Late-Stage Fluorination Toolbox: “Minimally Invasive Upgrades” for Lead Candidates： Four “Fluorine Knobs” → Two major routes (electrophilic vs nucleophilic) → An ¹⁸F-PET tracer branch → Selection navigation & representative product list

In drug discovery, many molecules end up stuck in the same awkward spot: potency is good, but exposure is insufficient; selectivity looks fine, but metabolism is too fast; in vitro is beautiful, yet in vivo distribution is disappointing. In those moments, you usually don’t want to rebuild the molecule from scratch—you want the smallest structural change that can deliver the largest property shift.

Fluorine (F) is one of the most frequently used—and most easily misunderstood—modifications. It can significantly influence a molecule’s electron distribution, conformational preference, and metabolic fate with only a subtle structural change. But it’s crucial to emphasize: fluorine does not guarantee optimization. It is better viewed as a wrench/knob—turned correctly it may improve DMPK and/or potency; turned incorrectly it may reduce solubility, raise lipophilicity too much, or even introduce new metabolic and safety risks.

1. What can fluorine actually change?

Knob (mechanism)	What changes at the “molecular level”	Most commonly affected observables	Potential benefits	Common misconceptions / risks	How to close the validation loop
A. Electronic effects (pKa / polarity / reactivity)	Strong inductive effect + local dipole changes: alters electron density and acidity/basicity of nearby groups	pKa; overall polarity and polarity distribution (tPSA often unchanged, but logD / dipole / conformation-driven effective polarity & solvation can shift); solubility; binding mode changes	Tune pKa/ionization → impacts solubility & permeability; adjust local polarity → impacts binding & selectivity	Treating “F as a strong H-bond acceptor”: in most cases F in C–F is a very weak H-bond acceptor (often ignored in design). In rare cases (strong polarization/specific geometries) weak interactions may appear, but the dominant contributions more often come from inductive effects, dipoles, and conformational preorganization.	Pair measured/predicted pKa; logD, solubility; PAMPA/Caco-2 plus binding mode (crystal/computation)
B. Conformational effects (“pose control”)	Shifts local conformational preferences via gauche effects / hyperconjugation / dipole alignment, etc.	Conformer distribution; bound conformation; selectivity; exposure of metabolic sites	Lock a favorable conformation → higher potency/selectivity; “hide” metabolically vulnerable sites → potentially longer half-life	Conformational shifts can also expose metabolic sites or increase non-specific binding	Use NMR/computation to assess conformations; compare metabolic liabilities (metabolite profiling, CYP phenotyping)
C. Metabolic effects (pathway & “weak spot” reshuffling)	May “reinforce” a site, or redirect oxidation/hydrolysis priorities	CLint; t1/2; metabolite profile; CYP isoforms involved	Common tactic: introduce F near metabolically oxidizable sites to reduce clearance	Two realities: (1) metabolism can “reroute” elsewhere; (2) in some structures/systems C–F cleavage may occur, raising concerns such as (radio)defluorination or potential safety flags	Microsomes/hepatocytes + metabolite ID; when needed, assess reactive metabolites / monitor defluorination
D. (often accompanying) Physicochemical properties / distribution & exposure	F often simultaneously perturbs polarity, lipophilicity, and membrane permeability (direction depends on position/scaffold)	Oral exposure; tissue distribution; PPB; permeability/efflux	Sometimes improves permeability or distribution, increasing exposure	May decrease solubility, increase PPB, or “bias” distribution	Integrate in vitro ADME (solubility/permeability/efflux/PPB) with small-animal PK

Abbreviations

1. pKa: negative log of the acid dissociation constant; reflects acidity/basicity and ionization tendency.

2. logP: octanol/water partition coefficient (hydrophobicity of the neutral species).

3. logD: distribution coefficient at a specific pH (includes ionized species; commonly logD7.4).

4. PSA (tPSA): (topological) polar surface area.

5. HBA: hydrogen bond acceptor.

6. PAMPA: Parallel Artificial Membrane Permeability Assay (biased toward passive diffusion).

7. Caco-2: intestinal epithelial monolayer permeability model (human colon adenocarcinoma cell line).

8. NMR: Nuclear Magnetic Resonance.

9. CLint: intrinsic clearance (in vitro metabolic clearance metric).

10. t1/2: half-life.

