BICTEGRAVIR, NEW PATENT, WO 2018005328, CONCERT PHARMA
CONCERT PHARMACEUTICALS, INC.
TUNG, Roger, D.; (US)
Concert CEO Roger Tung
Novel deuterated forms of bictegravir is claimed. Gilead Sciences is developing the integrase inhibitor bictegravir as an oral tablet for the treatment of HIV-1 infection.
This invention relates to deuterated forms of bictegravir, and pharmaceutically acceptable salts thereof. In one aspect, the invention provides a compound of Formula (I) or a pharmaceutically acceptable salt thereof, wherein each of Y1, Y2, Y3, Y4a, Y4b, Y5a, Y5b, Y6, Y7a, Y7b, Y8, Y9, Y10a, Y10b, Y11a, and Y11b is independently hydrogen or deuterium; provided that if each Y1, Y2, Y3, Y4a, Y4b, Y5a, Y5b, Y6, Y7a, Y7b, Y8, Y9, Y10a, Y10b, and Y11 is hydrogen, then Y11b is deuterium.
Many current medicines suffer from poor absorption, distribution, metabolism and/or excretion (ADME) properties that prevent their wider use or limit their use in certain indications. Poor ADME properties are also a major reason for the failure of drug candidates in clinical trials. While formulation technologies and prodrug strategies can be employed in some cases to improve certain ADME properties, these approaches often fail to address the underlying ADME problems that exist for many drugs and drug candidates. One such problem is rapid metabolism that causes a number of drugs, which otherwise would be highly effective in treating a disease, to be cleared too rapidly from the body. A possible solution to rapid drug clearance is frequent or high dosing to attain a sufficiently high plasma level of drug. This, however, introduces a number of potential treatment problems such as poor patient compliance with the dosing regimen, side effects that become more acute with higher doses, and increased cost of treatment. A rapidly metabolized drug may also expose patients to undesirable toxic or reactive metabolites.
 Another ADME limitation that affects many medicines is the formation of toxic or biologically reactive metabolites. As a result, some patients receiving the drug may experience toxicities, or the safe dosing of such drugs may be limited such that patients receive a suboptimal amount of the active agent. In certain cases, modifying dosing intervals or formulation approaches can help to reduce clinical adverse effects, but often the formation of such undesirable metabolites is intrinsic to the metabolism of the compound.
 In some select cases, a metabolic inhibitor will be co-administered with a drug that is cleared too rapidly. Such is the case with the protease inhibitor class of drugs that are used to treat HIV infection. The FDA recommends that these drugs be co-dosed with ritonavir, an inhibitor of cytochrome P450 enzyme 3A4 (CYP3A4), the enzyme typically responsible for their metabolism (see Kempf, D.J. et al., Antimicrobial agents and chemotherapy, 1997, 41(3): 654-60). Ritonavir, however, causes adverse effects and adds to the pill burden for HIV patients who must already take a combination of different drugs. Similarly, the
CYP2D6 inhibitor quinidine has been added to dextromethorphan for the purpose of reducing rapid CYP2D6 metabolism of dextromethorphan in a treatment of pseudobulbar affect. Quinidine, however, has unwanted side effects that greatly limit its use in potential combination therapy (see Wang, L et al., Clinical Pharmacology and Therapeutics, 1994, 56(6 Pt 1): 659-67; and FDA label for quinidine at http://www.accessdata.fda.gov).
 In general, combining drugs with cytochrome P450 inhibitors is not a satisfactory strategy for decreasing drug clearance. The inhibition of a CYP enzyme’s activity can affect the metabolism and clearance of other drugs metabolized by that same enzyme. CYP inhibition can cause other drugs to accumulate in the body to toxic levels.
 A potentially attractive strategy for improving a drug’s metabolic properties is deuterium modification. In this approach, one attempts to slow the CYP-mediated metabolism of a drug or to reduce the formation of undesirable metabolites by replacing one or more hydrogen atoms with deuterium atoms. Deuterium is a safe, stable, non-radioactive isotope of hydrogen. Compared to hydrogen, deuterium forms stronger bonds with carbon. In select cases, the increased bond strength imparted by deuterium can positively impact the ADME properties of a drug, creating the potential for improved drug efficacy, safety, and/or tolerability. At the same time, because the size and shape of deuterium are essentially identical to those of hydrogen, replacement of hydrogen by deuterium would not be expected to affect the biochemical potency and selectivity of the drug as compared to the original chemical entity that contains only hydrogen.
