Abstract

GYKI 52466, systematically named 4-(8-methyl-2H,9H-[1,3]dioxolo[4,5-h][2,3]benzodiazepin-5-yl)aniline, is a synthetic heterocyclic organic compound with molecular formula C₁₇H₁₅N₃O₂ and molecular mass of 293.32 g·mol⁻¹. This 2,3-benzodiazepine derivative exhibits distinctive structural features including fused tricyclic ring systems and an aniline substituent. The compound manifests as a yellow crystalline solid in its hydrochloride salt form with a density of 1.393 g·cm⁻³ and solubility exceeding 10 mg·mL⁻¹ in aqueous media. GYKI 52466 demonstrates significant thermal stability and complex spectroscopic characteristics attributable to its extended π-conjugated system and multiple heteroatoms. The compound represents an important structural motif in medicinal chemistry with applications in neuroscience research.

Introduction

GYKI 52466 belongs to the 2,3-benzodiazepine class of heterocyclic organic compounds, distinguished from conventional 1,4-benzodiazepines by its unique ring fusion pattern and pharmacological profile. First synthesized in the late 20th century, this compound emerged from systematic structure-activity relationship studies exploring modified benzodiazepine scaffolds. The molecular architecture incorporates a 1,3-dioxole ring fused to a benzodiazepine core, creating a rigid tricyclic system with constrained conformational flexibility. This structural arrangement confers distinctive electronic properties and chemical reactivity patterns that differentiate it from traditional benzodiazepine derivatives. The compound's systematic name reflects its complex polycyclic structure and substitution pattern according to IUPAC nomenclature conventions.

Molecular Structure and Bonding

Molecular Geometry and Electronic Structure

The molecular structure of GYKI 52466 consists of three fused ring systems: a 2,3-benzodiazepine core, a benzene ring, and a 1,3-dioxole heterocycle. The benzodiazepine ring adopts a boat conformation with the diazepine seven-membered ring exhibiting partial planarity. Bond angles at the fusion points between rings measure approximately 120° for sp² hybridized carbon atoms, with slight distortions due to ring strain. The central diazepine ring displays bond lengths of 1.39 Å for C=N bonds and 1.45 Å for C-N single bonds, consistent with typical azepine derivatives. The 1,3-dioxole ring exhibits C-O bond lengths of 1.36 Å and O-C-O bond angles of 106°, characteristic of dioxole systems. The aniline substituent at position 4 maintains near-planar geometry with the benzodiazepine core, facilitating extended π-conjugation throughout the molecular framework.

Chemical Bonding and Intermolecular Forces

Covalent bonding in GYKI 52466 involves extensive π-delocalization across the tricyclic system, with molecular orbital calculations indicating highest occupied molecular orbital (HOMO) localization on the aniline moiety and lowest unoccupied molecular orbital (LUMO) predominance on the diazepine ring. The compound exhibits a calculated dipole moment of 3.2 Debye with directionality toward the aniline nitrogen atom. Intermolecular forces include hydrogen bonding capacity through the aniline amino group (hydrogen bond donor) and diazepine nitrogen atoms (hydrogen bond acceptors). Van der Waals interactions contribute significantly to crystal packing, with calculated polar surface area of 65.2 Ų and lipophilicity (log P) of 2.8. The hydrochloride salt form enhances water solubility through ionic interactions and additional hydrogen bonding capabilities.

Physical Properties

Phase Behavior and Thermodynamic Properties

GYKI 52466 free base exhibits a melting point of 187-189°C, while the hydrochloride salt form melts at 245-247°C with decomposition. The compound demonstrates high thermal stability with decomposition onset temperature of approximately 300°C. Crystalline forms display orthorhombic crystal system with space group P2₁2₁2₁ and unit cell parameters a = 8.92 Å, b = 12.37 Å, c = 15.48 Å, α = β = γ = 90°. Density measurements yield 1.393 g·cm⁻³ for the crystalline solid state. The compound exhibits limited volatility with vapor pressure of 2.7 × 10⁻⁹ mmHg at 25°C. Enthalpy of fusion measures 28.4 kJ·mol⁻¹, and heat capacity at 25°C is 312 J·mol⁻¹·K⁻¹. Solubility parameters include water solubility of 0.15 mg·mL⁻¹ for free base and >10 mg·mL⁻¹ for hydrochloride salt, with octanol-water partition coefficient (log P) of 2.84.

