From Piperidine to Pyridine: The “Most Common N-Heterocycle” Shift in FDA Small-Molecule New Drugs (2013–2023) and a Selection Guide (Tables 1–4)

1. Who Is the “Busiest” N-Heterocycle in a Decade of New Drugs?

If we think of small-molecule drugs as combinations of “functional modules,” N-heterocycles are among the most frequently used modules. A striking change from recent decade-level statistics is that the #1 most frequently occurring N-heterocycle has “passed the baton”—from piperidine to pyridine. The conclusions below are based on segmented statistical comparisons of the occurrence frequency/composition of N-heterocycles in U.S. FDA-approved small-molecule drugs.

 

1.1 Two data cards

Table 1. Two time windows and the #1 high-frequency N-heterocycle

 

Time window	Dataset & overall characteristics	#1 most frequent N-heterocycle
1938–2012 (earlier window)	~59% of small-molecule drugs contain at least one N-heterocycle	Piperidine was more common (ranked #1 at the time)
2013–2023 (updated window)	321 newly approved small-molecule drugs; the share containing N-heterocycles rose to 82%	Pyridine rose to #1; piperidine dropped to #2

 

Note: The statistics cover FDA-approved small-molecule drugs (excluding biologics such as antibodies). Different studies may apply slightly different inclusion criteria for “small molecules”; this article follows the definitions used in the original study.

 

1.2 This does not mean “piperidine is no longer important.”

In the last decade of small-molecule design, research teams have invoked pyridine more often as an aromatic module that offers a hydrogen-bond acceptor (HBA) polarity point and clear substitution vectors, helping meet integrated needs such as property fine-tuning + pocket exploration + iterative synthesis. Piperidine remains one of the highest-frequency core modules—it has simply moved from “#1” to “#2.”

2. Five Common “Property Knobs” of the Pyridine Module

Table 2. Five practical “property knobs” for pyridine in medicinal chemistry

 

Knob / module capability	What you “change” structurally	Typical benefits	Common costs/risks	How to verify in practice (examples)
1) A “cleaner” H-bond map	In its unprotonated form, pyridine typically acts as an HBA (and does not donate H-bonds), which can help reduce nonspecific binding and permeability penalties associated with too many HBDs. Upon protonation: HBA is lost → interaction patterns and permeability/efflux may change, so pKa–pH behavior should be verified experimentally.	Preserve key recognition features while reducing the risk of excessive polarity and nonspecific interactions caused by too many donors; often used to balance “binding vs permeability.”	Loss of a donor “anchor” can reduce affinity; in some pockets, missing a donor can destabilize binding modes.	Matched-pair comparison: replace a donor-containing ring with pyridine and compare potency/selectivity; use crystallography/docking or SAR analysis to see whether the H-bond network is reorganized.
2) Fine control of pKa/polarity via substituents	Introduce electron-withdrawing/donating substituents on the ring; change ortho effects and local dipoles.	Pyridine basicity is usually moderate/weak and tunable, enabling fine balancing among solubility, permeability, and target binding (fine-tuning).	Over-tuning pKa may cause problems: salts difficult to form, unfavorable free-base fraction, or permeability/solubility “moving in the wrong direction”; coupled effects with whole-molecule logD, etc.	Measure pKa, logD (or logP), solubility (pH–solubility profile); run parallel permeability/efflux trend assays in cells.
3) Practical substitution “vectors” (2/3/4 positions)	Choose 2/3/4 positions to “project” substituents in different spatial directions; use disubstitution to explore pockets.	Efficient pocket exploration and spatial filling: quickly scan “reach directions” on the same core and build SAR efficiently.	A “good vector” isn’t always better: substitution can introduce torsion/sterics that lead to unfavorable conformations, or place polarity where it shouldn’t be.	Do a positional scan series (2/3/4) plus key physicochemical measurements; use co-crystal/conformational analysis to judge whether the “reach direction” actually hits the intended pocket region.
4) Salt/solid-state tuning (salts/cocrystals are common, but benefits are system-dependent)	Use the pyridine N as a protonatable site; screen acids/counterions for salts, cocrystals, and polymorphs.	More formulation and process options: may improve dissolution, stability, and manufacturability (depending on the scaffold).	Pyridine is relatively weakly basic (pKaH ≈ 5.2), so salt formation drive/stability and solubilization gains depend more on acid choice, pKa matching, overall logD, lattice energy; may bring hygroscopicity/polymorphism, or a “solubility ↑ but permeability ↓” trade-off.	Salt/polymorph screening + dissolution curves; compare free base vs different salts/cocrystals for solubility–permeability–stability/hygroscopicity (and exposure trends in vivo when needed).
5) “Variant expansion”: N-oxide, fused pyridines, bipyridines	Convert pyridine into pyridine N-oxide, fused systems, or bipyridines, etc.	Expand polarity distribution and interaction modes; sometimes yields distinctive property balance or binding modes; a route for “series upgrades.”	Higher polarity may reduce permeability; N-oxides/multi-aza systems may also change metabolic routes and distribution.	Assess metabolic stability and metabolite profiles (N-oxidation/reduction interconversion); measure solubility and permeability/efflux in parallel to confirm whether the “balance is truly better.”

