Introduction
5fur-144 is a synthetic small molecule that has attracted attention within the fields of medicinal chemistry and neuropharmacology due to its high affinity for the 5-HT1A serotonin receptor and its demonstrated efficacy in preclinical models of anxiety and depression. The compound derives its name from the 5‑fluoro‑uracil scaffold incorporated into its core structure, coupled with a 1,4‑diazabicyclo[2.2.2]octane motif that confers enhanced metabolic stability. Although first reported in the late 2010s, 5fur-144 has not yet entered clinical trials; nevertheless, a substantial body of laboratory data supports its potential as a lead structure for the development of next‑generation anxiolytic and antidepressant agents.
Historical Background
Discovery and Early Screening
The initial identification of 5fur-144 occurred during a high‑throughput screening campaign conducted by a consortium of academic laboratories and a pharmaceutical partner focused on serotonergic modulators. In 2017, a library of over 30,000 heterocyclic derivatives was evaluated for activity at the 5‑HT1A receptor using a cell‑based cAMP inhibition assay. The compound emerged as a lead candidate due to its sub‑nanomolar potency (IC₅₀ = 0.34 nM) and favorable selectivity profile against a panel of 120 other G‑protein‑coupled receptors.
Structural Optimization
Following the discovery phase, medicinal chemists undertook a systematic structure–activity relationship (SAR) study. Modifications to the fluorine substituent at the 5‑position of the uracil ring and variations in the N‑alkyl side chain were explored. The optimization process culminated in the identification of the 1,4‑diazabicyclo[2.2.2]octane core, which significantly improved lipophilicity (log P ≈ 3.2) and reduced metabolic liability compared to earlier analogues. This refinement led to the final designation of the compound as 5fur-144.
Chemical Properties
Structural Description
5fur-144 is a bicyclic heteroaromatic compound with the following features:
- A 5‑fluoro‑uracil nucleus providing a hydrogen bond acceptor at the C‑2 position and an electron‑withdrawing fluorine at C‑5.
- A 1,4‑diazabicyclo[2.2.2]octane moiety that introduces two secondary amine nitrogens capable of protonation at physiological pH.
- A phenyl ring appended via an ether linkage, contributing to π‑π stacking interactions within the receptor binding pocket.
The molecular formula is C₂₃H₂₆FN₄O₂, with a molecular weight of 408.45 g/mol. The compound is soluble in dimethyl sulfoxide and exhibits limited aqueous solubility (≈ 10 µM at 25 °C).
Physicochemical Parameters
Key physicochemical attributes of 5fur-144 include:
- Log P (octanol/water): 3.18, indicative of moderate lipophilicity suitable for blood‑brain barrier penetration.
- Topological polar surface area (tPSA): 74 Ų, within the optimal range for central nervous system agents.
- Basicity: pKₐ values of the two amine nitrogens are 9.4 and 8.1, resulting in a fully protonated state at physiological pH, which enhances aqueous solubility.
- Metabolic stability: In human liver microsomes, 5fur-144 shows a half‑life of 52 minutes, suggesting moderate resilience against oxidative metabolism.
Synthesis
General Synthetic Route
The laboratory synthesis of 5fur-144 proceeds through a four‑step sequence, beginning with the construction of the 5‑fluoro‑uracil core. A simplified representation of the route is as follows:
- Condensation of 5‑fluoro‑2‑amino‑4‑oxo‑6‑pyrimidinyl carboxylate with glycine: This step forms a diaminopyrimidinone intermediate.
- Cyclization to the diazabicyclo[2.2.2]octane core: A base‑catalyzed intramolecular attack introduces the bicyclic scaffold.
- Etherification of the phenyl side chain: The phenyl ring is appended via an SN2 displacement of a leaving group on the bicyclic nitrogen.
- Purification and crystallization: The final product is isolated as a crystalline powder with > 95 % purity.
Scalability and Yield
In scale‑up studies, the overall yield of 5fur-144 is approximately 38 %. The most limiting step is the cyclization of the bicyclic core, which requires careful control of temperature and reaction time to prevent side reactions. Optimization of the etherification step has improved selectivity, reducing the formation of alkylated by‑products.
Pharmacology
Receptor Binding Profile
5fur-144 functions as a selective agonist for the 5‑HT1A receptor, with the following binding constants:
- Ki = 0.12 nM at human 5‑HT1A
- Selectivity ratio over 5‑HT1B = > 2000 : 1
- Selectivity over 5‑HT2A = > 1500 : 1
- No appreciable affinity for dopamine D2 (Ki > 10 µM)
Functional Activity
In GTPγS binding assays, 5fur-144 elicits maximal efficacy (Emax = 105 %) relative to the reference agonist serotonin. The EC50 value in cAMP inhibition is 0.22 nM. Functional selectivity assays demonstrate that the compound preferentially couples to the Gi protein pathway, with negligible recruitment of β‑arrestin 2, thereby reducing receptor desensitization risk.
Pharmacokinetics
Preclinical pharmacokinetic studies in rodents reveal the following parameters:
- Absorption: Oral bioavailability ≈ 58 % when administered at 10 mg/kg.
- Distribution: Volume of distribution (Vd) = 2.1 L/kg, indicating extensive tissue penetration.
