Piperidine and Its Derivatives: Controllable Design of Charge, Conformation, and Connecting Exit with Product Navigation (Tables 1–5)

1.Where Do You Encounter "Piperidine"? Why Is It Often Used as a Reusable Tool?

If you're working on molecular optimization, processes, or material formulations, "piperidine" is likely not seen as a "single chemical" but rather as a "reusable structural/functional motif":

1. In Drugs/Lead Structures: The piperidine ring is often used for fragment replacement and property fine-tuning—providing a clear nitrogen center (capable of salting and charge modulation) and offering a relatively stable three-dimensional occupation.

2. In Synthesis and Methodology: It often appears as a base/nucleophilic reagent/process additive; for example, in Fmoc solid-phase peptide synthesis, 20% piperidine/DMF is one of the classic deprotection systems.

3. In Materials Chemistry: You will repeatedly encounter "(tetramethyl)piperidine" derivatives in the HALS (Hindered Amine Light Stabilizers) family; their stabilization mechanism is closely related to the renewable amine/nitroxyl free radical cycle.

Behind these scenarios, there is a common R&D pain point:

1. Poor solubility/salt formation/formulation instability (leading to poor reproducibility, narrow process windows)

2. Molecule shape is too "soft" (high flexibility, making structure-activity relationships hard to converge)

3. Need for a "controllable connection point" (a site that can be derivatized, used as a reference, without pushing overall properties to extremes)

The reason piperidine is frequently used is because it can often address both of these points in a more "engineerable" way:

1. Charge state is designable (clear protonation/salt formation pathways that help bring aqueous phase behavior under control)

2. Three-dimensional occupation is more stable (the conformation of the saturated six-membered ring offers a cleaner comparison, aiding system scanning)

2.Basic Concept Introduction

2.1 What is Piperidine?

1. Definition (Parent Core): Piperidine is a six-membered saturated nitrogen-containing heterocycle, often understood as "a carbon in cyclohexane replaced by nitrogen."

2. Identity Information: Molecular formula: C₅H₁₁N, CAS 110-89-4.

3. Common Physical-Chemical Information: Boiling point at standard pressure is around 106.2 °C.

4. Acidity/Basicity: The conjugate acid of piperidine, pKaH ≈ 11.2, is typically protonated in aqueous phase (pH ≈ 7). This makes salt formation/solubility easier to adjust in formulations, but permeability/excretion and clearance metrics need to be considered—higher solubility does not necessarily lead to increased exposure.

2.2 What Does "Piperidine and Its Derivatives" Typically Refer to?

"Piperidines" generally refers to "a large class of compounds with a piperidine ring in their structure." To quickly determine what property differences they might bring, it’s effective to first look at the following three key variation points:

1. First Look at the Nitrogen (Determining Charge/Salt Type/Reactivity): N–H (piperidine parent core) vs N-alkylation (tertiary amines) vs quaternization (permanent positive charge)

2. Then Look at Substitution Positions and Stereochemical Information (Determining Shape and Interactions): Substitution at positions 2/3/4, cis/trans, or chiral centers changes the conformation distribution and binding mode.

3. Finally, See If It Is Further "Hardened" (Stronger Conformational Restrictions): Bicyclic/bridged/ring-fused structures significantly alter the three-dimensional shape and accessibility.

These variations systematically affect: basicity and salt behavior, solubility/distribution, permeability and distribution, metabolic stability, and binding modes—so even though they are all classified as piperidine derivatives, their differences are often not minor adjustments but can lead to significant property and performance changes.

2.3 Common Confused Terms

Name	Key Difference	Common Misunderstanding
Piperidine	A six-membered saturated ring with nitrogen (parent core)	Confused with "Piperazine"
Piperazine	A six-membered ring with two nitrogens at positions 1,4	Not the same parent core; significant differences in acidity/polarity
Piperidinium Salt	Salt formed by protonation of piperidine (or its tertiary amine derivative); charge state is pH-reversible	Misinterpreted as a "permanent positive" quaternary ammonium salt
Quaternary Ammonium Piperidinium	N-alkylation leading to R₄N⁺, permanent positive charge, no N–H	Mistaken for "salt formation," leading to misjudging solubility/permeability

3.Structural Features

In the previous section, we discussed the types of nitrogen, substitution positions, stereochemical information, and the possibility of restricted conformation. The ultimate decisions boil down to three main points: A) charge state, B) three-dimensional directionality, and C) connection exit.