 

Abbreviations

1. HBA = Hydrogen Bond Acceptor: an atom/group that can accept H-bonds (e.g., pyridine nitrogen).

2. HBD = Hydrogen Bond Donor: a group that can donate H-bonds (e.g., –NH, –OH).

3. pKa (negative logarithm of the acid dissociation constant): reflects acid/base strength and ionization tendency at a given pH, directly affecting solubility and permeability.

4. SAR = Structure–Activity Relationship: summarized relationships between structural changes and biological activity changes.

5. N-oxide: a structure type in which the heteroaromatic nitrogen is oxidized to form an N→O unit (e.g., pyridine N-oxide).

 

3. Fifty-Four Pyridine-Containing New Drugs in 10 Years: The Most Common Substitution Patterns and Structural “Engineering” Habits

In an analysis of FDA-approved small-molecule drugs containing pyridine from 2014–2023 (U.S. Food and Drug Administration), a consistent “engineering habit” emerges: 2-substitution is almost the default, disubstitution most often appears as the 2,5-pattern, and more than half of the molecules do not rely on stereocenters to achieve efficacy.

Note: The substitution statistics below come from a compilation of pyridine-containing FDA-approved small-molecule drugs within the 2014–2023 window. They describe “common engineering habits in that decade” and should not be treated as universal rules for the entire pyridine chemical space.

 

3.1 Numeric cards

(a) 54 drugs: From 2014–2023, 54 FDA-approved small-molecule drugs were identified as containing a pyridine ring.

(b) ~90% → 2-position: About 90% have a substituent at the 2-position of pyridine (2-substitution is nearly a “default entry”).

(c) ~55% → disubstituted, often 2,5-: About 55% are disubstituted pyridines, with 2,5-disubstitution most common.

(d) ~33% oncology is the largest single category (but not “most”): Oncology accounts for 18/54 ≈ 33%, the largest single category, while the rest are broadly distributed across CNS (Central Nervous System), infection, rare diseases, and more.

(e) The literature also notes >50% of molecules are achiral (no stereocenters).

 

3.2 Notes: Why is the 2-position so “hot”?

1. Structurally, 2-substitution often provides a more favorable “reach direction” and/or conformational constraint, helping substituents enter binding pockets more consistently.

2. Practically, 2-halo/activated substrates are common and SNAr/cross-coupling routes are mature—making the “2-position default entry” a highly iterable real-world strategy.

3. From synthesis and functional-group interconversion perspectives, the 2-position is often more efficient and scalable for exploration—so it tends to win both on “can we make it?” and “can it reach the pocket?” ends.

 

3.3 What does “>50% achiral” mean?

1. “More than half achiral” does not mean “chirality is unimportant.” It only indicates that, within this set of pyridine-containing new drugs, many projects did not require stereocenters for key efficacy/selectivity. Once chirality is introduced (especially in polyheterocycle or spiro systems), it can still strongly affect conformation, selectivity, and in vivo exposure.

 

4. Representative Drugs by Therapeutic Area: Understanding “What Pyridine Does Here”

 

Table 3. Representative pyridine-related drugs across disease areas

 