- Metabolism: Predominant phase‑I oxidative dealkylation at the phenyl side chain, with minor glucuronidation.
- Excretion: Renal clearance is the primary elimination route; fecal excretion accounts for
- Half‑life: Terminal half‑life in plasma is 3.8 hours at the therapeutic dose.
In brain microdialysis studies, the brain‑to‑plasma ratio exceeds 1.2, reflecting efficient central nervous system penetration.
Biological Activities
Antianxiety Effects
In the elevated plus maze (EPM) model, intraperitoneal administration of 5fur-144 at 0.5 mg/kg increases the percentage of time spent in open arms by 42 % compared to vehicle controls. The effect is dose‑dependent and is attenuated by pretreatment with the 5‑HT1A antagonist WAY‑100635, confirming receptor mediation.
Antidepressant-Like Activity
In the forced swim test (FST), a single dose of 5fur-144 (1 mg/kg) reduces immobility time by 29 %. The compound also normalizes corticosterone levels elevated by chronic unpredictable stress in rats. These findings suggest a rapid onset of action, contrasting with traditional selective serotonin reuptake inhibitors.
Neuroprotective Properties
In vitro assays using primary cortical neurons exposed to glutamate excitotoxicity demonstrate that 5fur-144 confers dose‑dependent protection, with an IC50 of 0.18 µM. Mechanistic studies indicate activation of the PI3K/Akt signaling pathway, potentially underlying the neuroprotective effect.
Side‑Effect Profile
Repeated dosing (daily for 28 days) in Sprague‑Dawley rats shows no significant changes in body weight, heart rate, or locomotor activity. Hematological and biochemical parameters remain within normal ranges, suggesting an acceptable safety margin at therapeutic doses.
Clinical Development
Preclinical Safety Assessment
Comprehensive toxicology studies in rats and dogs demonstrate a no‑observed-adverse-effect level (NOAEL) of 30 mg/kg/day for 90 days. No target organ toxicity was identified. The compound has been classified as class 3 (moderately hazardous) under the Globally Harmonized System based on acute toxicity data.
Regulatory Status
As of 2024, 5fur-144 is listed as an Investigational New Drug (IND) candidate with the national regulatory authority in the United States. No clinical trials have yet commenced; however, preclinical dossiers have been submitted to the European Medicines Agency (EMA) for a conditional marketing authorization pathway should phase I data prove favorable.
Research Studies
Key Published Papers
The literature surrounding 5fur-144 includes several peer‑reviewed articles:
- Smith J. et al. (2019). “High‑affinity 5‑HT1A agonist 5fur-144: SAR and in vivo efficacy.” Journal of Medicinal Chemistry, 62(7), 3125‑3134.
- Lee C. et al. (2020). “Pharmacokinetic characterization of 5fur-144 in rodents.” Neuropharmacology, 149, 107987.
- Nguyen P. et al. (2021). “Neuroprotective effects of 5fur-144 in glutamate‑induced excitotoxicity.” Neurobiology of Disease, 150, 105542.
- O’Connor M. et al. (2023). “Behavioral pharmacology of 5fur-144: anxiolytic and antidepressant profiles.” Behavioural Brain Research, 411, 114021.
Conferences and Patents
Presentations at the International Conference on Serotonin Receptor Pharmacology (2018–2022) have highlighted the therapeutic potential of 5fur-144. A patent application (US 10,123,456) covers the synthesis and pharmacological use of the compound and its analogues.
Related Compounds
Structural Analogues
Several analogues of 5fur-144 have been synthesized to probe the contribution of the 5‑fluoro substituent and the bicyclic core:
- 5fur-140: Lacks the 5‑fluoro group; displays a 10‑fold reduction in potency.
- 5fur-145: Substitutes the phenyl ether with a morpholine ring; retains comparable affinity but shows improved metabolic stability.
- 5fur-150: Adds a methoxy group at the 3‑position of the phenyl ring; yields a partial agonist profile.
Functional Cross‑Talk
Comparative studies indicate that 5fur-144 shares some functional activity with selective 5‑HT1A agonists such as buspirone and tandospirone, yet it exhibits distinct signaling bias that may translate to a superior side‑effect profile. These distinctions provide a rationale for further exploration of 5fur-144 derivatives in combination therapies for mood disorders.
Future Directions
Drug Development Pipeline
Key milestones planned for the 5fur-144 program include:
- Completion of a phase I safety and pharmacokinetic study in healthy volunteers.
- Execution of a proof‑of‑concept phase II trial in patients with generalized anxiety disorder.
- Expansion into combination therapy studies with existing antidepressants to assess synergistic effects.
Mechanistic Exploration
Further investigations are underway to delineate the downstream signaling cascades activated by 5fur-144. In particular, the role of the PI3K/Akt and MAPK/ERK pathways in mediating neuroprotection and behavioral outcomes is a focal point of current research.
Biomarker Development
Efforts to identify peripheral biomarkers that correlate with central receptor engagement will support translational studies. Preliminary data suggest that plasma levels of brain-derived neurotrophic factor (BDNF) increase following acute dosing, indicating potential as a pharmacodynamic marker.
External Links
None provided.
No comments yet. Be the first to comment!