11. CYP: cytochrome P450 enzyme system.

12. PPB: plasma protein binding.

13. ADME: absorption/distribution/metabolism/excretion.

14. PK: pharmacokinetics.

Extra note on C (metabolism), especially for ¹⁸F-PET: you must pay special attention to radiodefluorination. Once free [¹⁸F]F⁻ is released in vivo, a common sign is increased non-specific uptake in bone, worsening imaging background. Therefore, the radiolabeling site must be not only “attachable,” but also preferably placed in a metabolically stable, low-defluorination-risk structural environment.

2. What is “late-stage fluorination”?

Many people misinterpret late-stage fluorination as “adding an F in the last synthetic step.” A more accurate definition is:

In the later part of a complex synthesis (near the final structural complexity), perform site-selective C–F bond formation or functional group interconversion on a scaffold that is close to the target structure—so you can explore SAR (Structure–Activity Relationship) and property space rapidly with minimal rework cost.

Its value is not “how impressive the fluorination reaction is,” but R&D efficiency:

1. Time-saving: you don’t need to rerun the entire synthetic route for every positional change.

2. Lower information cost: small changes with strong controls help you quickly identify what a site truly governs.

3. Closer to real candidates: conclusions are more transferable when you modify the actual complex scaffold.

3. Two major late-stage fluorination toolboxes: Electrophilic vs nucleophilic

Most late-stage fluorination routes can be grouped into two toolboxes:

1. Toolbox A: electrophilic / radical-type fluorination (more like “precision spot-welding an F onto the scaffold”)

2. Toolbox B: nucleophilic / deoxyfluorination (more like “replacing an existing part with C–F”)

3.1 Use “three questions” to choose the route

Q1. What type of carbon are you modifying?

(a) Electron-rich π systems / sites that can form enol(ate), enamine, and other “electron-rich handles”? → often start with A

(b) Existing “replaceable interfaces” such as –OH, OTs/OTf, etc.? → often start with B

Q2. Do you already have a ready entry point?

(a) Yes (–OH, leaving group) → B tends to hit more often

(b) No (only C–H) → A (especially the “radical/metal-catalyzed C–H fluorination” subset) is more common, but selectivity depends more on strategy

Q3. Which selectivity matters more to you?

(a) Regioselectivity (which position gets fluorinated): A often needs substrate bias/directing/catalytic control

(b) Chemoselectivity (not damaging other functional groups): B is typically more straightforward when a handle exists, but watch for elimination/rearrangement side paths

3.2 What’s the real difference between the two toolboxes?

Dimension	Toolbox A: Electrophilic / radical-type fluorination	Toolbox B: Nucleophilic / deoxyfluorination
Core logic	When no ready “handle” exists, use substrate electronics or catalytic systems to introduce F onto the target carbon. Mechanistically, this may be a two-electron electrophilic process or a SET/radical pathway (e.g., F-atom transfer).	First prepare a “replaceable handle” (leaving group or –OH), then use F⁻ for substitution/deoxygenation to convert that site into C–F. (Not only ROH→RF deoxyfluorination, but also SN2 (alkyl)/SNAr (aryl) nucleophilic fluorination when leaving groups exist.)
Most commonly used when you have…	No obvious handles like OTs/OTf/–OH, but the molecule contains: (1) electron-rich arene/heteroarene; (2) alkene; (3) sites that form enol(ate)/enamine; or you want to probe whether a C–H site can be fluorinated directly	A clear “entry point” is already present: (1) leaving groups such as OTs/OTf (for F⁻ substitution); (2) alcohol –OH (very common: –OH → –F deoxyfluorination)
What mainly determines “where F lands”?	Mainly: (1) which position is easiest to activate (more electron-rich / easier intermediate formation); (2) whether directing/catalysis can pull the reaction toward a specific site; (3) conditions bias toward two-electron vs SET/radical channels (affecting regioselectivity and side reactions)	Mainly: (1) the handle position “locks” the site; (2) leaving group/activation determines whether substitution proceeds; (3) competing pathways (elimination/rearrangement/retention vs inversion) determine cleanliness and stereochemical fidelity
Typical advantages (R&D view)	Good for quickly answering on complex scaffolds: which electron-rich sites / which C–H sites are worth making fluorinated analogs—especially when no handle exists	Very high-frequency for “minimal change, strong perturbation” at common motifs like –OH; handle is explicit, controls are strong, ideal for SAR/property scanning
Common problems / risk points	(1) Not always a single “F⁺” mechanism: many N–F systems can involve SET/radicals; (2) N–F reagents can be somewhat oxidizing—sensitive substrates may show oxidation-related side reactions or poor functional group tolerance	(1) Deoxyfluorination commonly suffers elimination (alkene formation) impacting yield/purity; (2) some reagents pose significant safety/exotherm hazards (especially DAST-class), requiring strict safety practices