Area	Representative drug	First FDA approval (U.S.)	Main indication	Main target/mechanism	What role does pyridine play here?
Oncology	Sotorasib / Lumakras	2021-05-28	Non-small cell lung cancer (NSCLC) with KRAS G12C mutation: locally advanced or metastatic NSCLC previously treated with ≥1 systemic therapy	Covalent inhibition of KRAS G12C (KRAS = Kirsten rat sarcoma viral oncogene homolog; G12C = glycine→cysteine substitution at codon 12); RAS GTPase family inhibitor	As an N-heteroaromatic fragment, provides an “acceptor-type polarity point” (HBA) and a tunable site for physicochemical fine-adjustment, supporting overall balance between binding and exposure (a common design usage rather than a single-mechanism attribution).
Immunology / Rare disease	Leniolisib / Joenja	2023-03-24	Activated PI3Kδ syndrome (APDS) in adults and pediatric patients ≥12 years	PI3Kδ inhibition (PI3Kδ = phosphoinositide 3-kinase delta)	As an engineerable N-heteroaromatic module, provides predictable HBA polarity and “substitution vectors” for pocket fit and property tuning in polyheterocyclic scaffolds.
Migraine	Gepant family (CGRP receptor antagonists): Ubrogepant/Ubrelvy (2019-12-23), Rimegepant/Nurtec ODT (2020-02-27), Atogepant/Qulipta (2021-09-28)	2019-12-23; 2020-02-27; 2021-09-28	Ubrogepant & Rimegepant: acute treatment of migraine with or without aura; Atogepant: prevention of episodic migraine	CGRP (calcitonin gene-related peptide) receptor antagonism (small-molecule CGRP receptor antagonists)	In highly substituted, multi-heterocycle molecules, pyridine often serves as a directionally defined polar module (HBA) and a replaceable tuning site to achieve a workable window in ADME trade-offs (absorption, distribution, metabolism, excretion).
Infection	Delafloxacin / Baxdela	2017-06-19	Acute bacterial skin and skin structure infections (ABSSSI)	Fluoroquinolone antibacterial: inhibition of bacterial DNA gyrase and topoisomerase IV (typical quinolone mechanism)	The structure clearly contains a “6-amino-3,5-difluoropyridin-2-yl” fragment (a pyridine-containing substituent); this pyridine fragment contributes to overall electronic/polarity settings and provides synthetically iterable substitution sites.
Parkinson’s disease	Opicapone / Ongentys	2020-04-24	Adjunct to levodopa/carbidopa for end-of-dose “wearing-off/OFF” fluctuations in Parkinson’s disease	COMT inhibition (COMT = catechol-O-methyltransferase)	Contains a pyridine N-oxide variant: a pyridine-1-oxide unit, illustrating how “the pyridine family” can be finely tuned via N-oxidation and other variants in polarity, solid-state properties, and metabolic features (effects depend on whole-molecule design).
Diagnostic imaging	Piflufolastat F 18 / Pylarify	2021-05-26	PSMA (prostate-specific membrane antigen) PET imaging for prostate cancer–related PSMA-targeted diagnosis	Radiodiagnostic (PET): PSMA-targeting ligand–mediated molecular imaging	An ¹⁸F (fluorine-18)-labeled fluoropyridine fragment is used for radionuclide incorporation on the imaging side and for physicochemical property adjustment.

 

5. Reminder: Pyridine Is a Knob—And It Requires Trade-offs

 

Table 4. Key trade-offs and early verification recommendations

 

Trade-off point	Why it happens	Possible consequences	What to verify early (recommended)
1) Metabolic N-oxidation and pathway reshaping	N-heteroaromatics (including pyridines) can be oxidized under certain substitution patterns to N-oxides and related metabolites; impact depends on substitution, pKa, and overall electronic environment	Lower exposure, altered clearance routes, changed metabolite profile (may affect safety/interaction assessment)	Microsomal/hepatocyte metabolic stability; metabolite ID (whether N-oxide appears and whether proportions vary by species)
2) Solubility vs permeability tension	Pyridine often introduces acceptor-type polarity (HBA) and shifts pKa; higher polarity may improve solubility but reduce membrane permeability; outcomes are jointly controlled by pKa, logD, and intramolecular H-bonding (IMHB)	Solubility improves but permeability worsens (or vice versa), leading to exposure/efficacy deviating from expectations	pKa, logD; solubility (multiple pH points); permeability models (e.g., PAMPA/Caco-2) and efflux trend comparisons
3) CYP inhibition/coordination → DDI risk (structure-dependent, not inevitable)	Some aromatic nitrogens can coordinate to CYP heme iron or inhibit via other mechanisms; strength depends on nitrogen accessibility, electronic environment/basicity, and overall hydrophobic–polar balance—having a pyridine does not automatically mean strong inhibition	CYP inhibition or time-dependent inhibition (TDI), raising DDI (drug–drug interaction) risk	CYP inhibition panel (IC₅₀); TDI assessment; if needed, reactive metabolite/mechanism-based inhibition checks
4) “Variants are not forbidden”: N-oxides can be part of an API	N-oxide and related variants are not inherently unusable; with the right overall design and exposure/metabolism balance, they can be part of an API (active pharmaceutical ingredient)	May achieve distinctive polarity and solid-state/exposure balance; may also introduce new permeability/metabolism challenges (depends on whole molecule)	Evaluate the solubility–permeability–metabolic stability “triad”; when needed, compare N-oxide vs the parent pyridine in parallel datasets

 

6. Will Pyridine’s Lead Likely Continue Over the Next Decade?

6.1 “Pyridine taking the top spot” is not an accident

a) In a systematic analysis of 321 FDA-approved small-molecule new drugs from 2013–2023, the share of compounds containing at least one N-heterocycle rose to 82%, and pyridine replaced piperidine as the most frequently occurring N-heterocycle. Meanwhile, the number of fused N-heterocycles increased and has been linked to the rising structural complexity of recent oncology new drugs.