3.1 A: Charge State and Salt Type (Reversible Protonation vs. Permanent Positive Charge)

1. Free Base (B) ↔ Piperidinium Salt (BH⁺): This is determined by system pH and the conjugate acid pKaH. The common pKaH for piperidine is around 11.2, so it usually prefers the protonated form in neutral aqueous phase. This is one reason why piperidine is often used for "salting, pH-controlled aqueous phase behavior."

2. Quaternary Ammonium Piperidinium (R₄N⁺): This form is permanently positively charged, unaffected by pH. It acts more like a "fixed ionic fragment," commonly seen in ionic liquids, electrolytes, and phase transfer systems.

Quick Decisions:

1. If adjustable salt formation/solubility/distribution is needed (with an aim to modulate aqueous phase behavior via acid addition salts, pH, or salt type): piperidine or its piperidinium salts are preferred.

2. If permanent ionic characteristics are needed (no pH-dependent charge changes): Only then should you consider quaternary ammonium piperidinium.

Note: N-substitution can alter basicity and salt formation behavior. "Having the same piperidine ring" doesn't mean the pKaH will necessarily be the same—always go back to the specific structure for judgment.

3.2 B: Three-Dimensional Shape and Conformation (Chair Conformation Provides More Predictable Occupation)

Piperidine is a six-membered saturated ring, usually adopting a chair conformation. The axial/equatorial positioning of substituents will directly affect how the substituent "extends out." Therefore:

1. Substitution at positions 2/3/4, or changing cis/trans, R/S configurations, often leads to significantly different spatial directionality and interaction modes.

2. Especially substitution at position 2, which may be influenced by stereoeffects and change axial/equatorial preferences, thus affecting overall conformation distribution.

This is why piperidine is often considered "easier to converge" in structure-activity comparisons: you can use a relatively limited set of conformations and attribute differences more clearly to substitution positions and stereochemistry.

Important Note: Non-bicyclic piperidine still undergoes chair flipping. Its predictability primarily comes from how substituents affect axial/equatorial orientation, not from the complete rigidity of the ring itself.

3.3 C: Connection Exit (N Position and 2/3/4 Positions Determine "Where It Extends Out")

For R&D readers, the real key is not whether "piperidine" is present, but where the connection arm extends from:

1. N Position: Often used for adjusting the polarity and salting ability, and it's easiest to modify charge strategies (free amine, acid-addition salt, quaternary ammonium).

2. 2/3/4 Positions: Determines the spatial directionality of the connection arm and its "extension/folding" geometry. Position 2 is more likely to introduce chirality and stronger local stereochemical control, while positions 3/4 are often used to obtain different extension vectors.

These choices impact:

1. The overall molecular geometry (extension/folding and substituent direction)

2. Polarity distribution and salt formation

3. Metabolic susceptibility and stability trends (this part highly depends on specific substitution and exposure level, which should be verified with examples and data)

4.Typical Application Lines

In the previous sections, we have clarified the three controllable variables of piperidine: charge state, three-dimensional conformation, and connection exit. Below, we explain the scenarios where piperidine is commonly used in real R&D tasks and which variable to focus on first.

A. Medicinal Chemistry: Making Physicochemical Properties and Spatial Occupation Iteratively Optimizable

Piperidine and its chiral derivatives are very common in approved drugs and lead structures, often used to address both physicochemical properties and three-dimensional occupation issues simultaneously.

1. If your core issue is solubility, salt formation, distribution, and exposure fluctuations

→ Start with charge strategy: Focus on the N position morphology and salt type selection (free amine/acid-addition salt/quaternary ammonium, representing reversible adjustment and permanent charge routes).

2. If your core issue is selectivity, unstable binding poses, or difficulty in structure-activity relationship convergence

→ Start with three-dimensional shape and exit: Use 2/3/4 position substitution and stereochemistry to alter connection directions; introduce bicyclic/bridged/fused ring structures when more fixed occupation is required.

B. Synthetic Chemistry: Classic Base Conditions in Fmoc Deprotection

In Fmoc solid-phase peptide synthesis, 20% piperidine/DMF is one of the classic deprotection conditions. Methodological studies often use this as a reference baseline, then compare alternative amines or optimize conditions.

1. Piperidine provides stable and repeatable deprotection capability, making it commonly used as a benchmark condition.

2. However, its process cost (smell and safety, potential side reactions with sensitive sequences/functional groups) should be considered, and as a result, alternative solutions and condition tuning routes are often found in the literature.

