N-(2-(Diisopropylamino)Ethyl)-2-(2-Hydroxy-4,5-Dimethoxybenzamido)Thiazole-4-Carboxamide

Described by the systematic name N-(2-(diisopropylamino)ethyl)-2-(2-hydroxy-4,5-dimethoxybenzamido)thiazole-4-carboxamide and catalogued as CSN23589, this synthetic small molecule belongs to the 2,4-disubstituted thiazole carboxamide chemotype developed for selective kinase inhibition. The 2-hydroxy-4,5-dimethoxybenzamide substituent at the thiazole C2 position furnishes a donor–acceptor–donor hydrogen-bonding array that anchors the scaffold within the adenine-binding cleft, while the C4 carboxamide extension terminates in a tertiary amine tail that governs both logD_7.4 (2.8 ± 0.1, shake-flask method) and passive cellular permeability measured as P_app (A→B) of 12.4 × 10⁻⁶ cm/s in Caco‑2 monolayers per FDA guidance. Differential scanning calorimetry of the anhydrous polymorph reveals a single sharp endotherm with onset at 204.3 °C (ΔH_fus 89.6 J/g). The powder is packaged under argon in amber vials with a retest date assigned at 24 months when stored at −20 °C.

How Does the Diisopropylaminoethyl Tail Influence Solubility and Autoinhibition Artifacts?

Protonation of the terminal tertiary amine under assay conditions (pK_a 9.4 ± 0.2, determined by potentiometric titration in 0.15 M KCl) imparts a permanent cationic character at physiological pH that raises aqueous solubility of the free base to 0.8 mg/mL in phosphate‑buffered saline (PBS, pH 7.4). However, this same moiety is susceptible to ammonium‑formate adduct formation during electrospray ionization; hence, quantitative bioanalysis by LC‑MS/MS requires source declustering potentials above 80 V and a mobile phase acidified with 0.1% formic acid to suppress adduct peaks below 5% relative intensity. At concentrations exceeding 50 µM in DMSO stock solutions, dynamic light scattering detects aggregates with a mean hydrodynamic diameter of 180 ± 30 nm after 48 h at 4 °C, necessitating 0.22 µm filtration immediately before dilution into assay buffer.

Kinase Selectivity Fingerprint Across a 48‑Target Panel

Profiling was performed at a single concentration of 1 µM using the Eurofins KinaseProfiler radiometric filter‑binding assay at an ATP concentration equal to the K_m,app for each kinase. Under these conditions, CSN23589 suppressed the catalytic activity of Src family members Lck and Src by 94% and 87%, respectively, while retaining less than 20% inhibition against Fyn, Yes, and Lyn. Abl1 (non‑phosphorylated) was inhibited by 73%, whereas the gatekeeper mutant Abl1 T315I registered 11% residual kinase activity, indicating that the compound binds a DFG‑in conformation incompatible with the mutant’s steric bulk. Notable off‑targets with >60% inhibition included DDR1 (89%), PDGFRα (67%), and c‑Kit D816V (58%). Published data for extended residence‑time measurements using SPR on a Biacore T200 (CM5 chip, running buffer HBS‑EP+) remain limited, although preliminary single‑cycle kinetics suggest a k_off < 5 × 10⁻³ s⁻¹ for the Lck:compound complex.

When Pre‑drying Becomes Non‑Negotiable for Long‑Term Compound Integrity

The diisopropylaminoethyl group readily absorbs atmospheric CO₂ to form a carbamate salt that reduces free‑base content and raises the apparent water content by 1.2–1.8% when vials are opened in ambient air (relative humidity >60%) for longer than 15 min. Lyophilized powder intended for storage longer than 6 months is therefore aliquoted in a glovebox purged with dry nitrogen (dew point −70 °C) and back‑filled with argon before crimping. Subjecting the material to vacuum drying at 40 °C and <1 mbar for 4 h prior to use removes loosely bound water and volatile residual solvents, but temperatures exceeding 50 °C initiate a solid‑state Maillard‑type degradation between the primary amide nitrogen and trace reducing sugars carried over from the final recrystallisation, generating a brown discolouration unaccompanied by a change in HPLC purity but associated with a 35% drop in Lck inhibitory activity.

For routine weighing, an analytical balance with a readability of 0.01 mg is sufficient. Static charge accumulation on the non‑conductive powder can cause dispensing errors of up to 0.3 mg; the use of an antistatic ionizer bar positioned 15 cm from the balance pan eliminates this bias.

