Abstract

Nordinone, systematically named (3b''R'',9a''R'',9b''S'',10''R'')-10-hydroxy-1,1,9a-trimethyl-1,2,3,3b,4,5,8,9,9a,9b,10,11-dodecahydro-7''H''-cyclopenta[''a'']phenanthren-7-one, is a naturally occurring steroidal compound with the molecular formula C₂₀H₂₈O₂. This modified androstane derivative features a characteristic 4,13-dien-3-one configuration and an 11α-hydroxy substituent. The compound exhibits a molecular mass of 300.44 g·mol⁻¹ and demonstrates significant structural complexity with four chiral centers. Nordinone manifests limited solubility in aqueous media but dissolves readily in organic solvents including ethanol, methanol, and chloroform. The compound's unique structural features contribute to its distinctive chemical behavior and potential applications in steroid chemistry research.

Introduction

Nordinone represents a structurally modified steroid belonging to the 18-norandrostane series, specifically classified as 11α-hydroxy-17,17-dimethyl-18-norandrosta-4,13-dien-3-one. This organic compound was first isolated as a fungal metabolite from Monocillium nordinii, which accounts for its common name. The compound's discovery expanded the known structural diversity of naturally occurring steroids and provided insights into fungal biosynthetic pathways. Nordinone occupies a significant position in steroid chemistry due to its unusual 18-nor configuration combined with both 4-en-3-one and 13-en moieties, creating a conjugated system that influences its electronic properties and reactivity patterns. The presence of multiple functional groups—ketone, hydroxyl, and diene—within a rigid steroidal framework makes this compound particularly interesting for structure-activity relationship studies and synthetic modification work.

Molecular Structure and Bonding

Molecular Geometry and Electronic Structure

Nordinone possesses a tetracyclic steroidal framework based on the gonane nucleus with significant modifications including the absence of the C-18 methyl group (18-nor configuration) and additional methyl groups at C-17. The molecular geometry adopts the characteristic folded conformation of steroidal compounds with ring A existing in a half-chair conformation, rings B and C in chair conformations, and ring D in an envelope conformation. X-ray crystallographic analysis reveals bond lengths typical for steroidal systems: C-C bonds range from 1.50 Å to 1.54 Å, C-O bonds measure approximately 1.22 Å for the ketone and 1.43 Å for the hydroxyl group, and C=C bonds in the diene system measure 1.34 Å.

The electronic structure features significant conjugation between the 4-en-3-one system (π-π conjugation) and the isolated 13-en moiety, creating two distinct chromophores. Molecular orbital calculations indicate highest occupied molecular orbitals localized primarily on the diene systems and oxygen lone pairs, while the lowest unoccupied molecular orbitals concentrate on the π* orbitals of the enone system. The compound's four chiral centers at positions 3b, 9a, 9b, and 10 create specific stereochemical constraints that influence both molecular geometry and electronic distribution. The 11α-hydroxy group adopts an axial orientation in the chair conformation of ring C, creating 1,3-diaxial interactions with neighboring hydrogen atoms.

Chemical Bonding and Intermolecular Forces

Covalent bonding in nordinone follows typical patterns for organic compounds with carbon-carbon single bonds (bond energy approximately 347 kJ·mol⁻¹), carbon-carbon double bonds (bond energy approximately 611 kJ·mol⁻¹), carbon-oxygen double bonds (bond energy approximately 799 kJ·mol⁻¹), and carbon-oxygen single bonds (bond energy approximately 358 kJ·mol⁻¹). The molecular dipole moment measures approximately 3.2 Debye, primarily resulting from the polarized carbonyl group and hydroxyl group. Intermolecular forces include van der Waals interactions throughout the hydrocarbon framework, dipole-dipole interactions involving the carbonyl and hydroxyl groups, and potential hydrogen bonding through the 11α-hydroxy group as both donor and acceptor.

The compound exhibits moderate polarity with calculated octanol-water partition coefficient (log P) of approximately 2.8, indicating greater affinity for organic phases. Crystal packing arrangements demonstrate hydrogen bonding between hydroxyl groups of adjacent molecules with O···O distances of approximately 2.78 Å, forming extended chains in the solid state. Van der Waals interactions between methyl groups and hydrocarbon regions contribute significantly to crystal stability, with typical carbon-carbon intermolecular distances of 3.5-4.0 Å.

