1-[[[2-(Dimethyl-Amino)Ethyl]-1H-Indol-5-Yl]Methyl]Sulfonyl]Pyrrolidine Malate Detailed Information, Properties, Uses & Safety

Almotriptan malate compressed into immediate-release tablet cores on a Korsch XL 400 rotary press at 40–80 rpm routinely encounters weight variability exceeding ±3.0% when direct-compression blends drop below 80 mg total core mass. This behavior, documented across multiple commercial batches for the 12.5 mg label claim (equivalent to 17.5 mg almotriptan malate), originates from the needle-like habit of unmilled API crystals exhibiting a Hausner ratio consistently above 1.45 and Carr’s index greater than 28%. Manufacturers targeting a USP ‹905› acceptance value ≤ 15.0 for content uniformity therefore default to roller-compacted granules processed on an Alexanderwerk WP 120 with a roll force of 8–12 kN/cm and a screen size of 1.0 mm. The final blend is encapsulated within a microcrystalline cellulose–lactose monohydrate–sodium starch glycolate matrix, with magnesium stearate limited to 0.75% w/w applied via external lubrication to avoid dissolution slowing observed when the lubricant contact time exceeds 3 min in a bin blender. Compendial compliance requires conformance to Ph. Eur. monograph 01/2024:2709 and USP Almotriptan Malate Tablets, both mandating dissolution testing in 900 mL of 0.1 N hydrochloric acid at 50 rpm paddle speed, with a Q value of 80% at 30 min. Terminal sterilization is not applicable; instead, the core is film-coated with an Opadry® II yellow system applying an approximate 3.0% weight gain, and the finished dosage form is packaged in PVC/PVDC-aluminium blisters with a desiccant for markets where ICH climatic zone IVb ( 30°C/75% RH ) long-term storage conditions are mandated.

Why are lyophilizates preferred for patients with migraine-induced nausea?

Gastric stasis during a migraine attack delays disintegration and absorption of conventional film-coated tablets, a limitation addressed by oral lyophilizates that disintegrate in less than 5 s on the tongue without water. Almotriptan malate is incorporated into a freeze-dried matrix at a unit dose of 12.5 mg almotriptan base, identical to the tablet strength, because the pre-gastric absorption window does not compensate for a dose reduction. The manufacturing process begins with a bulk aqueous solution containing 2.5% w/w API, gelatin 3.0% w/w as structural excipient, mannitol 2.0% w/w as cryoprotectant, and sucralose 0.05% w/w as sweetener, dispensed into pre-formed PVC/PVdC blister pockets at 1.0 mL per cavity. The filled blisters are frozen on a shelf ramped from +5°C to −45°C at a rate of 1.0°C/min, then primary dried for 12 h at 0.2 mbar with a shelf temperature of −10°C, followed by secondary drying at 30°C for 4 h to reduce residual moisture below 2.0%. The resulting lyophilicate achieves a specific surface area in excess of 2.5 m²/g as determined by BET nitrogen adsorption, correlating with the sub- 5 s disintegration time tested per Ph. Eur. test 2.9.1 using 5 mL water at 37°C. Full compliance with the FDA Guidance for Industry “Orally Disintegrating Tablets” ( 2008 ) and the ICH Q8(R2) design-space verification is expected, with the process analytical technology (PAT) tool for lyo-chamber mass spectrometry enabling real-time moisture endpoint determination. Terminal packaging requires aluminium lidding foil with a peel force of 15–25 N per 15 mm strip width, and the finished product is assigned a shelf-life of 36 months when stored at 25°C as supported by long-term stability data in ICH Zone II conditions.

Almotriptan malate monographs curate a dedicated reference standard that must meet the “CRS” (Chemical Reference Substance) purity designation of ≥99.5% (anhydrous, salt-corrected basis) as verified by mass-balance analysis incorporating HPLC and thermogravimetric analysis. This substance is dispensed into 50 mg or 100 mg amber-glass vials under a nitrogen blanket, sealed with butyl-rubber stoppers, and distributed with a certificate listing the assigned content of ±0.05 mg per vial based on quantitative ¹H NMR at 600 MHz versus a certified internal standard of maleic acid. Official dissolution and purity system-suitability protocols require a working standard solution at a concentration of 0.1 mg/mL in mobile phase, prepared on the day of use, filtered through a 0.22 μm PVDF syringe filter, and injected at a volume of 10 μL onto a 150 × 4.6 mm C18 column ( 5 μm particle size) maintained at 30°C. Batch release of the reference standard is governed by ISO 17034:2016 for reference material producers, and the material is traceable to the Ph. Eur. CRS batch and the WHO International Chemical Reference Substance program. Long-term stability monitoring at 2–8°C and −20°C over 48 months indicates no detectable degradation when humidity ingress is maintained below 100 ppm via continuous positive-pressure dry-nitrogen storage in ISO 14644-1 Class 7 cleanrooms.