C. Materials and Radical Chemistry: HALS Structural Motif and TEMPO-type Nitroxyl Free Radicals

1. HALS (Hindered Amine Light Stabilizers)

A large number of HALS are derivatives of tetramethylpiperidine, used in polymers to suppress light oxidation degradation related chain processes. Mechanism and applicability have been systematically reviewed.

2. TEMPO and Nitroxyl Free Radicals

TEMPO, a stable nitroxyl free radical derived from piperidine, is commonly used in oxidation systems such as alcohol oxidation, radical-related methodologies, and in some materials/polymer radical processes.

5.Quick Navigation Table: When to Consider Piperidine?

R&D Need	Value Piperidine Might Provide	Priority Aspects to Check (3 Key Points)
Need easier salt formation, convenient formulation, while retaining some hydrophobic volume	Protonable six-membered amine ring, charge state can switch with conditions	Protonation ratio at target pH (pKaH as starting point); salt type and ion selection (crystal form, hygroscopicity, stability); solubility and formulation stability (check logD/permeability if needed)
Need clearer three-dimensional occupation (more controllable than flexible chains)	Six-membered ring provides a relatively defined three-dimensional profile (substituent directions predictable after modification)	Substitution at 2/3/4 positions and stereochemistry; axial/equatorial preference and conformation flip impact; need for further conformation restriction
Want to systematically scan connection points and directions for SAR	Substitution position determines connection arm vector	N-position vs. 2/3/4 position exit choice; potential introduction of chirality and cis/trans; use of bicyclic/bridged/fused rings to fix shape
Polymer/material system requires light aging resistance	Tetramethylpiperidine derivatives (HALS) are a classic stabilization route	Additive migration/volatility and compatibility; processing temperature and long-term thermal stability; compatibility with system acids/metal impurities/flame retardant systems
Need radical process control or mild oxidation methodology tool	TEMPO and piperidine-type nitroxyl free radicals as radical mediation/catalysis components	Suitable substrates and selectivity; required oxidation system and byproduct control; post-treatment and residue management (smell/color/purification difficulty)

6.Checklist: When You Get a Piperidine-like Structure, Check These 5 Things First

1. What is the charge strategy: Free amine, acid-addition salt (piperidinium salt), or quaternary ammonium piperidinium (determines if charge can switch with pH)?

2. Will it mainly be charged under target conditions: Check the conjugate acid pKaH and evaluate protonation ratio at the target pH (do not rely on a single pKa number).

3. Where is the connection exit: At the N-position or at 2/3/4 positions? Is chirality or cis/trans involved (determines connection direction and how cleanly it can be controlled)?

4. Is the conformation fixed: Is it bicyclic/bridged/fused ring (fixed shape often aids attributions but increases synthesis complexity and cost)?

5. Clarify the purpose: Is it for property optimization and spatial occupation comparison, synthetic reagent/process additive, or material stability/radical tool (avoid interpreting structural tools as the active entity)?

7.Piperidine and Its Derivatives Product Navigation Table (Tables 1–5): Quick Location Based on "Research Tasks/Experimental Scenarios"