Physical Properties

Phase Behavior and Thermodynamic Properties

Nordinone presents as a white to off-white crystalline solid at room temperature. The compound melts at 218-220 °C with decomposition, as the enone system undergoes thermal degradation before reaching a clear melting point. Crystallization from ethanol yields orthorhombic crystals belonging to space group P2₁2₁2₁ with unit cell parameters a = 7.82 Å, b = 12.35 Å, c = 18.91 Å, and α = β = γ = 90°. The calculated density is 1.18 g·cm⁻³ at 20 °C.

Thermodynamic parameters include heat of fusion of 28.5 kJ·mol⁻¹ and heat of vaporization of 98.3 kJ·mol⁻¹ (estimated). The compound sublimes at reduced pressure (0.1 mmHg) at temperatures above 150 °C. Specific heat capacity measures 1.32 J·g⁻¹·K⁻¹ at 25 °C. Solubility characteristics demonstrate limited aqueous solubility (0.85 mg·mL⁻¹ at 25 °C) but good solubility in polar organic solvents: ethanol (45 mg·mL⁻¹), methanol (52 mg·mL⁻¹), chloroform (68 mg·mL⁻¹), and acetone (58 mg·mL⁻¹). The refractive index of crystalline nordinone is 1.58 at 589 nm and 20 °C.

Spectroscopic Characteristics

Infrared spectroscopy reveals characteristic absorption bands at 3412 cm⁻¹ (O-H stretch), 1665 cm⁻¹ (C=O stretch, conjugated), 1618 cm⁻¹ and 1587 cm⁻¹ (C=C stretch, diene system), and 1452 cm⁻¹ (C-H bend, methyl groups). Proton nuclear magnetic resonance spectroscopy (¹H NMR, 400 MHz, CDCl₃) shows signals at δ 5.92 (s, 1H, H-4), δ 5.78 (d, J = 9.8 Hz, 1H, H-14), δ 5.65 (d, J = 9.8 Hz, 1H, H-15), δ 4.12 (m, 1H, H-11), δ 2.45-2.35 (m, 2H, H-2), δ 1.18 (s, 3H, 17-CH₃), δ 1.12 (s, 3H, 17-CH₃), δ 0.98 (s, 3H, 10-CH₃).

Carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR, 100 MHz, CDCl₃) displays characteristic signals at δ 199.5 (C-3), δ 171.2 (C-13), δ 153.6 (C-4), δ 132.8 (C-14), δ 125.7 (C-5), δ 121.3 (C-15), δ 71.8 (C-11), δ 55.4 (C-9), δ 48.7 (C-10), δ 44.3 (C-17), δ 39.8 (C-12), δ 37.5 (C-1), δ 35.6 (C-7), δ 33.2 (C-2), δ 28.4 (C-16), δ 27.9 (17-CH₃), δ 27.3 (17-CH₃), δ 24.5 (C-6), δ 22.7 (C-8), δ 18.9 (10-CH₃). Ultraviolet-visible spectroscopy demonstrates absorption maxima at 242 nm (ε = 12,500 M⁻¹·cm⁻¹) and 290 nm (ε = 4,800 M⁻¹·cm⁻¹) in ethanol, corresponding to π→π* transitions of the enone and diene systems respectively.

Chemical Properties and Reactivity

Reaction Mechanisms and Kinetics

Nordinone demonstrates reactivity characteristic of both enones and isolated alkenes within a steroidal framework. The 4-en-3-one system undergoes Michael addition reactions with nucleophiles at the β-carbon (C-4) with second-order rate constants of approximately 0.15 M⁻¹·s⁻¹ for thiol additions in ethanol at 25 °C. The carbonyl group at C-3 participates in standard ketone reactions including reduction with sodium borohydride (yielding the 3β-hydroxy derivative), oxime formation, and hydrazone formation. The 13,14-double bond undergoes electrophilic addition reactions with bromine and other halogens with rate constants approximately 20-fold slower than typical alkenes due to steric hindrance from the steroidal framework.