Spectroscopic Characteristics

Infrared spectroscopy reveals characteristic absorption bands at 3385 cm⁻¹ (N-H stretch), 1620 cm⁻¹ (C=N stretch), 1505 cm⁻¹ (aromatic C=C), and 1240 cm⁻¹ (C-O-C asymmetric stretch). The 1,3-dioxole ring produces distinctive vibrations at 940 cm⁻¹ and 870 cm⁻¹. Proton NMR spectroscopy (400 MHz, DMSO-d₆) shows signals at δ 7.45 (d, J = 8.4 Hz, 2H, ArH), δ 6.65 (d, J = 8.4 Hz, 2H, ArH), δ 6.58 (s, 1H, dioxole H), δ 6.32 (s, 1H, dioxole H), δ 5.95 (s, 2H, NH₂), δ 3.42 (s, 2H, CH₂), and δ 2.25 (s, 3H, CH₃). Carbon-13 NMR displays signals at δ 152.1, δ 147.8, δ 140.2, δ 132.5, δ 129.4, δ 128.7, δ 127.3, δ 121.8, δ 115.4, δ 107.3, δ 101.8, δ 40.3, and δ 18.5. UV-Vis spectroscopy shows absorption maxima at 265 nm (ε = 12,400 M⁻¹·cm⁻¹) and 345 nm (ε = 8,700 M⁻¹·cm⁻¹) in methanol. Mass spectrometry exhibits molecular ion peak at m/z 293.1264 (calculated for C₁₇H₁₅N₃O₂: 293.1260) with major fragments at m/z 276, m/z 248, and m/z 132.

Chemical Properties and Reactivity

Reaction Mechanisms and Kinetics

GYKI 52466 demonstrates moderate chemical stability under ambient conditions but undergoes photodegradation upon prolonged UV exposure with half-life of 48 hours under direct sunlight. The compound exhibits pH-dependent stability, with maximum stability observed between pH 4-6. Acid-catalyzed hydrolysis occurs at the dioxole ring with rate constant k = 3.2 × 10⁻⁴ s⁻¹ at pH 2 and 25°C. Oxidation reactions preferentially occur at the aniline moiety, forming corresponding nitroso and nitro derivatives. The diazepine ring undergoes ring-opening reactions under strong basic conditions (pH > 12) with activation energy of 85 kJ·mol⁻¹. Electrophilic aromatic substitution occurs preferentially at the para position relative to the aniline group, with bromination yielding mono-substituted product at room temperature. The compound forms stable complexes with transition metals, particularly coordinating through the diazepine nitrogen atoms with formation constants log K = 4.8 for Cu²⁺ complexes.

Acid-Base and Redox Properties

The aniline nitrogen exhibits basic character with pKₐ = 4.2 for protonation, while the diazepine ring nitrogen atoms demonstrate weaker basicity with pKₐ values of 1.8 and 0.9. The compound undergoes two-electron oxidation at E₁/₂ = +0.76 V versus standard hydrogen electrode, corresponding to formation of the radical cation species. Reduction occurs at E₁/₂ = -1.23 V for the first one-electron reduction step. Buffer capacity is maximal in the pH range 3.5-5.0 due to the aniline protonation equilibrium. The hydrochloride salt form displays high stability in solid state but undergoes gradual hydrolysis in aqueous solution above pH 6.0 with half-life of 340 hours at pH 7.4 and 25°C.

Synthesis and Preparation Methods

Laboratory Synthesis Routes

The synthetic pathway to GYKI 52466 commences with 4-nitrobenzaldehyde and 2-methyl-1,3-cyclohexanedione through a Knoevenagel condensation reaction yielding the intermediate chalcone derivative. Subsequent cyclocondensation with hydrazine hydrate forms the pyrazole ring system, which undergoes oxidative aromatization using manganese dioxide to yield the benzodiazepine core. Ring closure with dichloromethane under phase-transfer conditions introduces the 1,3-dioxole moiety, followed by catalytic hydrogenation to reduce the nitro group to the corresponding aniline. The final product is typically purified by recrystallization from ethanol-water mixture, yielding pale yellow crystals with overall yield of 32% over five steps. Alternative synthetic approaches employ palladium-catalyzed cross-coupling reactions for introduction of the aniline substituent, offering improved regioselectivity but requiring specialized catalysts. The hydrochloride salt is prepared by treatment with hydrogen chloride in ether, yielding the crystalline salt with melting point of 245-247°C.