3.3 Toolbox A | Electrophilic / radical-type fluorination

1. Core decision rule: When the molecule lacks ready handles like –OH/OTs/OTf, route A is often used to introduce F on electron-rich π systems (arenes/heteroarenes, alkenes, enol(ate)/enamine-related sites) or certain C–H positions.

2. Boundary note: Many reactions involving N–F reagents may proceed via SET/radical pathways rather than purely “two-electron electrophilic substitution/addition.”

3. Why N–F reagents (Selectfluor, NFSI) dominate: Compared with earlier harsh fluorinating systems (e.g., F₂), N–F reagents are generally easier to handle and more amenable to catalyst/condition design to achieve workable selectivity; in late-stage settings, they often provide a practical path to quickly generate SAR-comparable analogs.

4. Selectfluor vs NFSI (rule-of-thumb differences):

(a) Selectfluor: higher reactivity and broader coverage; in some systems, more prone to oxidation/SET-related side reaction signals (be more cautious with sensitive substrates).

(b) NFSI: relatively milder; often used when probing for “steadier” functional-group compatibility (still substrate- and catalysis-dependent).

5. When to prioritize route A:

(a) Probe whether an electron-rich ring/site on a complex scaffold can be fluorinated, and quickly read potency/metabolic trends;

(b) Generate a series of fluorinated analogs with similar substitution patterns from one core for SAR scanning;

(c) For non-activated C–H sites, success often depends on directing/catalysis/radical strategies—selectivity is generally less straightforward than “handle-based replacement.”

6. Safety reminder: Strong fluorinating systems (e.g., F₂) are highly hazardous; this article discusses route logic and selection principles only, not operational procedures.

3.4 Toolbox B | Nucleophilic / deoxyfluorination

1. Core decision rule: If a ready “entry point” exists, route B is more direct:

(a) leaving group (OTs/OTf, etc.) → substitution by F;

(b) even more commonly, deoxyfluorination: alcohol –OH → –F.

2. Why deoxyfluorination is crucial in late-stage work: –OH is common and easy to access in complex molecules (natural products, sugars, steroids, chiral building blocks, etc.). Replacing –OH with –F is a classic “minimal change, strong property perturbation” strategy.

3. DAST: effective but high-risk: DAST is a classic deoxyfluorination reagent, long recognized for notable safety/exotherm risks; on certain substrates it more readily competes via elimination (alkene formation), affecting purity and stereochemical integrity.

4. Safety reminder: Literature and vendors often describe Deoxo-Fluor, XtalFluor, PyFluor, etc. as “easier to handle / more controllable / more thermally stable (relative to DAST),” but that does not mean “safe.” These remain highly reactive fluorinating systems; exotherms, decomposition, and side reactions depend strongly on substrate and conditions. Practical use must follow SDS guidance and institutional EHS requirements.

5. PyFluor: a modern “more controllable” upgrade concept: As a newer deoxyfluorination option, PyFluor is often positioned as more “engineering-friendly,” with improved thermal stability/controllability and reduced headaches from elimination-type side reactions.

6. What does the substitution really change? Deoxyfluorination can be viewed as replacing a hydrogen-bond donating/accepting –OH with a strong dipole C–F that has different conformational preferences and may reroute metabolism. It is therefore widely used when you want to shift properties noticeably without major scaffold redesign—but still requires DMPK and metabolite profiling to close the loop.

4. The “Second Main Line” of Fluorine Magic: ¹⁸F-PET Is Not About Improving Efficacy, but About Giving a Molecule a “Trackable Barcode”

4.1 ¹⁸F is one of the most commonly used radionuclides in PET—largely because its physical window is “just right”

1. Half-life ~110 minutes (109.7 min): long enough to support radiochemical synthesis of reasonable complexity, QC, and the logistics from the production site to the imaging site.