The 11α-hydroxy group exhibits secondary alcohol reactivity, undergoing oxidation with Jones reagent to the corresponding ketone at rates comparable to other secondary alcohols (k = 0.08 M⁻¹·s⁻¹ at 25 °C). Esterification occurs with acid chlorides and anhydrides under standard conditions. Thermal decomposition begins at temperatures above 200 °C through retro-ene reactions and enone polymerization pathways. The compound demonstrates stability in neutral and acidic conditions (pH 3-7) but undergoes dehydration under strongly acidic conditions to form the corresponding 11,12-dehydro derivative.

Acid-Base and Redox Properties

The 11α-hydroxy group exhibits weak acidity with pKₐ of approximately 15.2 in water, comparable to other secondary alcohols. The compound shows no basic character under normal conditions. Redox properties include reduction potentials of -1.32 V (vs. SCE) for the enone system in acetonitrile, measured by cyclic voltammetry. The hydroxyl group oxidizes at +0.95 V (vs. SCE) under the same conditions. Nordinone demonstrates stability toward mild oxidizing agents including atmospheric oxygen but undergoes oxidation with strong oxidizing agents such as potassium permanganate and chromium trioxide.

The compound maintains stability in reducing environments including sodium borohydride and lithium aluminum hydride, with only the carbonyl group undergoing reduction. Hydrogenation with catalytic platinum oxide reduces both the 4,5-double bond and the 13,14-double bond sequentially, with the 4,5-double bond reducing first due to less steric hindrance. Half-wave potentials for polarographic reduction are -1.05 V and -1.87 V (vs. mercury pool electrode) corresponding to the two reducible double bonds.

Synthesis and Preparation Methods

Laboratory Synthesis Routes

Laboratory synthesis of nordinone typically begins with more readily available steroid precursors. The most efficient route starts with 17,17-dimethylandrosta-4,13-dien-3-one, which undergoes microbial oxidation using Rhizopus arrhizus to introduce the 11α-hydroxy group with approximately 65% yield and high stereoselectivity. The fermentation process requires 48-72 hours at 28 °C in a glucose-peptone medium with aeration. Chemical synthesis approaches involve epoxidation of the 11,12-double bond in appropriate precursors followed by acid-catalyzed opening of the epoxide to yield the 11α-hydroxy configuration.

Alternative synthetic routes employ selenium dioxide oxidation of 17,17-dimethylandrost-4-en-3-one to introduce the 13,14-double bond, followed by microbial or chemical hydroxylation at C-11. Purification typically involves column chromatography on silica gel with ethyl acetate/hexane gradients, followed by recrystallization from ethanol/water mixtures. The overall yield for multi-step syntheses ranges from 15-25%, with the microbial hydroxylation step often being yield-limiting. Characterization of synthetic material requires comparison with natural nordinone using chromatographic and spectroscopic methods to ensure identity and purity.

Analytical Methods and Characterization

Identification and Quantification

Chromatographic methods provide the primary means of nordinone identification and quantification. High-performance liquid chromatography employing C18 reverse-phase columns with methanol-water mobile phases (70:30 v/v) achieves baseline separation with retention time of 12.3 minutes at flow rate of 1.0 mL·min⁻¹. Detection utilizes ultraviolet absorption at 242 nm with limit of detection of 0.1 μg·mL⁻¹ and limit of quantification of 0.3 μg·mL⁻¹. Gas chromatography-mass spectrometry employing DB-5MS columns shows characteristic fragmentation patterns including m/z 300 (molecular ion), m/z 285 (M⁺-CH₃), m/z 257 (M⁺-C₃H₇), and m/z 122 (ring A fragment).

Thin-layer chromatography on silica gel GF₂₅₄ plates with ethyl acetate/cyclohexane (50:50 v/v) development yields Rf value of 0.45 with detection by ultraviolet quenching at 254 nm or charring with sulfuric acid. Capillary electrophoresis methods using borate buffer at pH 9.2 provide separation with migration time of 8.7 minutes and detection at 242 nm. Quantitative analysis demonstrates linear response from 0.5-100 μg·mL⁻¹ with correlation coefficients exceeding 0.999 and relative standard deviation of 1.8% for replicate injections.

Purity Assessment and Quality Control

Purity assessment typically employs orthogonal methods including chromatography, spectroscopy, and melting point determination. Common impurities include dehydration products (11,12-dehydro derivative), over-oxidation products (11-keto derivative), and starting materials from synthetic routes. Pharmaceutical quality control specifications require minimum purity of 98.0% by HPLC area normalization, with individual impurities limited to not more than 0.5% and total impurities not more than 2.0%. Residual solvent analysis by gas chromatography must meet ICH guidelines with limits of 5000 ppm for ethanol and 1000 ppm for chloroform.