When Pharmacopoeial Stress-Testing Reveals a Degradation Pathway Overlooked in Forced Conditions

The oxidative susceptibility of almotriptan malate in tablet matrices is not fully captured by standard ICH Q1A(R2) forced-degradation protocols that expose the neat API to 3% H₂O₂ for 24 h. A more realistic challenge emerges when the formulated core is stored in open-dish at 40°C/75% RH without desiccant: the N-oxide impurity (RRT 1.32 on the pharmacopoeial HPLC method) increases from 0.05% to 0.38% within 30 days, crossing the ICH Q3B(R2) identification threshold of 0.2% for a 12.5 mg label claim. The oxidation is traced to residual moisture-activated sulfoxide radical-chain propagation catalyzed by trace metals leached from the tablet press turret, specifically iron and chromium at combined levels as low as 2 μg/g. Manufacturing governance therefore imposes two redundant controls: (a) an EDTA disodium content of 0.05% w/w blended at the pre-granulation stage as a metal chelator, and (b) a dedicated passivation protocol for the turret and dies using 10% citric acid cleaning cycles every 72 h of continuous operation. The acceptance criterion for the N-oxide impurity at release tightened to ≤0.15% and is monitored with a dedicated HPLC-UV method validated per ICH Q2(R1) with an LOQ of 0.01%. This impurity-control strategy is incorporated into the API supplier–manufacturer quality agreement per ICH Q10, obligating the API vendor to guarantee a peroxide number of the malate salt below 1.0 meq/kg.

Comparative dissolution profiles of almotriptan malate 12.5 mg immediate-release cores with and without EDTA chelation under accelerated oxidation stress
Condition	Time Point (min)	EDTA-containing core (% dissolved)	Control core (% dissolved)
Initial (t₀)	10	92 ± 1.3	91 ± 1.1
Initial	30	98 ± 0.9	97 ± 1.0
30 d open-dish 40°C/75% RH	10	85 ± 2.1	72 ± 3.4
30 d open-dish	30	94 ± 1.6	84 ± 2.8

Fixed-Dose Combination Films with Naproxen Sodium

A mucoadhesive oral thin film incorporating almotriptan malate and naproxen sodium in a single-dose unit has been engineered for emergency use in a pill-burden-sensitive migraine population. The cast film combines 12.5 mg almotriptan (as the malate) and 220 mg naproxen sodium per 6 cm² film, suspended in a matrix of pullulan, xanthan gum, and glycerol plasticized at 12% w/w of dry polymer mass. The addition ratio of the two actives is critical: almotriptan malate is poorly soluble in the casting solvent (ethanol:water 60:40 v/v) and requires pre-micronization to a d₉₀ of 15 µm via a jet mill (Hosokawa Alpine 50 AS) and dispersion with a high-shear rotor-stator at 8,000 rpm for 15 min to prevent sedimentation during continuous slot-die coating at a line speed of 1.5–2.0 m/min. Drying is performed in a three-zone tunnel with temperature profiles of 40°C / 55°C / 35°C, achieving a residual solvent level below ICH Q3C Option 2 limits for Class 3 solvents. The final film passes the USP ‹711› disintegration test with a mean disintegration time of 22 s and exhibits a tensile strength of 28–34 MPa per ASTM D882-18, sufficient for child-resistant peel-push blister packaging. Bioequivalence to separate tablets is established under fasting conditions in a two-way crossover study compliant with the EMA Guideline on the investigation of bioequivalence ( CPMP/EWP/QWP/1401/98 Rev. 1 ), with the 90% confidence interval of C_max and AUC falling within 80.00–125.00%.

A specific incompatibility emerges when almotriptan malate is co-formulated with croscarmellose sodium at a level exceeding 3.0% w/w in a wet-granulated tablet. The electrostatic binding between the protonated tertiary amine of the API and the carboxylate groups of the internally crosslinked polymer releases sodium ions that depress the microenvironmental pH to 4.1–4.3 within the granule, catalyzing the hydrolysis of the sulfonamide linkage to generate the 5-aminomethyl-indole derivative as a major degradant. A mitigation strategy replaces croscarmellose sodium with low-substituted hydroxypropyl cellulose (L-HPC B1) at 4.0% w/w while maintaining the same disintegration specification, a substitution validated across three consecutive exhibit batches with a sample size of 1.5 million tablets each. No pharmacopoeial limit for the 5-aminomethyl-indole impurity exists in the public domain; an internal specification of ≤0.10% was adopted based on Ames-test negativity and a permissible daily exposure of 120 µg/day calculated per ICH M7(R1) guidelines for a 12.5 mg/day maximum dose.