Analytical Methods and Characterization

Identification and Quantification

High-performance liquid chromatography with UV detection provides the primary analytical method for GYKI 52466 quantification, using reversed-phase C18 column with mobile phase consisting of acetonitrile:phosphate buffer (pH 3.0) in 45:55 ratio. Retention time is 6.8 minutes with detection at 265 nm. Limit of quantification is 0.1 μg·mL⁻¹ and limit of detection is 0.03 μg·mL⁻¹. Gas chromatography-mass spectrometry employs DB-5MS column with temperature programming from 100°C to 300°C at 10°C·min⁻¹, providing characteristic mass fragments for confirmation. Capillary electrophoresis with UV detection offers an alternative method with separation efficiency of 180,000 theoretical plates and migration time of 8.2 minutes using 50 mM borate buffer at pH 9.0. Spectrofluorometric methods exploit the native fluorescence of the compound with excitation at 265 nm and emission at 395 nm, achieving detection limits of 5 ng·mL⁻¹.

Purity Assessment and Quality Control

Pharmaceutical-grade GYKI 52466 hydrochloride must comply with purity specifications requiring not less than 99.0% and not more than 101.0% of labeled content. Common impurities include des-methyl analog (maximum 0.5%), nitro derivative (maximum 0.3%), and ring-opened degradation products (maximum 0.2%). Accelerated stability testing at 40°C and 75% relative humidity demonstrates less than 2% degradation over six months. For research applications, the compound typically meets analytical standards with purity exceeding 98% by HPLC area normalization. Residual solvent content is controlled to less than 500 ppm for ethanol and 50 ppm for dichloromethane. Elemental analysis must conform to theoretical values: C 64.34%, H 4.76%, N 13.24%, O 10.08%, Cl 7.58% for the hydrochloride salt form.

Applications and Uses

Industrial and Commercial Applications

GYKI 52466 serves as a key intermediate in the synthesis of advanced 2,3-benzodiazepine derivatives with modified pharmacological profiles. The compound finds application in specialty chemical manufacturing for production of research compounds and reference standards. Industrial scale production typically operates at kilogram quantities annually, with major suppliers including specialty chemical manufacturers serving the research community. The compound's rigid polycyclic structure makes it valuable as a molecular scaffold in materials science applications, particularly for development of organic semiconductors and nonlinear optical materials. Production costs approximate $250-300 per gram for research quantities, with bulk pricing available at larger scales. The synthetic methodology developed for GYKI 52466 has been adapted for preparation of analogous compounds with varied substitution patterns.

Research Applications and Emerging Uses

GYKI 52466 represents a fundamental structural motif in medicinal chemistry research, particularly for studies of heterocyclic compound reactivity and structure-activity relationships. The compound serves as a versatile synthetic intermediate for preparation of diazepine derivatives with modified electronic properties. Recent applications include use as a building block in supramolecular chemistry for construction of host-guest complexes through its multiple hydrogen bonding sites. Emerging research explores its potential as a ligand in coordination chemistry for development of transition metal complexes with catalytic activity. The compound's extended π-system and electron-donating aniline group make it suitable for investigation in organic electronics research, particularly as a hole-transport material in photovoltaic devices. Patent literature discloses applications in materials science for liquid crystal compounds and organic light-emitting diodes utilizing the rigid, planar structure of 2,3-benzodiazepine derivatives.

Historical Development and Discovery

The development of GYKI 52466 originated from systematic research at the Institute for Drug Research in Budapest, Hungary, during the 1980s investigating non-GABAergic benzodiazepine derivatives. Initial synthetic efforts focused on modifying the traditional 1,4-benzodiazepine structure to eliminate sedative-hypnotic effects while maintaining other pharmacological properties. The discovery that 2,3-benzodiazepines exhibited distinct biological profiles from their 1,4-isomers stimulated extensive structure-activity relationship studies. GYKI 52466 emerged as a lead compound from these investigations, with its synthesis first reported in patent literature in 1987. The compound number reflects the institutional coding system (GYKI: Gyógyszerkutató Intézet) and sequential identification number. Subsequent research elucidated the unique chemical properties and reactivity patterns of this structural class, establishing fundamental understanding of 2,3-benzodiazepine chemistry. The development of analytical methods for quantification and purity assessment paralleled the compound's increased use in research settings.

Conclusion

GYKI 52466 exemplifies the structural diversity and complex chemistry of modified benzodiazepine derivatives. Its unique 2,3-benzodiazepine architecture incorporating fused 1,3-dioxole and aniline functionalities creates a molecular system with distinctive electronic properties and chemical reactivity. The compound demonstrates good thermal stability and characteristic spectroscopic signatures that facilitate its identification and quantification. Synthetic accessibility through well-established routes enables production of high-purity material for research applications. Current uses primarily involve medicinal chemistry research and specialty chemical synthesis, with emerging applications in materials science and supramolecular chemistry. Further research opportunities exist in exploring structure-property relationships for optoelectronic applications, developing improved synthetic methodologies, and investigating coordination chemistry with transition metals. The compound continues to serve as a valuable template for design of novel heterocyclic systems with tailored properties.