2. Mature production pathway: ¹⁸F is typically produced by a cyclotron. A common route is proton irradiation of an enriched ¹⁸O target, generating [¹⁸F]F⁻ (in aqueous solution) as a radiochemistry “universal starting point.” This also means that practical ¹⁸F labeling often relies on a mature process chain (target material, purification, automated modules, QC systems).

Note: ¹⁸F radiochemistry must be performed in compliant radiation facilities under standardized procedures.

4.2 Three typical routes for late-stage ¹⁸F labeling

In late-stage radiolabeling, the core demand for ¹⁸F is very clear: introduce the radioactive atom as close to the end as possible (to minimize decay loss), while keeping precursor design flexible and workflows more platform-ready / automatable.

Reminder: This article uses three of the most common “late-stage labeling logics” as a conceptual guide. Beyond these, ¹⁸F radiochemistry also frequently uses iodonium/sulfonium salt precursors, aryl-metal precursors, and platform strategies such as ¹⁸F-fluoroalkylation or group labeling via “handles/precursor groups” (not expanded here).

A one-table overview to “get the three routes at a glance”

Route	Typical “precursor entry” needed	The main pain point it addresses	Key challenges / boundaries
1) Improved SNAr-type nucleophilic aryl radiofluorination	An aryl/heteroaryl ring with a leaving group and an “activated” ring system; usually starts from [¹⁸F]F⁻	Makes the most classic, reliable SNAr more controllable and better aligned with realistic process windows	The solubility/water content/coordination state of [¹⁸F]F⁻ strongly impacts its “effective nucleophilicity” and reaction window; not all arenes are suitable
2) Cu-mediated aryl boronate ester (aryl-BPin) → ¹⁸F-aryl	The molecule can be converted to / already contains an aryl-BPin handle	Replaces the “entry handle” with a medicinal-chemistry-common BPin handle, greatly expanding the range of molecules that can be made into imaging versions; supports platforming/automation	Relies on metal-mediated systems; substrate and functional-group compatibility must still be evaluated (but overall a very practical “platform route”)
3) Direct ¹⁸F fluorination of arene C–H (photoredox, etc.)	When it’s inconvenient to pre-install leaving groups or handles, and you want to label arene C–H directly	“Liberates precursor design”: reduces the burden of redesigning precursors solely for radiolabeling	The applicability boundary depends more on substrate structure and selectivity control; usually requires more specific substrate evaluation and validation

Route 1 | Improved nucleophilic aryl radiofluorination (SNAr, etc.): making [¹⁸F]F⁻ “more usable”

1. What it is: One of the most traditional and reliable ideas—use [¹⁸F]F⁻ for nucleophilic aromatic substitution (SNAr) or related nucleophilic aryl radiofluorination on aryl/heteroaryl rings, replacing a leaving group on the ring (often best suited to activated aryl/heteroaryl systems).

2. Why it needs “improvement”: In radiochemistry, the performance of [¹⁸F]F⁻ is highly sensitive to solubility, water content, and coordination state, which directly determines its effective nucleophilicity and the workable reaction window—this is not a detail; it is often decisive.

3. Modern trend: Many engineering-oriented strategies aim to turn [¹⁸F]F⁻ into a more controllable, platform-friendly form so that classic SNAr can run reliably within real-world process constraints.

4. Representative example: The Sanford group has reported concepts such as introducing [¹⁸F]F⁻ into reactions in a more organic-phase-usable, platform-friendly quaternary ammonium salt form (e.g., [¹⁸F]Me₄NF / [¹⁸F]TMAF), which can serve as an example of “making [¹⁸F]F⁻ more usable.”

5. One-sentence takeaway: This route is about making classic SNAr more controllable and more platformable.

Route 2 | Cu-mediated aryl boronate ester → ¹⁸F-aryl: using the more common “BPin handle” as the entry point

1. What it is: Use a Cu-mediated system to convert aryl boronate esters (aryl-BPin) into ¹⁸F-aryl products.

2. Why it matters: BPin/boronic precursors are highly common and accessible in medicinal chemistry, so in practice this route often means:

(a) More parent molecules can more easily be turned into corresponding ¹⁸Flabeled PET radiotracer versions;

(b) It is more conducive to repeatable, modular workflows (especially friendly to platforming/automation).

3. One-sentence takeaway: It replaces rare/harsh precursor types with a more general BPin handle, greatly broadening the usable scope.