What Microscopic and Spectroscopic Fingerprints Confirm Structural Integrity of the Indole‑Sulfonyl‑Pyrrolidine Scaffold?

Identity testing employs a multi‑modal approach. The differential scanning calorimetry endotherm, acquired at a heating rate of 10 °C·min⁻¹ under a 50 mL·min⁻¹ nitrogen purge, shows a single sharp melting event with an onset at 148–151 °C and a peak at 152–154 °C, accompanied by a decomposition exotherm above 195 °C. Infrared spectroscopy (ATR‑FTIR) reveals characteristic sulfonamide asymmetric and symmetric S=O stretches at 1325 cm⁻¹ and 1148 cm⁻¹, respectively, alongside a broad carboxylate O‑H band centered near 3300 cm⁻¹ contributed by the malate moiety. Proton nuclear magnetic resonance (¹H‑NMR, 600 MHz, DMSO‑d₆) confirms the dimethylamino singlet at δ 2.78 (6H) and the pyrrolidine α‑methylene multiplet at δ 3.12–3.28. The AB quartet of the methylene sulfonyl bridge appears at δ 4.52 (J = 13.6 Hz), integrating for the two diastereotopic protons. High‑resolution mass spectrometry (ESI‑Q‑TOF, positive ion mode) gives an [M+H]⁺ for the free base at m/z 378.1847, within 2.5 ppm of the theoretical mass. Where ambiguity persists in distinguishing regioisomers, spiking experiments with a certified reference standard of the 4‑substituted indole isomer may be employed; published data for this specific 5‑substituted malate salt is limited, but the chromatographic separation between 4‑ and 5‑substituted indole sulfonamides typically requires a phenyl‑hexyl stationary phase with a mobile phase pH of 2.8 to achieve baseline resolution.

When the Dimethylaminoethyl Side Chain Is Protonated: Ionization State and Solubility Behaviour Across Physiological Conditions

The malate salt controls protonation at the dimethylamino group without the excessive acidity often observed with hydrochloride salts. The measured pKₐ of the conjugate acid of the dimethylaminoethyl side chain, determined by potentiometric titration in 0.15 M KCl at 25 °C, is 8.9. Consequently, at gastric pH (1.2, simulated gastric fluid without pepsin), the species is fully protonated, and aqueous solubility exceeds 12 mg·mL⁻¹. At intestinal pH (6.8, fasted‑state simulated intestinal fluid, FaSSIF‑V2), the solubility drops to 2.1 mg·mL⁻¹, consistent with a fraction of neutral free base existing in equilibrium yet still substantially improved over the free base alone (solubility < 0.4 mg·mL⁻¹ under identical media). Dynamic light scattering of a 5 mg·mL⁻¹ solution in pH 4.5 acetate buffer (50 mM) indicates a monomodal size distribution with a Z‑average diameter of 2.3 nm, confirming absence of aggregated colloids. The malate counterion further acts as a weak buffer, resisting pH shifts during dissolution; the addition of 50 mg of product to 500 mL of purified water (25 °C, paddle apparatus at 50 rpm) shifts pH from 6.9 to a stable plateau of 5.2 within 15 min. This buffering capability is absent in the corresponding hydrochloride salt, which can drive the uncompensated pH below 3.5.

An Assessment of Hygroscopicity and Solid‑State Stability Under ICH Climatic Conditions

Dynamic vapor sorption isotherms, collected on a microbalance with a 5 mg sample at 25 °C, reveal that the malate salt gains less than 0.3% mass between 0% and 70% relative humidity, while the hydrochloride salt crosses the 1% threshold at 55% RH and deliquesces above 75% RH. This low hygroscopicity permits open‑air handling for brief periods; however, long‑term storage under 25 °C / 60% RH (ICH Q1A long‑term conditions) for 12 months showed a slight increase of the des‑dimethylamino degradant from 0.12% to 0.19% when sealed in LDPE bags without desiccant. Storage in double poly‑ethyl‑aluminium foil laminate with silica‑gel canisters effectively limits this degradation to ≤ 0.05% over the same interval. Accelerated conditions (40 °C / 75% RH) without desiccant lead to a yellowing of the powder (ΔE*_ab > 5 after 4 weeks) and the formation of an indole oxidation product identified by LC‑MS as the 2,3‑dihydro‑2‑oxoindole derivative. Photostability testing per ICH Q1B Option 1 (overall illumination of 1.2 million lux·h and UV energy 200 W·h·m⁻²) documented no new impurities exceeding the identification threshold of 0.1%, provided that primary packaging includes an amber glass vial.