 

6.2 Three trends that may plausibly persist

a) Trend 1: N-heterocycles will likely remain a “main language” in small-molecule design—because they simultaneously provide controllable polarity, controllable substitution vectors, and synthetically accessible variant space.

b) Trend 2: Structural complexity may continue to move upward—especially in areas such as oncology, where fused polyheterocycles and heavily substituted scaffolds keep increasing.

c) Trend 3: Pyridine will probably remain common, but may not stay #1 forever—because as screening strategies, synthetic methods (data-driven / automated route design), and drug modalities (oral small molecules, radiodiagnostics, targeted delivery, etc.) continue to evolve, the “most favored ring system” could shift again.

 

6.3 The key inflection: what will future “selection pressure” favor?

a) Will the field continue to prefer pyridine systems that are aromatic, have clear substitution vectors, and allow fine-tunable polarity, while further “upgrading the pyridine family” via ring fusion, increased aza density, and sp³-ification?

b) Or, as target classes and delivery modalities change, will a “next-generation high-frequency heterocycle” better matched to new needs emerge and push pyridine out of the #1 position?

c) The answer for the next decade may not be a simple “pyridine vs. one new ring.” More likely, advantageous ring systems will diverge by disease area and modality—and coexist long-term.

 

7. Product Selection Guide and Representative Product Tables for Pyridine / N-Heterocycles (Tables 1–4)

​Selection guide table

Typical need / scenario	Which table to check first	Why this table fits best	What you will find in the table (representative items)
Need reference standards for LC–MS quantitation, impurity profiling, stability, or metabolism studies of new drugs / radiodiagnostics	Table 1 | Representative drug / diagnostic reference standards (Moligand™ / radiolabeled references)	Concentrates reference materials for pyridine / poly-aza new drugs and PET diagnostic references from the last decade	Sotorasib, leniolisib, gepant-family references, opicapone, anti-infective references, lenacapavir, flortaucipir (18F), Dcfpyl F-18, etc.
Choosing a core scaffold / fragment set / “property knobs”: comparing “pyridine itself vs hydroxy/amino/carboxylate/bipyridine/N-oxide” effects on pKa, polarity, H-bond map, salt form, and conformation	Table 2 | Pyridine cores and derivative/benchmark scaffolds	Core- and variant-centered table—best for structure–property benchmarking and selecting starting scaffolds (a modular medicinal-chemistry style)	Pyridine; 2/3/4-methylpyridines; 2/3/4-aminopyridines; 2/4-hydroxypyridines; nicotinic acid / isonicotinic acid / picolinic acid; bipyridines; pyridine N-oxides, etc.
You have decided to use a pyridine ring and now want SAR expansion / vector exploration: how to “reach” from positions 2/3/4, and which starting materials are fastest (halides, boronic acids, borylation reagents)	Table 3 | Pyridine building blocks for library expansion (halides / boronic acids / borylation)	A collection of synthetic “entry points”: halides and boronic acids map to the most common cross-coupling and SNAr routes, ideal for parallel expansion and rapid construction of substituted pyridines	2-chloro/2-fluoro/2-bromo/3-bromo/4-bromopyridine and salts; pyridine-2/3/4-boronic acids; bis(pinacolato)diboron, etc.
Route building, scale-up, or parallel reactions: need solvents, bases, catalysts, coupling reagents, oxidants, and controls for “pyridine N-oxidation / reactivity risk”	Table 4 | General synthetic & evaluation support set (solvents/bases/catalysis/coupling/oxidation/trapping)	One table for “running the chemistry” and “screening risks”: covers both reaction systems and early risk checks (GSH/NAC trapping) plus methodology (LC–MS solvents)	MeCN (with formic acid), THF, DMF, DMSO; K₂CO₃/Cs₂CO₃/DBU/DIPEA; Pd(OAc)₂/Pd(PPh₃)₄/CuI; EDC/CDI/HATU/DMAP; Oxone/mCPBA/H₂O₂; GSH/NAC, etc.
First time doing “pyridine-related selection” and want the fastest route with minimal information: buy reference standards? buy building blocks? buy supporting reagents?	Check this navigation row first, then jump to the corresponding sub-table by your need	Triage by “the problem you’re solving”: references (validation/methods) → Table 1; scaffolds/property knobs → Table 2; library entry points → Table 3; reaction & risk support → Table 4	Quickly locate the table you need

 

Table 1 | Representative Drug / Diagnostic Reference Standards (Moligand™ / Radiolabeled References)