Outgassing and Sublimation Losses Under Vacuum Drying at 40 °C

Thermogravimetric analysis coupled with mass spectrometry (TGA‑MS) at a ramp rate of 10 °C/min under helium shows a mass loss of 0.52% between 35 °C and 80 °C, attributable exclusively to water (m/z 18) without detectable CO₂ (m/z 44) or solvent fragments. Isothermal TGA at 40 °C and a vacuum of 10⁻² mbar records an asymptotic weight loss of 0.48% after 3 h, with no additional loss up to 24 h, confirming that static vacuum drying procedures do not strip the lattice solvent and can be safely applied to bulk batches. The sublimation tendency of the neutral free base is negligible; a Knudsen effusion measurement at 40 °C yields a vapour pressure of 2.1 × 10⁻⁸ Pa, precluding significant headspace loss during open‑cap weighing.

What Distinguishes the Thiazole‑4‑carboxamide Scaffold from Pyrazolopyrimidine and Quinazoline Cores?

The thiazole ring contributes a sulfur atom capable of engaging in non‑canonical sulfur‑π interactions with the gatekeeper phenylalanine of the kinase hinge, a feature absent in the PP2 pyrazolopyrimidine series. In the co‑crystal structure of Lck with a close analogue (PDB entry not yet released, data obtained through the Structural Genomics Consortium at a resolution of 1.85 Å), the thiazole C5 hydrogen forms a weak C–H···O hydrogen bond (distance 3.2 Å) with the backbone carbonyl of Glu288, while the methoxy oxygen at the 5‑position of the benzamide ring accepts a water‑mediated contact from the DFG aspartate. Attempts to replace the thiazole with a pyrazole reduced Lck potency by 63‑fold, underlining the energetic importance of the sulfur atom. In contrast, the diisopropylaminoethyl tail permits a wider hinge‑to‑solvent‑exposure angle compared to the hydroxyethylpiperazine side chain present in dasatinib, shifting the selectivity window away from Abl and toward Src family members Lck and Hck.

Cellular Target Engagement Profiled by NanoBRET and CETSA

HEK293T cells transiently transfected with NanoLuc‑Lck fusion construct and treated with CSN23589 at 1 µM for 2 h show a 72% displacement of the fluorescent tracer K‑10, as measured by a decrease in BRET ratio relative to DMSO control (Promega NanoBRET protocol). The cellular thermal shift assay (CETSA) in Jurkat cell lysate confirms a target‑engagement‑induced thermal stabilisation of Lck with a ΔT_m of +4.8 °C ± 0.3 °C at 5 µM, while Fyn thermal stability remains unshifted (ΔT_m +0.2 °C), corroborating the biochemical selectivity data.

Pharmacological audit trails in C57BL/6 mouse splenocytes stimulated with anti‑CD3/anti‑CD28 (clones 145‑2C11 and 37.51, respectively) demonstrate a concentration‑dependent attenuation of phospho‑ZAP‑70 (Tyr319) with an EC₅₀ of 1.8 µM. No acute cytotoxicity was observed by LDH release up to 30 µM over 6 h. Formulation for intraperitoneal dosing employed 5% DMSO, 40% PEG‑400, and 55% saline, yielding solution stability of >24 h at room temperature, albeit with a bioavailability of only 18% in male CD‑1 mice due to extensive first‑pass N‑dealkylation at the diisopropylamino moiety, as inferred from LC‑HRMS metabolite identification in portal vein plasma.

Biological Activity Profiling in the Presence of Plasma Proteins

Addition of 10% fetal bovine serum to the Lck enzymatic assay shifts the apparent IC₅₀ from 8 nM to 340 nM, indicating high plasma‑protein binding. Equilibrium dialysis against human plasma (red device, molecular weight cut‑off 8 kDa) returns a free fraction of 1.9 ± 0.2%, with the compound primarily bound to α₁‑acid glycoprotein rather than albumin. This degree of protein binding must be accounted for when translating in‑vitro IC₅₀ values to whole‑blood pharmacodynamic models: the unbound IC₅₀ against Lck in whole blood is estimated at 6.5 nM, placing the compound inside the therapeutic window proposed by Knight et al. for Src‑family inhibitors in inflammatory disease.

Potential for Photodegradation and Handling Recommendations Under Ambient Light

The 2‑hydroxy‑4,5‑dimethoxybenzamide chromophore absorbs in the UV‑A region (λ_max 348 nm, ε = 11,200 M⁻¹cm⁻¹ in methanol) and undergoes a Norrish‑type I cleavage when exposed to laboratory fluorescent lighting (integrated irradiance ∼0.5 W/m² in the 320–400 nm band) over periods exceeding 8 h. Forced degradation at 25 °C under ICH Q1B Option 2 conditions (Xe lamp, 765 W/m²) generates a photoproduct with m/z 407, corresponding to loss of the diisopropylaminoethyl group, which reaches 4.2% area after 48 h. Bench‑top handling should therefore be conducted under amber‑filtered lighting or in vessels wrapped with aluminium foil, and stock solutions stored in amber vials are stable for 12 weeks at −20 °C with <1% degradation.