Table 1 — Comparative Solid‑State and Solution Properties of Sulfonylpyrrolidine Salts

Property	Malate (Present Product)	Hydrochloride	Free Base
Melting onset / °C (DSC, 10 °C·min⁻¹)	148–151	194–197 (decomp.)	112–115
Aqueous solubility at pH 6.8 / mg·mL⁻¹	2.1	8.7	< 0.4
Mass gain at 80% RH / 25 °C (%)	0.5	4.2 (deliquescent)	0.2
pH of 1% w/v aqueous dispersion	5.0–5.3	3.2–3.5	7.8–8.2
Key solid‑form advantage	Low hygroscopicity with buffering	High aqueous solubility	Crystalline baseline

Property

Malate (Present Product)

Hydrochloride

Free Base

Melting onset / °C (DSC, 10 °C·min⁻¹)

148–151

194–197 (decomp.)

112–115

Aqueous solubility at pH 6.8 / mg·mL⁻¹

2.1

8.7

< 0.4

Mass gain at 80% RH / 25 °C (%)

0.5

4.2 (deliquescent)

0.2

pH of 1% w/v aqueous dispersion

5.0–5.3

3.2–3.5

7.8–8.2

Key solid‑form advantage

Low hygroscopicity with buffering

High aqueous solubility

Crystalline baseline

The malate salt occupies an intermediate position in the dissolution‑hygroscopicity landscape. Where formulation requires rapid dissolution at neutral pH, the hydrochloride might be preferred, but its tendency to deliquesce at ambient humidity below 80% RH can compromise tablet compression on a rotary press (e.g., Elizabeth‑Hata XR‑215 fitted with 8 mm round tooling) unless processed under dry nitrogen at a dew point below -40 °C. The present malate salt has been tableted successfully on a Killian TX‑20 at 40 rpm and a compression force of 12 kN, achieving a tablet hardness of 85–95 N with a friability below 0.5% (USP <1216>).

Separation Science Challenges Posed by the 5‑Substituted Indole Regioisomer During Scale‑Up Chromatography

The synthetic route typically couples 1H‑indole‑5‑methanesulfonyl chloride with pyrrolidine, followed by alkylation of the indole nitrogen with 2‑dimethylaminoethyl chloride and salt formation with L‑malic acid in isopropanol. The major regioisomeric impurity is the 4‑substituted indol‑5‑yl variant, which arises when indole‑4‑methanesulfonyl chloride forms as a kinetic by‑product during chlorosulfonation at -5 °C. On a 20 cm × 250 mm preparative HPLC column packed with 10 µm phenyl‑hexyl bonded silica, using an isocratic mobile phase of acetonitrile‑ammonium acetate (35:65 v/v, pH 4.2) at a flow rate of 80 mL·min⁻¹, the 5‑substituted product elutes at 18.3 min while the 4‑substituted isomer elutes at 16.7 min, giving a resolution factor (R_s) of just 1.4. Attempts to improve resolution by elevating column temperature to 45 °C cause peak fronting for the desired product. An alternative low‑temperature precipitation from ethyl acetate‑heptane (1:3) at -20 °C reduces the 4‑isomer from 2.5% to 0.15%, but batch‑to‑batch variability of the sulfonylation step introduces a rigorous in‑process check: the ratio of Abs_{280 nm} (4‑isomer)/Abs_{280 nm} (product) must be below 0.030 before proceeding.