 Over the past 35 years, the effects of deuterium substitution on the rate of metabolism have been reported for a very small percentage of approved drugs (see, e.g., Blake, MI et al, J Pharm Sci, 1975, 64:367-91; Foster, AB, Adv Drug Res 1985, 14:1-40 (“Foster”); Kushner, DJ et al, Can J Physiol Pharmacol 1999, 79-88; Fisher, MB et al, Curr Opin Drug Discov Devel, 2006, 9:101-09 (“Fisher”)). The results have been variable and unpredictable. For some compounds deuteration caused decreased metabolic clearance in vivo. For others, there was no change in metabolism. Still others demonstrated increased metabolic clearance. The variability in deuterium effects has also led experts to question or dismiss deuterium modification as a viable drug design strategy for inhibiting adverse metabolism (see Foster at p.35 and Fisher at p.101).
 The effects of deuterium modification on a drug’s metabolic properties are not predictable even when deuterium atoms are incorporated at known sites of metabolism. Only by actually preparing and testing a deuterated drug can one determine if and how the rate of metabolism will differ from that of its non-deuterated counterpart. See, for example, Fukuto et al. (J. Med. Chem.1991, 34, 2871-76). Many drugs have multiple sites where metabolism is possible. The site(s) where deuterium substitution is required and the extent of deuteration necessary to see an effect on metabolism, if any, will be different for each drug.
 Deuterium-modified analogs of bictegravir can be synthesized by means known in the art of organic chemistry. For instance, using methods described in US Patent No.9,216,996 (Haolun J. et al., assigned to Gilead Sciences, Inc. and incorporated herein by reference), using deuterium-containing reagents provides the desired deuterated analogs.
 Such methods can be carried out utilizing corresponding deuterated and optionally, other isotope-containing reagents and/or intermediates to synthesize the compounds delineated herein, or invoking standard synthetic protocols known in the art for introducing isotopic atoms to a chemical structure.
 A convenient method for synthesizing compounds of Formula I is depicted in the Schemes below.
 A generic scheme for the synthesis of compounds of Formula I is shown in Scheme 1 above. In a manner analogous to the procedure described in Wang, H. et al. Org. Lett.2015, 17, 564-567, aldol condensation of compound 1 with appropriately deuterated compound 2 affords enamine 3. Enamine 3 is then reacted with primary amine 4 to afford enamine 5, which then undergoes cyclization with dimethyl oxalate followed by ester hydrolysis to provide carboxylic acid 7.
 In a manner analogous to the procedure described in US 9,216,996, acetal deprotection of carboxylic acid 7 followed by cyclization with appropriately deuterated aminocyclopentanol 9 provides carboxylic acid intermediate 10. Amide coupling with appropriately deuterated benzylamine 11 followed by deprotection of the methyl ether ultimately affords a compound of Formula I in eight overall steps from compound 1.
 Use of appropriately deuterated reagents allows deuterium incorporation at the Y1, Y2, Y3, Y4a, Y4b, Y5a, Y5b, Y6, Y7a, Y7b, Y8, Y9, Y10a, Y10b, Y11a, and Y11bpositions of a compound of Formula I or any appropriate intermediate herein, e.g., about 90%, about 95%, about 97%, about 98%, or about 99% deuterium incorporation at any Y1, Y2, Y3, Y4a, Y4b, Y5a, Y5b, Y6, Y7a, Y7b, Y8, Y9, Y10a, Y10b, Y11a, and/or Y11b.
 Appropriately deuterated intermediates 2a and 2b, for use in the preparation of compounds of Formula I according to Scheme 1, may be prepared from corresponding deuterated reagents as exemplified in Scheme 2 below.
S h 2 S th i f C d 2 d 2b
 Synthesis of compound 2a (wherein Y3=H) by acetal formation of N,N-dimethylformamide (DMF) with dimethylsulfate has been described in Mesnard, D. et. al. J. Organomet. Chem.1989, 373, 1-10. Replacing DMF with N,N-dimethylformamide-d1 (98-99 atom % D; commercially available from Cambridge Isotope Laboratories) in this reaction would thereby provide compound 2b (wherein Y3=D).
 Use of appropriately deuterated reagents allows deuterium incorporation at the Y3 position of a compound of Formula I or any appropriate intermediate herein, e.g., about 90%, about 95%, about 97%, about 98%, or about 99% deuterium incorporation at Y3.