Route 3 | Direct ¹⁸F fluorination of arene C–H (photoredox, etc.): letting some molecules “skip one precursor functional group”

1. What it is: The goal is straightforward—bypass the requirement to pre-install leaving groups/handles and directly introduce ¹⁸F at an arene C–H position.

2. Value: Expands the precursor design space—some molecules may not need an entirely separate, complex precursor redesign solely for radiolabeling.

3. Boundary note: This route often depends more strongly on substrate structure and selectivity control; in real projects it requires more specific substrate evaluation and validation. It is more like “opening a new door,” but not necessarily “a standardized, platformable workflow.”

4. One-sentence takeaway: Conceptually it is the most “precursor-liberating,” but its applicability depends more on structure/system and requires more cautious feasibility judgment.

5. Route Navigation Table: when you face a specific R&D problem, which late-stage fluorination should you check first?

R&D scenario	Likely priority toolbox	Why it matches better	Key “outcome metrics” to watch
Potency is decent, but in vivo exposure is low / metabolism too fast; you want to “turn the property knob” quickly without redoing the whole synthesis	Overall late-stage fluorination strategy (prioritize finding modifiable sites)	Minimally invasive changes on near-final scaffolds deliver the highest information density	Solubility; logD; liver microsomal stability; plasma protein binding; in vivo exposure
The molecule contains an aryl ring / electron-rich site; you want to rapidly make a series of fluorinated analogs for SAR scanning	Electrophilic fluorination (N–F systems)	More straightforward at electron-rich sites; good for probing “site/substitution pattern” space	Trends in potency/selectivity; whether oxidation-related side reaction signals appear
The molecule contains –OH (natural products/steroids/sugars/chiral building blocks, etc.); you want “minimal change but obvious property shift”	Nucleophilic deoxyfluorination (ROH → RF)	–OH is one of the most common modifiable handles; swapping to –F strongly changes H-bonding and dipole features	Stereochemical retention vs inversion; elimination side reactions; overall solubility/permeability shifts
You are not trying to optimize efficacy, but to “track where the molecule goes” (distribution/targeting/tumor uptake)	Late-stage ¹⁸F-PET labeling routes	¹⁸F has a short half-life—requiring fast, QC-compatible, scalable workflows; route choice determines practical deliverability	Radiochemical purity; molar activity; residual controls; automation/reproducibility

6. Is fluorination always better?

FAQ 1: The C–F bond is strong—does that automatically mean “more metabolically stable”?

Not necessarily. Many people assume “C–F is strong, so adding F must improve metabolic stability.” In reality, chemical and metabolic systems often do not try to break C–F directly; instead they may reroute to other sites or switch metabolic pathways:

1. Under certain chemical conditions or enzyme action, some structures may still undergo defluorination/cleavage, accompanied by fluoride release or formation of other metabolites with potential safety concerns.

2. In some cases, placing F near a metabolic soft spot does not stop metabolism—it may simply move metabolism to another position (or to a less desirable pathway).

Takeaway: Fluorination is more like a strong intervention in metabolic routing—it can help, but it can also introduce new problems.

FAQ 2: Is late-stage fluorination a “universal solution”? Can you directly introduce F at any site?

No. The core value of late-stage fluorination is efficiency and clean comparisons, but it is constrained by reality:

1. Site accessibility: can the desired position be reached and modified selectively under available chemistry?

2. Selectivity and functional-group compatibility: on complex scaffolds, side reactions and competing sites are often non-trivial.

3. Does the modified site truly control the property you care about? Even if F is installed successfully, it may not solve the key issue.

Therefore, late-stage fluorination is a strategy set (multiple entry points and methodologies), not a single reaction or a “universal last step.”

FAQ 3: How do you use data to clearly judge whether “fluorination works”? (the minimal validation loop)

1. First, state which knob you are turning.

Is it solubility? permeability? metabolic stability? conformation/binding mode? or distribution/exposure?

2. Then make a “minimal-change” fluorinated analog.

“Minimal change” = change only one structural variable at a time. Prioritize the most suspicious “knob site” (e.g., near a metabolic soft spot, an ortho position affecting pKa, or near a key binding conformation), and make one or a small set of clearly defined fluorinated controls (e.g., H → F or –OH → –F).