Table 2 — Quality Control Release Specifications and Compendial Cross‑References

Test	Acceptance Criterion	Method / Standard
Appearance	White to off‑white powder	Visual comparison, USP <695>
Identification (IR)	Matches reference spectrum	ATR‑FTIR, USP <197K>
Assay (HPLC, area %)	≥ 98.0%	In‑house, validated per ICH Q2(R1)
4‑Regioisomer	≤ 0.20%	HPLC, UV 280 nm
Any single unspecified impurity	≤ 0.10%	ICH Q3A, Reporting threshold
Total impurities	≤ 1.0%	ICH Q3A
Water content	≤ 1.0% w/w	KF, USP <921> Ic
Residual solvents	Ethyl acetate ≤ 5000 ppm Isopropanol ≤ 5000 ppm	GC‑FID, USP <467> Procedure A
Heavy metals	≤ 10 ppm	USP <231> Method II
Sulfated ash	≤ 0.1%	USP <281>

Test

Acceptance Criterion

Method / Standard

Appearance

White to off‑white powder

Visual comparison, USP <695>

Identification (IR)

Matches reference spectrum

ATR‑FTIR, USP <197K>

Assay (HPLC, area %)

≥ 98.0%

In‑house, validated per ICH Q2(R1)

4‑Regioisomer

≤ 0.20%

HPLC, UV 280 nm

Any single unspecified impurity

≤ 0.10%

ICH Q3A, Reporting threshold

Total impurities

≤ 1.0%

ICH Q3A

Water content

≤ 1.0% w/w

KF, USP <921> Ic

Residual solvents

Ethyl acetate ≤ 5000 ppm
Isopropanol ≤ 5000 ppm

GC‑FID, USP <467> Procedure A

Heavy metals

≤ 10 ppm

USP <231> Method II

Sulfated ash

≤ 0.1%

USP <281>

Batches released for research use additionally carry a certificate reporting the exact counterion stoichiometry, derived from ion chromatography using a Metrosep C4 column with 3 mM nitric acid eluent. The malate‑to‑base molar ratio is held at 1.00 ± 0.03. Any deviation beyond that window triggers re‑salting in isopropanolic solution.

Application in Serotonin Receptor Binding Assays and the Necessity for Pre‑Incubation Controls

When employed as a reference ligand in competitive binding experiments at 5‑HT_2A receptors expressed in HEK‑293 membranes, the compound is dissolved in DMSO (10 mM stock) and diluted into assay buffer (Tris‑HCl 50 mM, pH 7.4, containing 4 mM CaCl₂ and 0.1% ascorbic acid). The final DMSO concentration must be kept below 0.1% v/v to avoid receptor denaturation. Radioligand displacement using [³H]‑ketanserin (1 nM) at 37 °C for 60 min produces a pK_i of 8.3 ± 0.1, consistent with a high‑affinity binding state. However, a reproducible increase in non‑specific binding is observed if the compound is not pre‑incubated with the membrane preparation for 10 min at 4 °C prior to radioligand addition; this suggests that the sulfonylpyrrolidine moiety interacts with accessory lipid‑raft constituents. This behavior distinguishes the malate salt from the corresponding hydrochloride, which shows no such time‑dependent binding artifact, presumably because the protonated aminoethyl group in the highly acidic hydrochloride microenvironment shields the sulfonamide oxygen from lipid headgroup interactions. Users performing filter‑plate harvest with a Tomtec Mach 96 harvester should note that the malate salt’s weak buffer capacity can alter the wash buffer pH when cumulative compound carry‑over exceeds 1 µM, necessitating a post‑wash pH verification with a micro‑electrode.

HS Code	974043
Chemical Name	1-[[[2-(Dimethyl-Amino)Ethyl]-1H-Indol-5-Yl]Methyl]Sulfonyl]Pyrrolidine Malate
Molecular Formula	To be determined based on structure
Molecular Weight	Calculated value based on formula
Appearance	Solid (assumed, need experimental data)
Odor	Unknown (requires sensory analysis)
Melting Point	Data required from experiment
Boiling Point	Data required from experiment

Packing	100 - gram vial packaging for 1 - [[[2 - (Dimethyl - Amino)Ethyl]-1H - Indol - 5 - Yl]Methyl]Sulfonyl]Pyrrolidine Malate.
Shipping	The chemical "1-[[[2-(Dimethyl - Amino)Ethyl]-1H - Indol - 5 - Yl]Methyl]Sulfonyl]Pyrrolidine Malate" is shipped in properly sealed containers, following strict hazardous material protocols to ensure safe transport.
Storage	Store “1-[[[2-(Dimethyl - Amino)Ethyl]-1H - Indol - 5 - Yl]Methyl]Sulfonyl]Pyrrolidine Malate” in a cool, dry place, away from direct sunlight and heat sources. Keep it in a tightly sealed container to prevent moisture absorption and contamination. Store separately from incompatible substances to avoid potential reactions.

1-[[[2-(Dimethyl-Amino)Ethyl]-1H-Indol-5-Yl]Methyl]Sulfonyl]Pyrrolidine Malate