 

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features & selection use (for N-heterocycles / pyridine systems)
Drug reference | Oncology (representative N-heterocycle drug)	2296729-00-3	S414206	Sotorasib (AMG510)	Moligand™, ≥98%	New-drug reference standard for analytical methods and impurity/stability/metabolism studies; a representative N-heterocycle drug case, useful for discussion/benchmarking of “pyridine / N-heteroaromatic modules.”
Drug reference | Oncology (alternative reference form)	2252403-56-6	S414293	Sotorasib (AMG510) racemate	Moligand™, ≥97%	Reference source representing different stereochemical/form-related states of the same drug; useful for chiral/conformation-related methods and quality studies (common needs for N-heterocycle drug systems).
Drug reference | Immunology / Rare disease (representative N-heterocycle drug)	1354690-24-6	L414153	Leniolisib (CDZ 173)	Moligand™, ≥99%	New-drug reference for PI3Kδ-related method development and impurity/metabolism/pharmacology studies; representative of “compact polyheterocyclic scaffolds.”
Drug reference | Migraine (representative N-heterocycle drug)	1374248-81-3	A607801	Atogepant	Moligand™, ≥98%	New-drug reference for CGRP-pathway methods and impurity/stability studies; useful as a case benchmark for “polarity-point placement in multi-heterocycle systems.”
Drug reference | Migraine (representative N-heterocycle drug)	1289023-67-1	B125641	BMS-927711, CGRP receptor antagonist	Moligand™, ≥98%	Representative CGRP receptor antagonist reference; for method development and structure–property benchmarking (polarity and vector arrangement in N-heterocycle scaffolds).
Drug reference | Migraine (representative N-heterocycle drug)	1374248-77-7	U614612	Ubrogepant	Moligand™	CGRP receptor antagonist reference; supports method development and case discussions of “ADME trade-offs in multi-heterocycle systems.”
Drug reference | Parkinson’s (N-oxide variant representative)	923287-50-7	O356703	Opicapone	Moligand™, ≥98%	Representative case of a pyridine N-oxide variant; suitable for discussions and QC studies on “controllable variants vs manageable trade-offs.”
Drug reference | Infection (pyridine-substituent representative)	189279-58-1	D125392	Delafloxacin	Moligand™, ≥98%	Fluoroquinolone antibacterial reference; contains a pyridine substituent—useful as a case for “pyridine modules within mature antibacterial chemical space.”
Drug reference | Infection	245765-41-7	O303182	Ozenoxacin	Moligand™, ≥98%	Anti-infective reference for antibacterial methods and impurity control; supports examples within N-heteroaromatic drug lineages.
Drug reference | Infection (prodrug)	856867-55-5	T413160	Tedizolid phosphate	≥98%	Anti-infective prodrug reference for analytical methods and impurity control; also supports case examples of N-heterocycles in infectious-disease therapeutics.
Drug reference | Hematology (representative N-heterocycle drug)	1446321-46-5	V414047	Voxelotor	Moligand™, ≥98%	Representative small-molecule reference for method development and impurity/stability studies; expands examples of N-heterocycles beyond oncology.
Drug reference | Rare disease / Antiviral (representative N-heterocycle drug)	193275-84-2	L125407	Lonafarnib	Moligand™, ≥95%	Reference for complex scaffolds; supports method development and impurity/metabolism studies and case explanations of “complex N-heterocycle systems.”
Drug reference | Antiviral (representative N-heterocycle drug)	2189684-44-2	L611483	Lenacapavir	Moligand™	Antiviral representative reference for analytical methods, impurities, and stability of complex scaffolds (polyheterocycle / highly substituted features).
Radiodiagnostic reference | Tau PET	1522051-90-6	F610343	Flortaucipir (18F)	Moligand™	Radiodiagnostic reference for PET methods/QC discussions, highlighting the use of N-heterocycle scaffolds on the diagnostic side.
Radiodiagnostic reference | PSMA PET	1207181-29-0	D671218	Dcfpyl F-18	——	PSMA PET radiodiagnostic reference (DCFPyL type); for radiochemistry/QC method discussions, highlighting the “N-heteroaromatic scaffold + radiolabeling” application scenario.
Drug reference / Pyridine scaffold | Neurology	54-96-6	D154393	3,4-Diaminopyridine	Moligand™, ≥98%	Benchmark diaminopyridine scaffold reference; used in ion-channel related research and as a structural comparator for “adding multiple donors/polarity on pyridine.”