 Appropriately deuterated intermediates 4a-4d, for use in the preparation of compounds of Formula I according to Scheme 1, may be prepared from corresponding deuterated reagents as exemplified in Scheme 3 below.
 As described in Malik, M. S. et. al. Org. Prep. Proc. Int.1991, 26, 764-766, acetaldehyde is converted to alkylhalide 14a via reaction with chlorine gas and subsequent acetal protection with CaCl2 in methanol. As described in CN 103739506, reaction of 14a with aqueous ammonia and then sodium hydroxide provides primary amine 4a (wherein Y9=Y10a=Y10b=H). Replacing acetaldehyde with acetaldehyde-d1, acetaldehyde-2,2,2-d3, or acetaldehyde-d4 (all commercially available from CDN Isotopes with 98-99 atom % D) in the sequence then provides access to compounds 4b (Y9=D, Y10a=Y10b=H), 4c (Y9=H,
Y10a=Y10b=D) and 4d (Y9=Y10a=Y10b=D) respectively (Schemes 3b-d).
 Use of appropriately deuterated reagents allows deuterium incorporation at the Y9, Y10a, and Y10b positions of a compound of Formula I or any appropriate intermediate herein, e.g., about 90%, about 95%, about 97%, about 98%, or about 99% deuterium incorporation at any Y9, Y10a, and/or Y10b.
 Appropriately deuterated intermediates 9a-9d, for use in the preparation of compounds of Formula I according to Scheme 1, may be prepared from corresponding deuterated reagents as exemplified in Scheme 4 below.
 Following the procedures described by Gurjar, M. et. al. Heterocycles, 2009, 77, 909-925, meso-diacetate 16a is prepared in 2 steps from cyclopentadiene. Desymmetrization of 16a is then achieved enzymatically by treatment with Lipase as described in Specklin, S. et. al. Tet. Lett.201455, 6987-6991, providing 17a which is subsequently converted to aminocyclopentanol 9a (wherein Y4a=Y4b=Y5a=Y5b=Y6=Y7a=Y7b=Y8=H) via a 3 step sequence as reported in WO 2015195656.
 As depicted in Scheme 4b, aminocyclopentanol 9b (Y4a=Y4b=Y5a=Y5b=Y6=Y7a=Y7b= Y8=D) is obtained through an analogous synthetic sequence using cyclopentadiene-d6 and performing the penultimate hydrogenation with D2 in place of H2. Cyclopentadiene-d6 is prepared according to the procedure described in Cangoenuel, A. et. al. Inorg. Chem.2013, 52, 11859-11866.
 Alternatively, as shown in Scheme 4c, the meso-diol obtained in Scheme 4a is oxidized to the diketone following the procedure reported by Rasmusson, G.H. et. al. Org. Syn.1962, 42, 36-38. Subsequent mono-reduction with sodium borodeuteride and CeCl3 then affords the D1-alcohol in analogy to the method described in WO 2001044254 for the all-protio analog using sodium borohydride. Reduction of the remaining ketone using similar conditions provides the meso-D2-diol in analogy to the method reported in Specklin, S. et. al. Tet. Lett.2014, 55, 6987-6991 for the all protio analog using sodium borohydride. The meso-D2-diol is then converted to 9c (Y4a=Y4b=Y5a=Y5b=Y7a=Y7b=H, Y6=Y8=D) following the same procedures outlined in Scheme 4a.
 Likewise, the meso-diol obtained in Scheme 4b may be converted to 9d
(Y4a=Y4b=Y5a=Y5b=Y7a=Y7b=D, Y6=Y8=H) in an analogous manner as depicted in Scheme 4d. The use of deuterated solvents such as D2O or MeOD may be considered to reduce the risk of D to H exchange for ketone containing intermediates.
 Use of appropriately deuterated reagents allows deuterium incorporation at the Y4a, Y4b, Y5a, Y5b, Y6, Y7a, Y7b, and Y8 positions of a compound of Formula I or any appropriate intermediate herein, e.g., about 90%, about 95%, about 97%, about 98%, or about 99% deuterium incorporation at any Y4a, Y4b, Y5a, Y5b, Y6, Y7a, Y7b, and/or Y8.
 Appropriately deuterated intermediates 11a-11d, for use in the preparation of compounds of Formula I according to Scheme 1, may be prepared from corresponding deuterated reagents exemplified in Scheme 5 below.
Scheme 5. Synthesis of Benzylamines 11a-11d