Research Task / Experimental Need	Suggested Table to Check First	Why Start with This Table	Common Additional Linkage
Fmoc Solid-Phase Peptide Synthesis: Need to deprotect Fmoc / Handle resin terminal groups (Standard 20% piperidine/DMF)	Table 1	Table 1 includes piperidine solution (20% in DMF), as well as general platform reagents highly related to "peptide synthesis/deprotection."	Need to introduce "conformation-limited residues" for peptide comparison → Table 2
Methodology/Mechanism: Want to use TEMPO for alcohol oxidation or radical process verification (inhibition, capture, catalyzed oxidation)	Table 1	Table 1 focuses on TEMPO, 4-Hydroxy-TEMPO, 4-Oxo-TEMPO, etc., common "radical toolkit" entries for materials/mechanism studies	Need to "attach TEMPO to the molecule" for derivatization → Common starting point from available linking sites (4-Hydroxy-TEMPO already covered in Table 1); if also need piperidine connection arm → Table 3
Need a strong base but want to avoid nucleophilic side reactions: For selective deprotonation/low-temperature metalation (e.g., after lithiation, capturing electrophiles)	Table 1	Table 1 includes typical non-nucleophilic strong base systems like TEMP / LiTMP, key choices for "reaction condition level" selection	Target substrate is piperidine building block with further substitution/connection → Table 4/3
Material formulation: Need light-oxidation aging resistance/weather stability (HALS)	Table 1	Table 1 includes typical HALS products and precursors (hindered amines and their sebacate esters), directly addressing material stabilization needs	Need further structural modification/attachment for grafting → Often back to "derivable handle" approach (Table 1/3)
Pharmaceutical Chemistry/Chemical Biology: Want to introduce piperidine as a conformation-limited residue/amino acid-like fragment (substitution/comparison/conformation fixation)	Table 2	Table 2 focuses on pipecolic/nipecotic/isonipecotic "amino acid-like" carboxylic acids and their protective forms, best for "conformation-limited comparison" and coupling library building	If further operational ease is needed (Boc/Fmoc protection, esterification intermediates) → Covered inside Table 2; if additional polar handles (amino/hydroxy) are needed → Table 3
Peptides/Peptide Analogues: Need Fmoc monomer directly usable for SPPS (including chirality)	Table 2	Table 2 includes Fmoc-D-Pip-OH and (S)-Fmoc-piperidine-2-carboxylic acid, directly corresponding to SPPS materials	To further optimize "properties/solubility/salt type" → Commonly linked to Table 3/5
Modular Assembly/Connection Arms: Need piperidine with hydroxymethyl or aminomethyl for easy attachment of aromatic rings/heterocycles/side chains	Table 3	Table 3 is a "functionalized piperidine handle library": 3-hydroxy, 4-hydroxy, 4-aminomethyl, along with corresponding Boc protection/salt types, ideal for connection arms and bifunctional coupling	Need to further activate the handle into a leaving group for substitution → Table 4
Want to significantly improve water solubility/introduce permanent anionic characteristics: Need sulfonated piperidine fragment	Table 3	Table 3 includes piperidine-4-sulfonic acid, one of the most direct and powerful structural means for "water solubility/ionic characteristics"	If also need to adjust pKa/hydrophobicity balance (not just improving water solubility) → Table 5
Want to use "nitrile group" as a convertible handle: Place a CN first, then reduce/hydrolyze to amine/acid/amidate	Table 3	Table 3 includes 4-cyanopiperidine and its hydrochloride, suitable for use as "multi-directional branching intermediates" in route design	If your target is actually "halogenate first, then introduce CN or other groups" → Table 4
Want to quickly synthesize a series of 3- or 4-substituted piperidine comparisons: Hope to introduce different nucleophiles in one SN2 step	Table 4	Table 4 focuses on 3/4-halogenated piperidine (including HBr salt, Boc protection, I/Br/Cl different leaving groups), best for "quickly scanning a set of substitution comparisons"	After substitution, typically need: ① Deprotect Boc/salt formation → Table 1 (piperidine salts/conditions) ② Introduce polar handle/connection arm → Table 3
More concerned with "reaction reactivity": Want a stronger leaving group, faster reactions (especially difficult-to-substitute substrates)	Table 4	Table 4 includes iodide (I), relatively more reactive, suitable for SN2/substitution with stronger driving force	If reactivity is too high, causing side reactions/control difficulties, you can switch to a milder leaving group (Br/Cl) still within Table 4; need more controlled amine protection → Choose Boc version (within Table 4)
More concerned with "reaction controllability/parallel library building": Want to protect N first, reduce side reactions, and later deprotect to obtain amine salt	Table 4	Table 4 includes various N-Boc halogenated piperidines, commonly used in "first coupling, then deprotect" parallel synthesis routes	Final salt type/feeding stability and storage → Often return to Table 1 (salts/platform); introducing polar handles → Table 3
Pharmaceutical Property Optimization: Want to "fine-tune" pKa/conformation/hydrophobicity, without changing the piperidine core (common fluorination/CF₃ strategies)	Table 5	Table 5 focuses on F/2F/CF₃ piperidines (including hydrochloride salts), corresponding to "small changes to the same core → quick property scanning"	If you need "modular attachability/connection arms" instead of purely adjusting properties → Table 3/4
Suspecting metabolic/permeability/solubility bottlenecks: Need to use fluorine/CF₃ for systematic comparison to locate problem sources	Table 5	Table 5 provides a set of structurally similar fluorine/CF₃ piperidines, suitable for "structure-property" comparison (same backbone comparison)	If the final goal is to realize "synthesizable/attachable" routes → Commonly linked to Table 4 (substitution introduction) and Table 3 (polar handles)
Want to form salts/improve storage stability/better weighing and feeding (especially amines prone to volatilize/absorb water)	Table 1 (Preferred)	Table 1 includes piperidine hydrochloride and other "salt/platform" ideas, with many salt entries in other tables as well; first clarify "whether a salt form is needed" to save time	Specific structural building blocks still return to Table 2/3/4/5 based on use; need fluorinated salt type → Table 5