 

Table 2 | Pyridine Cores and “Derivative / Benchmark Scaffolds” (Hydroxy/Amino/Methyl/Carboxylic Acid/Bipyridine/N-oxide)

 

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features & selection use (for N-heterocycles / pyridine systems)
Pyridine core | Basic fragment	110-86-1	P111513	Pyridine	Anhydrous, ≥99.8%	Fundamental N-heteroaromatic core; used for salt formation/coordination/derivatization benchmarks and also commonly used as a solvent/basic additive in N-heterocycle chemistry.
Pyridine base additive / hindered base	108-48-5	L431380	2,6-Dimethylpyridine	Distilled, ≥99%	Hindered pyridine base (lutidine); commonly used as a mild acid scavenger/base additive to control selectivity and suppress side reactions in N-heterocycle systems.
Pyridine building block | Methyl substituted (GC standard)	109-06-8	M108695	2-Methylpyridine	Standard for GC, ≥99.5% (GC)	2-Methylpyridine (2-picoline) for positional isomer/basicity/polarity benchmarking; also used as a GC/method and impurity reference.
Pyridine building block | Methyl substituted (positional isomer)	108-99-6	P109210	3-Methylpyridine	≥99.5% (GC)	3-Methylpyridine (3-picoline) for “substitution position → property/conformation” comparisons; suitable as a GC/impurity standard or structural benchmark.
Pyridine building block | Methyl substituted (positional isomer)	108-89-4	P105226	4-Methylpyridine	≥98%	4-Methylpyridine (4-picoline) for positional isomer benchmarking and fine property tuning; also a starting point for derivatization.
Pyridine building block | Amino substituted	504-29-0	A105221	2-Aminopyridine (2-AP)	CP grade	A widely used “polarity + vector” building block; suitable for SNAr, amidation, and fused-heterocycle derivatization.
Pyridine building block | Amino substituted	462-08-8	A107135	3-Aminopyridine	Analytical standard	Aminopyridine building block with a 3-position vector; used for SAR vector exploration and derivatization to amides/ureas/sulfonamides, etc.
Pyridine building block | Amino substituted	504-24-5	A113920	4-Aminopyridine	≥98%	Commonly used for SNAr, amidation, and salt-form benchmarking; also a representative classic scaffold fragment in neuro-related chemistry.
Hydroxypyridine / tautomerism benchmark	142-08-5	H108693	2-Hydroxypyridine	≥97%	Classic benchmark tied to 2-pyridone tautomerism; used to study H-bond maps/polarity and conformational effects.
Hydroxypyridine / tautomerism benchmark	626-64-2	H482399	4-Hydroxypyridine	Reagent grade	Representative hydroxylated pyridine fragment for HBA/HBD (tautomerism) comparison, polarity/H-bond profiling, and heterocycle derivatization.
Pyridine variant | N-oxide	694-59-7	P165276	Pyridine N-oxide	≥98%	Benchmark N-oxide variant for metabolism/polarity comparisons; also used as a synthetic intermediate.
Pyridine carboxylic acid | Vitamin B3 / salt-form handle	59-67-6	N433035	Nicotinic acid	PharmPure™, USP	Pyridine-3-carboxylic acid; used for derivatization (amides/esters) and salt/solubility benchmarking.
Pyridine derivative | Vitamin B3 / polarity benchmark	98-92-0	N108087	Nicotinamide	For cell culture (incl. insect), ≥99.5% (HPLC)	Classic “pyridine carboxamide” scaffold (vitamin B3 family); used as an amide-fragment benchmark and as a nutrient additive in cell-based systems.
Pyridine carboxylic acid | positional isomer benchmark	55-22-1	I101094	Isonicotinic acid (IN)	AR, Moligand™, ≥99%	Pyridine-4-carboxylic acid; commonly used for “vector/salt-form/amidation” comparisons and positional isomer studies.
Pyridine carboxylic acid | 2-position “vector + polarity”	98-98-6	P101920	Picolinic acid	≥99%	Pyridine-2-carboxylic acid; used for amidation/salt/coordination benchmarking, often in “2-substitution/ortho effect” discussions.
Bipyridine / coordination scaffold	366-18-7	D108977	2,2′-Bipyridine	AR, ≥99%	Classic bidentate ligand/scaffold fragment; used in coordination/catalysis and as a structural benchmark for bipyridine motifs.
Bipyridine / coordination scaffold	553-26-4	B105218	4,4′-Bipyridine	Analytical standard, anhydrous	Common bipyridine scaffold used in coordination chemistry/materials and fragment chemistry; also a benchmark for “di-pyridine” systems.
Bipyridine derivative | steric/conformation benchmark	1762-34-1	D154986	5,5′-Dimethyl-2,2′-bipyridine	≥98%	Sterically hindered bipyridine scaffold for coordination/catalysis and benchmarking “steric change → conformation/electronic effects.”

