R7 (drug)

R7 is a small-molecule flavonoid and orally active, potent, and selective agonist of the tropomyosin receptor kinase B (TrkB) – the main signaling receptor for the neurotrophin brain-derived neurotrophic factor (BDNF) – which is under development for the treatment of Alzheimer's disease.[1][3][2] It is a structural modification and prodrug of tropoflavin (7,8-DHF) with improved potency and pharmacokinetics, namely oral bioavailability and duration.[2] R7 was synthesized by the same researchers who were involved in the discovery of tropoflavin.[2][4] A patent was filed for R7 in 2013 and was published in 2015.[2] In 2016, it was reported to be in the preclinical stage of development.[1][3] R7 was superseded by R13 because while R7 had a good drug profile in animals, it showed almost no conversion into tropoflavin in human liver microsomes.[5]

R7

Clinical data
Other names	4-Oxo-2-phenyl-4H-chromene-7,8-diyl bis(dimethylcarbamate)
Routes of administration	By mouth[1]
Legal status
Legal status	US: Investigational New Drug
Pharmacokinetic data
Bioavailability	~35% (in mice)[2]
Metabolites	Tropoflavin[1]
Elimination half-life	~3.25 hours (in mice[2]
Identifiers
IUPAC name [8-(Dimethylcarbamoyloxy)-4-oxo-2-phenylchromen-7-yl] N,N-dimethylcarbamate
CAS Number	1609067-35-7 Y
PubChem CID	73672564
UNII	2KYC4WG53K
Chemical and physical data
Formula	C21H20N2O6
Molar mass	396.399 g·mol−1
3D model (JSmol)	Interactive image
SMILES CN(C)C(=O)OC1=C(C2=C(C=C1)C(=O)C=C(O2)C3=CC=CC=C3)OC(=O)N(C)C
InChI InChI=1S/C21H20N2O6/c1-22(2)20(25)28-16-11-10-14-15(24)12-17(13-8-6-5-7-9-13)27-18(14)19(16)29-21(26)23(3)4/h5-12H,1-4H3 Key:KHUMQRAGNPGBIE-UHFFFAOYSA-N

In 2010, tropoflavin, a naturally occurring flavonoid, was found to act as an agonist of the TrkB with nanomolar affinity (K_d ≈ 320 nM).[4] Subsequently, tropoflavin demonstrated robust efficacy in animal models of Alzheimer's disease and a variety of other conditions, making it a highly promising potential therapeutic agent.[1] Due to the presence of a vulnerable catechol group on its 2-phenyl-4H-chromene ring, tropoflavin is extensively conjugated via glucuronidation, sulfation, and methylation during first-pass metabolism in the liver and has a poor oral bioavailability of only 5% in mice upon oral administration.[2] As such, tropoflavin itself is a poor candidate for clinical development as an oral medication.[2] R7 is a derivative of tropoflavin with carbamate moieties on its hydroxyl groups, thereby protecting it from metabolism.[2]

As R7 is a slightly larger molecule than tropoflavin, 72.5 mg R7 is molecularly equivalent to 50 mg tropoflavin.[2] Relative to a roughly molecularly equivalent dose of tropoflavin, the area-under-curve levels of R7 were found to be 7.2-fold higher upon oral administration to mice, and R7 hence has a greatly improved oral bioavailability in mice of approximately 35%.[2] Moreover, whereas tropoflavin itself is mostly metabolized in mice within 30 minutes, tropoflavin as a metabolite was still detectable in plasma at 8 hours after administration with R7, indicating that R7 sustainably releases tropoflavin into circulation.[2] In accordance, the terminal half-life of R7 is about 195 minutes (3.25 hours) in mice.[2] The T_max of R7 is about 60 minutes in mice, and its C_max for a 78 mg/kg dose was 262 ng/mL, whereas that for a 50 mg/kg dose of tropoflavin was 70 ng/mL.[2]

Like tropoflavin, administration of R7 has been found to activate the TrkB in vivo in the mouse brain.[2] Moreover, R7 was found to potently activate the TrkB and the downstream Akt signaling pathway upon oral administration, an action that was tightly correlated with plasma concentrations of tropoflavin.[2] As such, R7 has shown in vivo efficacy as an agonist of the TrkB, including central activity, similarly to tropoflavin.[2]