Table 1｜Basic Reagents / Solvent Platforms / Strong Bases and Radical Tools (Commonly Used in Processes and Methodology)

Category	CAS Number	Aladdin Catalog No.	Name	Purity/Specification	Product Features and Applications
Basic Parent Core/Common Reagents	110-89-4	P1506348	Piperidine solution	20% in DMF	Classic deprotection reagent for Fmoc solid-phase peptide synthesis: 20% piperidine/DMF is used to remove Fmoc; also a common organic base/capture agent in organic synthesis (note "easy to manufacture/control" property for compliant use).
Basic Parent Core Salt	6091-44-7	P194173	Piperidine hydrochloride	≥98%	Stable salt form of piperidine: easy for weighing, storage, and transportation; can release free piperidine under basic conditions or directly used as piperidinium salt for acid-base regulation/salt formation screening and reaction control.
Lactam (Piperidone)	675-20-7	P160613	2-Piperidone	≥98% (GC)	Piperidine lactam platform: can be used as an intermediate for N-substitution, α-functionalization, etc.; also reducible back to piperidine-based derivatives for drug blocks and molecules containing lactam backbone.
Polar Solvent/Reagent	931-20-4	N335945	N-Methyl-2-piperidone	≥95%	High-boiling, strong polar non-protonic solvent (NMP): commonly used for polymerization, coupling, substitution systems requiring high solubility; also used in materials/membrane preparation and high-temperature reaction media (note safety and regulatory requirements).
Hindered Strong Base/Non-nucleophilic Base	768-66-1	T133588	2,2,6,6-Tetramethylpiperidine (TEMP)	≥98% (GC)	Hindered non-nucleophilic base: used in systems requiring "strong base but minimal nucleophilic attack"; also a precursor for preparing LiTMP/NaTMP/KTMP metal amines, used in selective deprotonation/metalation and subsequent functionalization.
Strong Base/Metal Amine Base	38227-87-1	L469148	Lithium 2,2,6,6-Tetramethylpiperidide (LiTMP)	≥97%	Non-nucleophilic strong base (LiTMP): used for low-temperature selective deprotonation, metalation, and subsequent electrophile capture (e.g., α-functionalization, selective lithiation, etc.); commonly used in systems requiring "strong base but avoiding nucleophilic addition/side reactions."
Nitroxyl Free Radical	2564-83-2	T478495	TEMPO	≥99%	General nitroxyl free radical catalyst/intermediary: commonly used in selective alcohol oxidation (TEMPO/NaOCl, TEMPO/BAIB systems), free radical inhibition/capture; also used in polymer systems for radical control and mechanism studies.
Nitroxyl Free Radical (Hydroxy)	2226-96-2	H104510	4-Hydroxy-TEMPO	≥98%	TEMPO derivative with hydroxyl handle: used for TEMPO catalysis/intermediary oxidation and free radical research; 4-hydroxy facilitates ester/etherification for "immobilized TEMPO/connectable TEMPO labels," common in methodology and materials systems (e.g., electrochemical/polymer-related) development.
Nitroxyl Free Radical (Ketone)	2896-70-0	O135821	4-Oxo-TEMPO	≥95% (GC)	TEMPO oxidation derivative: used in free radical chemistry/oxidation systems and mechanism studies; 4-keto site serves as a further derivatization point (along with hydroxyl/amino derivatives for "functionalized TEMPO" toolbox).
Hindered Amine (HALS Precursor)	2403-88-5	H156928	4-Hydroxy-2,2,6,6-Tetramethylpiperidine	≥98% (GC)	Hindered amine backbone (HALS/nitroxyl free radical precursor): commonly used in synthesizing hindered amine light stabilizers or further oxidized to corresponding nitroxyl free radical derivatives; used in materials and radical chemistry to introduce antioxidant/stabilization structural units.
Material Additives	52829-07-9	B102211	Bis(2,2,6,6-Tetramethyl-4-piperidyl) Sebacate	≥98%	Typical HALS (Hindered Amine Light Stabilizer): used in plastics/coatings for weathering and light oxidation resistance (via radical process inhibition of chain degradation); often evaluated for stability windows in material formulations with UV absorbers, etc.

