphatic, or a 4- to 7-membered heterocycloaliphatic moiety, or R1can be absent if Y is other than a bond;R2is H, C1-C3alkyl, halo, O(C1-C3alkyl), CN, NO2, (CH2)1-4R3,

with the proviso that R2is other than halo, O(C1-C3alkyl), CN, or NO2when R1is absent;R3is halo, OH, CN, NH2, NH(C1-C5alkyl), NH(CH2) N(C1-C5alkyl)2, NH(C3-C6cycloaliphatic), NH(C4-C8bicycloaliphatic), NH(C6-C10spirocycloaliphatic), N(C3-C6cycloaliphatic)2, NH(CH2)1-3(aryl), N((CH2)1-3(aryl))2, NH(CH2)1-3CO2(C1-C3alkyl), N((CH2)1-3CO2(C1-C3alkyl))2, or a cyclic amine moiety having the structure

R4is H, C1-C3alkyl, or C(═O)(C1-C3alkyl); andn is 1, 2, or 3;whereinan alkyl, cycloaliphatic, bicycloaliphatic, spirocycloaliphatic, cyclic amine, 6-membered aromatic or heteroaromatic, or 5-membered heteroaromatic moiety is optionally substituted with one or more substituents selected from OH, halo, CN, (C1-C3alkyl), O(C1-C3alkyl), C(═O)(C1-C3alkyl), SO2(C1-C3alkyl), CO2(C1-C3alkyl), NH2, NH(C1-C3alkyl), and N(C1-C3alkyl)2;a cycloaliphatic, bicycloaliphatic, spirocycloaliphatic, or cyclic amine moiety may have a CH2group replaced by O, S, NH, C(═O), N(C1-C3alkyl), NC(═O)(C1-C3alkyl), or N(Boc); anda cycloaliphatic, heterocycloaliphatic, aromatic, or heteroaromatic moiety may be fused to another cycloaliphatic, heterocycloaliphatic, aromatic, or heteroaromatic moiety.

Compounds according to formula (I) have activity as TLR7 agonists and some of them can be conjugated to a targeting agent such as an antibody, for targeted delivery to a target tissue or organ of intended action. They can also be PEGylated, to modulate their pharmaceutical properties.