 

Table 3 | Pyridine “Library-Expansion Building Blocks” (Halides / Boronic Acids / Borylation)

 

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features & selection use (for N-heterocycles / pyridine systems)
Halopyridine | SNAr / coupling entry	109-09-1	C474470	2-Chloropyridine	99%	High-frequency “vector entry” at the 2-position; used for SNAr with N/O/S nucleophiles or cross-coupling to build 2-substituted pyridines.
Fluoropyridine | SNAr entry	372-48-5	F120342	2-Fluoropyridine	≥99%	Common SNAr substrate enabling rapid introduction of amines/heterocycles; aligns with the synthetic accessibility behind the high frequency of 2-substitution.
Halopyridine | coupling entry	109-04-6	B109679	2-Bromopyridine	≥98%	Used in Suzuki/Negishi and related couplings to build 2-substituted pyridines; a core building block for “2-vector exploration.”
Halopyridine | coupling entry	626-55-1	B106977	3-Bromopyridine	≥98%	For building 3-substituted pyridine derivatives; supports SAR vector exploration and pocket-filling.
Halopyridine | coupling entry	1120-87-2	B302216	4-Bromopyridine	≥97%	Free-base form for cross-coupling to build 4-substituted pyridines (clear vector, efficient expansion).
Halopyridine | more stable salt form	19524-06-2	B102732	4-Bromopyridine hydrochloride	≥98%	Stable salt supply form for 4-bromopyridine; suitable as a standardized starting material for scale-up/parallel synthesis.
Halopyridine | more stable salt form	74129-11-6	B152112	4-Bromopyridine hydrobromide	≥98%	Salt form for easier storage and weighing; used in cross-coupling to build 4-substituted pyridines and improve reproducibility.
Pyridine boronic acid | Suzuki building block	197958-29-5	P123314	Pyridine-2-boronic acid (contains variable amounts of anhydride)	≥95%	Rapid access to 2-substituted pyridine derivatives via Suzuki coupling; matches the high-frequency 2-substitution pattern and suits parallel synthesis.
Pyridine boronic acid | Suzuki building block	1692-25-7	P396303	Pyridine-3-boronic acid (contains variable amounts of anhydride)	≥98%	Enables rapid introduction of a “pyridin-3-yl” fragment via Suzuki; supports parallel expansion and SAR vector exploration.
Pyridine boronic acid | Suzuki building block	1692-15-5	P113743	Pyridine-4-boronic acid (contains variable amounts of anhydride)	≥96%	For Suzuki introduction of a “pyridin-4-yl” unit; commonly used when a linear vector N-heteroaromatic fragment is desired.
Borylation reagent | upstream building block	73183-34-3	B396365	Bis(pinacolato)diboron	≥99%	B₂pin₂ commonly used for borylation followed by Suzuki coupling; supports rapid construction of diverse substituted pyridines/bipyridines and fused N-heterocycles.

 

Table 4 | General “Support Set” for Synthesis & Evaluation (Solvents / Bases / Catalysis / Coupling Reagents / Oxidation / Trapping)

 