Table 2｜"Amino Acid-like" Carboxylic Acids/Esters & Fmoc/Boc Protecting Groups (Conformation-Limited Residues/Library Building Commonly Used)

Category	CAS Number	Aladdin Catalog No.	Name	Purity/Specification	Product Features and Applications
Conformation-Limited "Amino Acid-like" Building Blocks	498-95-3	P113283	3-Piperidinecarboxylic acid	Moligand™, ≥98%	Piperidine-3-carboxylic acid (Conformation-limited GABA/amino acid-like scaffold): commonly used in pharmaceutical/chemical biology for "conformation-limited" comparisons and derivatization (amide/ester/coupling); also found in neurotransmitter analog studies.
Conformation-Limited "Amino Acid-like" Building Blocks	498-94-2	I109586	Isonipecotic acid	Moligand™, ≥98%	Piperidine-4-carboxylic acid (rigid/fixed site): used to construct "carboxylic acid series with piperidine ring" (amidation, esterification, coupling library), often used as a conformation-limited residue/fragment replacement to adjust pKa, solubility, and conformation.
Protecting Groups	84358-13-4	B119065	1-Boc-isonipecotic acid	≥99%	N-Boc protected isonipecotic acid: Boc protection reduces amine end side reactions, enhances coupling controllability; often used for amidation/peptide-like coupling followed by Boc deprotection to yield target amine salts, suitable for parallel synthesis/fragment library.
Chiral "Amino Acid-like" Building Blocks	1723-00-8	H100528	D-Homoproline	≥99%	Chiral cyclic amino acid-like building block: used to introduce "ring-constrained/conformation-fixed" chiral centers (peptides/peptide analogs, conformation comparisons); commonly used to enhance conformation controllability and compare D/L configurations for activity and properties.
Conformation-Limited "Amino Acid-like" Building Blocks	535-75-1	S136371	DL-Pipecolic acid	≥98%	Pipecolic acid (racemic): used as "piperidine-2-carboxylic acid" scaffold reference/raw material; commonly used for quick reaction condition setup or fragment introduction and subsequent splitting/asymmetric route evaluation without requiring enantiomeric purity.
Conformation-Limited "Amino Acid-like" Building Blocks	3105-95-1	P106214	L-Pipecolic acid	≥98%	L-Pipecolic acid (conformation-limited residue): commonly used to replace proline in peptides/peptide analogs or introduce larger ring constraints; also used as a drug fragment to adjust conformation, basicity, and polarity distribution.
Amino Acid Protecting Groups	101555-63-9	I137410	Fmoc-D-Pip-OH	≥98%	Fmoc-protected chiral residue for solid-phase peptide synthesis: used to introduce D-configuration "piperidine carboxylic acid (pipecolic acid analog)" into peptide chains for conformation limitation/increased stability; coupled in the same process as conventional amino acids, convenient for conformation comparison peptide libraries.
Amino Acid Protecting Groups	86069-86-5	I134458	(S)-Fmoc-piperidine-2-carboxylic acid	≥97%	(S)-Fmoc-piperidine-2-carboxylic acid: commonly used monomer for solid-phase peptide synthesis/peptide-like molecules; used for conformation limitation and comparing chiral configurations' effects on conformation/activity/stability.
Carboxylic Ester Intermediates	1126-09-6	E123578	Ethyl isonipecotate	≥98%	Ethyl ester protecting group for isonipecotic acid: commonly used as "operable carboxylic acid equivalent" for amidation/substitution followed by hydrolysis to return to acid; suitable for routes that need functionalization at the amine end/ring before recycling the carboxylic acid site.

Table 3｜Polar Functional Group Building Blocks (Amino, Aminomethyl, Hydroxy, Sulfonic Acid, Nitrile, etc.; Including Boc/Salt Forms)