Spectroscopic purity criteria include ultraviolet absorbance ratios A₂₄₂/A₂₉₀ of 2.58-2.62 and infrared spectrum matching reference spectrum with tolerance of ±5 cm⁻¹ for major peaks. Melting point range must not exceed 3 °C for purified material. Stability studies indicate no significant degradation under accelerated conditions (40 °C/75% RH) for three months when protected from light and stored in sealed containers. Long-term stability requires storage at -20 °C under nitrogen atmosphere for extended periods.

Applications and Uses

Industrial and Commercial Applications

Nordinone serves primarily as a chemical intermediate in steroid synthesis and as a reference compound in analytical chemistry. The compound's unique structure with both 4-en-3-one and 13-en systems provides a versatile platform for chemical modification, particularly for introducing additional functionality into the steroid nucleus. Pharmaceutical research utilizes nordinone as a starting material for synthesizing novel steroid analogs with potential biological activity. The compound finds application in chromatographic method development as a test analyte for reverse-phase systems due to its intermediate polarity and good detectability.

Specialty chemical manufacturers employ nordinone as a building block for creating steroidal liquid crystals and other advanced materials with specific molecular architectures. Research-scale production meets demand from academic and industrial laboratories investigating steroid chemistry and metabolism. Market size remains limited with annual production estimated at 100-200 grams worldwide, primarily supplied by specialty chemical manufacturers. Production costs remain high due to the multi-step synthesis and purification requirements, with current pricing approximately $500-800 per gram for research quantities.

Research Applications and Emerging Uses

Research applications focus primarily on nordinone's utility as a model compound for studying steroidal conjugation systems and stereoelectronic effects. The compound serves as a substrate for investigating microbial transformation reactions, particularly hydroxylation patterns by various fungal species. Materials science research explores nordinone derivatives as potential components of molecular assemblies and supramolecular structures due to the compound's rigid framework and functional group versatility.

Emerging applications include use as a chiral template in asymmetric synthesis and as a molecular probe for studying enzyme-active site geometries through analog synthesis. Recent patent activity describes nordinone derivatives as potential ligands for nuclear receptors and as scaffolds for drug discovery programs targeting protein-protein interactions. The compound's unique combination of structural features continues to inspire synthetic creativity and exploration of novel chemical space within steroid chemistry.

Historical Development and Discovery

Nordinone was first isolated and characterized in 1973 from cultures of the fungus Monocillium nordinii during systematic screening of microorganisms for novel steroid metabolites. The discovery resulted from collaboration between mycologists and natural products chemists investigating fungal transformation of steroidal compounds. Initial structure elucidation employed classical chemical degradation combined with emerging spectroscopic techniques including early 100 MHz NMR instrumentation and mass spectrometry.

The compound's structure was confirmed through chemical correlation with known steroids and X-ray crystallographic analysis of derivatives. The discovery expanded understanding of fungal steroid metabolism and demonstrated the capability of microorganisms to produce structurally complex steroid derivatives through oxidative metabolism. Subsequent research in the 1980s developed synthetic routes to nordinone, enabling more detailed study of its chemical properties and potential applications. The 1990s saw increased interest in nordinone derivatives as tools for studying steroid-receptor interactions and as potential therapeutic agents.

Conclusion

Nordinone represents a structurally unique steroid with significant interest for fundamental chemistry research and potential applications in materials science and pharmaceutical development. The compound's combination of 18-nor configuration, 4,13-dien-3-one system, and 11α-hydroxy group creates distinctive electronic properties and reactivity patterns that differentiate it from conventional steroids. Current research continues to explore novel synthetic methodologies for nordinone and its derivatives, particularly those enabling selective functionalization of the complex molecular framework.

Future research directions include development of more efficient synthetic routes, exploration of nordinone's potential as a chiral building block, and investigation of its derivatives as molecular probes for biological systems. The compound's structural features suggest potential for creating novel materials with specific molecular recognition properties and for developing new stereoselective catalysts. Nordinone continues to serve as an important reference compound in steroid chemistry and a inspiration for synthetic creativity in molecular design.