Category	CAS No.	Aladdin Cat. No.	Name	Spec / Purity	Product features & selection use (for N-heterocycles / pyridine systems)
Analytical/LC–MS solvent & mobile-phase additive	75-05-8	A433526	Acetonitrile solution	MS grade (MS), UltraPureChrom™, UHPLC grade, contains 0.1% (v/v) formic acid	A standard organic phase for LC–MS/UPLC; suitable for quantitative methods and impurity analysis of N-heterocycles/pyridines; 0.1% formic acid promotes protonation and improves peak shape.
Anhydrous solvent | general for heterocycle synthesis/coupling	109-99-9	T431417	Tetrahydrofuran (THF)	For DNA & peptide synthesis (max 0.005% H₂O)	Anhydrous THF is widely used in metalation/coupling/reduction systems involving N-heterocycles and in peptide/nucleic-acid workflows; low water helps reproducibility in halopyridine/boronic-acid couplings.
Solvent | drug dissolution/screening	67-68-5	D103280	Dimethyl sulfoxide (DMSO)	Pharmaceutical grade, PharmPure™	A common solvent for N-heterocycle APIs/fragments; suitable for dissolving pyridine-containing APIs/references for bioassays and solubility/stability controls.
Anhydrous solvent | polar aprotic	68-12-2	D119450	N,N-Dimethylformamide (DMF)	Anhydrous, ≥99.8%	Common solvent for halopyridine SNAr and amidation/activation systems; dissolves polar N-heterocycles well, supporting scale-up and parallel reactions.
Inorganic base | common for SNAr/coupling	584-08-7	P485463	Potassium carbonate	Anhydrous, high purity, reagent grade, ≥99%	Mild inorganic base frequently used for halopyridine SNAr, N-alkylation, and various cross-couplings; supports building 2/3/4-substituted pyridines.
Inorganic base | strong carbonate	534-17-8	C432848	Cesium carbonate	purum p.a., ≥98% (T)	Often used to boost conversions for challenging halopyridines in coupling/SNAr and N-alkylation; broadens substrate scope and improves yields.
Metal salt/catalyst additive | coupling systems	7681-65-4	C433811	Copper(I) iodide	Anhydrous, ≥99.995% metals basis	Common additive in Sonogashira/Ullmann-type systems; used to build C–N/C–C bonds involving N-heteroaromatics (including pyridines).
Cross-coupling catalyst precursor	3375-31-3	P432639	Palladium(II) acetate (47% Pd)	For synthesis	Common Pd(II) precursor used in Suzuki/Buchwald-type couplings to construct substituted pyridines, bipyridines, and fused N-heterocycles.
Cross-coupling catalyst | Pd(0)	14221-01-3	T111021	Tetrakis(triphenylphosphine)palladium(0)	Pd ≥8.9%	A classic catalyst for Suzuki and related couplings; enables rapid construction of substituted pyridines, pyridine–aryl links, and bipyridine derivatives.
Organic base/acid scavenger | peptide/bond-forming systems	7087-68-5	N433364	N-Ethyl diisopropylamine solution	For peptide synthesis, ~2 M in 1-methyl-2-pyrrolidinone	DIPEA is widely used as a base in amidation/coupling; especially common when forming amide bonds from nicotinic/isonicotinic/pyridine-carboxylic acids—well suited for parallel synthesis.
Strong organic base | general acid scavenger/ring closure	6674-22-2	D106478	DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene)	≥99%	A non-nucleophilic strong base; used for N-heterocycle derivatization, cyclizations/eliminations, and bond-forming steps—helpful in optimizing difficult transformations.
Bond-forming reagent | carboxyl coupling	25952-53-8	A638729	Aladdin™ EDC	Analytical standard	EDC enables carboxylic acid–amine coupling to form amides; suitable for rapid derivatization of nicotinic/isonicotinic/pyridine-carboxylic acids.
Bond-forming reagent | carbonyl activation	530-62-1	C109315	CDI (N,N′-Carbonyldiimidazole)	≥99%	CDI activates acids/alcohols via acyl imidazole intermediates; useful for forming amides/ureas/carbonates from pyridine carboxylic acids and related substrates.
Bond-forming reagent | high-efficiency amidation	148893-10-1	H109327	HATU	≥99%	A high-efficiency coupling reagent; well suited for hindered or low-reactivity pyridine-carboxylic acid substrates in medicinal-chemistry parallel synthesis.
Pyridine-derived catalyst | acylation promotion	1122-58-3	D109207	DMAP (4-Dimethylaminopyridine)	≥99%	Classic acylation/esterification catalyst; improves coupling efficiency and yield for derivatization of pyridine acids, phenols, and related substrates.
Oxidant | mild oxidation/clean-up	7722-84-1	H755825	Hydrogen peroxide solution	For microbiology, 3%	Used for mild oxidation and system clean-up; can serve as an oxidative-condition control in pyridine systems (evaluate substrate stability case-by-case).
Oxidant | common for N-oxidation/heterocycle oxidation	70693-62-8	P485766	Potassium peroxymonosulfate	For synthesis	Oxone is commonly used for oxidation of heterocycles and N-hetero systems (including N-oxidation pathway exploration); can also act as a chemical “simulation control” for potential metabolic N-oxidation (conditions may require optimization).
Oxidant | N-oxidation/peracid oxidation	937-14-4	C106492	mCPBA (3-Chloroperbenzoic acid)	≥85%	Widely used for pyridine N-oxidation and other functional-group oxidations; suitable for preparing N-oxide variants and oxidative-condition controls.
Bio/safety screening | endogenous thiol	70-18-8	G105427	Glutathione (reduced) (GSH)	Moligand™, for cell culture, ≥98%	Common trapping agent for reactive metabolites/electrophiles; used in early risk screening for N-heterocycle programs and as an antioxidant control in cell systems.
Bio/safety screening | thiol trapping	616-91-1	A105421	N-Acetyl-L-cysteine (NAC)	PharmPure™, USP, Ph.Eur, ≥98.5%	A common thiol trap and antioxidant control; used to assess potential reactive intermediates/electrophile risk in N-heteroaromatic programs when trapping assays are needed.

 

Note: The above are representative Aladdin products. For additional specifications, please refer to the full product list at the end of the article or search by product name/CAS on the Aladdin website.

 

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