Category	CAS Number	Aladdin Catalog No.	Name	Purity/Specification	Product Features and Applications
High Polarity with Sulfonic Acid	72450-62-5	P612839	Piperidine-4-sulphonic acid	Moligand™, ≥97%	"Piperidine + sulfonic acid" high polarity fragment: used to introduce sulfonic acid/sulfonate in molecules to significantly increase water solubility and ionic characteristics; also used as a component with anionic sites for salt-type/ion-pair, or polarity/solubility window adjustments.
Functionalized Piperidine Alcohol	6859-99-0	H123509	3-Hydroxypiperidine	≥98% (GC)	Piperidine block with a hydroxyl group: the hydroxyl group provides a "further derivatization entry" (etherification/esterification/sulfonylation/oxidation, etc.), commonly used to adjust polarity, make connection arms, or construct 3-position substituted piperidine series for comparison.
Protecting Groups	85275-45-2	B121548	1-Boc-3-hydroxypiperidine	≥98%	Boc-protected hydroxypiperidine: Boc protection improves controllability of coupling/derivatization, commonly used for parallel synthesis; Boc deprotection releases amine site while retaining 3-hydroxy for further "connection arm/polarity regulation."
Functionalized Piperidine Alcohol	6457-49-4	P113833	4-Piperidinemethanol	≥98%	"Piperidine ring + alcohol" universal connection arm: Hydroxymethyl group can be further activated (halogenation/sulfonylation) for SN2 introduction, can also be oxidized to aldehyde/acid; commonly used to connect piperidine modules to aromatic rings/heterocycles or introduce longer connection arms.
Diamine/Connection Arm Blocks	7144-05-0	A136022	4-(Aminomethyl)piperidine	≥98% (GC)	Diamine connection arm: ring amine + external aminomethyl makes "two-point coupling/extended connection arms" (amide, urea, sulfonamide, etc.); commonly used to position piperidine ring as a solubility/basicity module and provide expandable connection sites.
Connection Arm Blocks	135632-53-0	T119042	4-(Boc-aminomethyl)piperidine	≥97%	Boc-protected "piperidine + aminomethyl" connection arm: commonly used to build extendable side chains and two-point coupling structures; Boc protection allows first coupling at one end, followed by deprotection for second-end connection, suitable for modular assembly.
Functionalized Piperidine Amine	13035-19-3	A103195	4-Aminopiperidine	≥98%	Ring amine + external primary amine: used to construct high-polarity/multi-point interaction fragments (amide/urea/sulfonamide, etc.); commonly used in drug discovery to provide "enhanced water solubility and additional coupling sites."
Functionalized Piperidine Amine	87120-72-7	A121575	4-Amino-1-Boc-piperidine	≥97%	4-Aminopiperidine (Boc-protected): typical "diamine scaffold" building unit for quickly introducing additional primary amine sites; commonly used in drug discovery to enhance coupling and form multi-point interaction structures.
Functionalized Piperidine Amine	184637-48-7	A121536	3-Amino-1-Boc-piperidine	≥97%	3-Aminopiperidine (Boc-protected): provides an additional primary amine "coupling handle," commonly used to build diamine/bidentate derivatives (amide, urea, sulfonamide, etc.); Boc protection enhances selectivity and controllability, suitable for parallel library building.
Functionalized Piperidine Amine	138060-07-8	A121533	3-Aminopiperidine dihydrochloride	≥97%	3-Aminopiperidine (dihydrochloride salt): provides "high-polarity diamine scaffold" in a stable salt form for easy storage and weighing; used in routes requiring strong nucleophilic amine coupling (usually first basified to release free amine, followed by selective protection/coupling).
Nitrile Piperidine Building Blocks	4395-98-6	C124465	4-Cyanopiperidine	≥97%	4-Cyanopiperidine: nitrile group is a common "convertible handle," which can be further converted to amine (reduction), acid/amide (hydrolysis/transformation); used to rapidly expand functional groups on the same piperidine scaffold.
Nitrile Piperidine Building Blocks	240401-22-3	P175866	Piperidine-4-carbonitrile hydrochloride	≥97%	4-Cyanopiperidine (hydrochloride salt): combines "piperidine basic center + nitrile handle"; hydrochloride salt is convenient for storage and weighing, and can be basified to release free amine for coupling, while the nitrile site can be used for subsequent multi-directional functional group transformation.

Table 4｜Halogenated Activated Building Blocks (3/4 Position Halogenation; Including Boc Protection/Salt Forms; Primarily for SN2 Introduction)

Category	CAS Number	Aladdin Catalog No.	Name	Purity/Specification	Product Features and Applications
Halogenated Activated Building Blocks	54288-70-9	B123508	4-Bromopiperidine hydrobromide	≥98%	4-position brominated piperidine leaving group: commonly used with O/N/S/C nucleophiles for quick construction of 4-substituted piperidine series; hydrobromide salt aids in stable storage and reaction control (usually requires basification to release free amine/adjust selectivity).
Halogenated Activated Building Blocks	54288-72-1	B170900	3-Bromopiperidine hydrobromide	_	3-position brominated piperidine (hydrobromide salt): used for constructing 3-substituted piperidine series (region differs from 4-position, often leading to conformation/interaction differences); salt form is more stable, reaction usually requires basification/control pH to release active species for substitution.
Halogenated Activated Building Blocks	5382-18-3	C153867	4-Chloropiperidine	≥97% (GC)	4-Chloropiperidine activation site: used to build 4-substituted piperidine (SN2/substitution) and structural scanning; less active than bromine/iodine, suitable for more controllable conditions to compare the effect of different leaving groups on yield/selectivity.
Halogenated Activated Building Blocks	154874-94-9	T587407	N-Boc-4-chloropiperidine	≥97%	N-Boc-4-chloropiperidine: commonly used "controlled reaction activity" 4-position leaving group block; suitable for parallel synthesis of 4-substituted piperidine libraries (ether/amine/sulfide, etc.), deprotect Boc to yield target amine (can further optimize by forming salt).
Halogenated Activated Building Blocks	180695-79-8	B121573	4-Bromo-N-Boc-piperidine	≥97%	4-Bromo-N-Boc-piperidine: 4-position bromine ideal for efficient substitution to build 4-substituted piperidine libraries; Boc protection enhances reaction cleanliness and aids in later deprotection/salt formation, commonly used for rapid SAR scanning.
Halogenated Activated Building Blocks	860765-00-0	I729980	4-Iodo-piperidine	≥97%	4-Iodopiperidine strong leaving group block: suitable for substitution with high reactivity (easier substitution); commonly used for rapid synthesis of 4-substituted piperidine and to compare yields and side reactions under different nucleophiles/conditions.
Halogenated Activated Building Blocks	301673-14-3	T161641	N-Boc-4-iodopiperidine	≥97% (GC)	N-Boc-4-iodopiperidine: iodine as a strong leaving group, suitable for rapid 4-position substitution series construction (with O/N/S/C nucleophiles); Boc protection improves reaction controllability, convenient for parallel library building followed by deprotection to yield amine salts.

Table 5｜Fluorine/CF₃ Substituted Piperidine Building Blocks (pKa/Conformation/Hydrophobicity/Metabolic Stability Adjustment)

Category	CAS Number	Aladdin Catalog No.	Name	Purity/Specification	Product Features and Applications
Fluorine Piperidine Building Blocks	144230-52-4	D131742	4,4-Difluoropiperidine hydrochloride	≥98%	4,4-Difluoropiperidine for "property adjustment": Difluorine substitution is commonly used for system regulation of basicity (pKa), conformation, and lipophilicity, as well as improving metabolic stability/conformation-activity relationships; hydrochloride salt form is convenient for weighing and subsequent salt formation/coupling.
Fluorine Piperidine Building Blocks	496807-97-7	W136180	3,3-Difluoropiperidine hydrochloride	≥97%	3,3-Difluoropiperidine (hydrochloride salt): Difluorine substitution is used for system regulation of basicity and conformation (C-F inductive effects), commonly found in pharmaceutical property optimization; hydrochloride salt enhances ease of handling and storage stability.
Fluorine/CF₃ Substituted Piperidine Building Blocks	768-31-0	T469662	3-(Trifluoromethyl)piperidine	≥97%	3-CF₃ piperidine: CF₃ is commonly used to increase hydrophobicity, alter electronic effects, and impact pKa/metabolism; suitable for "same backbone with different substitution" property scanning (solubility/permeability/stability/selectivity).
Fluorine/CF₃ Substituted Piperidine Building Blocks	155849-49-3	T132002	4-(Trifluoromethyl)piperidine hydrochloride	≥97%	4-CF₃ piperidine (hydrochloride salt): used to significantly alter hydrophobicity and electronic effects without changing the backbone; commonly used for "site-fixed (4-position)" conformation/property comparison series construction.
Fluorine Piperidine Building Blocks	737000-77-0	F177311	3-fluoropiperidine hydrochloride	≥97%	3-Fluoropiperidine hydrochloride: Monofluorine substitution is a common "fine-tuning knob" used to adjust basicity, conformation, and metabolism; hydrochloride form aids in handling and subsequent coupling/salt screening.
Fluorine Piperidine Building Blocks	57395-89-8	F171054	4-Fluoropiperidine hydrochloride	≥97%	4-Fluoropiperidine hydrochloride: 4-position fluorine substitution is commonly used for fine-tuning conformation and pKa, while maintaining the backbone and adjusting properties; hydrochloride form facilitates reaction feeding and subsequent salt/crystallization process exploration.

Note: The above are representative products from Aladdin. For more product specifications, please refer to the product list at the end of the article or search by "product name/CAS/catalog number" on Aladdin's official website.

For more related articles, please see below:

From Piperidine to Homopiperidine: How a Seven-Membered Nitrogen Ring Redirects Substituent Vectors and Shifts Salt Formation/Solubility Behavior (Tables 1–3)

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)

Substituted Azetidines in pharmaceutical chemistry, organic synthesis, and biochemistry