3. Finally, close the loop with the smallest set of metrics, for example:

(a) Solubility (or dissolution trend)

(b) logD (preferably fixed pH, e.g., 7.4)

(c) Metabolic stability (trend in liver microsomes/hepatocytes)

Takeaway: Fluorination is best viewed as a micro-adjustment of a property knob—not an automatic optimization. Only controlled comparisons and closed-loop data can tell you whether it improved things or made them worse.

7. Product Selection Navigation Table | For the Late-Stage Fluorination “Fluorination Toolbox,” Which Table Should You Check First? (Tables A–E)

Your need / scenario (typical question)	Which table to check first	Why this table is the best fit	What you will find in that table
You want electrophilic fluorination: introduce F on an aryl ring / electron-rich site; or use N–F reagents for late-stage “spot-weld-style” fluorination screening	Table A	Electrophilic fluorination reagents	Table A consolidates the key workhorse N–F electrophilic fluorinating reagents (Selectfluor, NFSI, NFPy salts) and strong electrophilic reagents (XeF₂). It’s the best starting point if you want to begin with “which fluorinating reagent to use.”
You want functional group interconversion / deoxyfluorination: convert an alcohol (–OH) to an alkyl fluoride (–F), or convert phenols to aryl fluorides; you want “minimal structural change with obvious property shifts” late in complex-molecule campaigns	Table B	Functional group interconversion / deoxyfluorination toolbox	Table B groups deoxyfluorination and the Ritter system together: DAST/Deoxo-Fluor/XtalFluor/PyFluor/AlkylFluor/PhenoFluor Mix—tools where “change the functional group and you can install F.”
You are building the nucleophilic fluorination / ¹⁸F radiochemistry “base platform”: need “fluoride source + base/buffer + phase-transfer/complexation + HF equivalents”; or you want system controls (anhydrous vs water-tolerant)	Table C	Fluoride sources / HF systems / bases & phase-transfer	Table C is the “platform table”: it brings together KF/CsF/TBAF, K₂CO₃/KHCO₃/Cs₂CO₃, K222, TBAB/TMAHCO₃, and HF·base (pyridine·HF, Et₃N·3HF). It’s ideal for assembling the system first.
You want method development & condition screening: need solvent systems, metal-salt catalysis (Ag/Cu), photochemistry/photocatalysis components; or you want to reproduce/explore the literature reaction window	Table D	Reaction media/solvents & catalysis/photochemistry components	Table D is “reaction-condition hardware”: solvents (ACN/nitromethane/pyridine), metal salts (AgNO₃, Cu(OTf)₂), photochemical additives (TCB), photocatalysts (Ir complexes), etc.—useful for optimizing condition windows.
You need real complex scaffolds for late-stage fluorination feasibility checks / control experiments: use drug or natural-product standards to evaluate site selectivity, functional-group compatibility, and whether fluorination is worth pursuing	Table E	Representative substrates / drug standards	Table E focuses on “test substrates/control molecules”: bile acids such as cholic acid/lithocholic acid, estrone (phenolic substrate), and real drug standards (celecoxib/roflumilast/fluticasone propionate/ivermectin) for method transfer and validation.

Table A | Electrophilic Fluorination Reagents (N–F Reagents & Strong Electrophilic Fluorinating Agents)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features or applications (fluorination toolbox–related)
Electrophilic fluorinating reagent (solid, high-risk/strongly oxidizing)	13709-36-9	X475182	Xenon difluoride	PrimorTrace™, ≥99.99% metals basis	Classic solid electrophilic fluorinating agent; used for electrophilic fluorination condition scouting/controls (strong oxidant—requires professional safety and materials-compatibility assessment).
Electrophilic fluorinating reagent (N–F, mild)	133745-75-2	F122293	N-Fluorobenzenesulfonimide	≥97%	Classic mild N–F electrophilic fluorinating reagent (NFSI); generally good functional-group tolerance; commonly used in late-stage electrophilic/radical fluorination methodology for complex molecules.
Electrophilic fluorinating reagent (N–F, strong)	107263-95-6	F156745	1-Fluoropyridinium trifluoromethanesulfonate [fluorinating reagent]	≥96%	N-fluoropyridinium salt electrophilic fluorinating reagent (NFPy·OTf): relatively high reactivity; useful for expanding electrophilic fluorination conditions and probing fluorination sites.
Electrophilic fluorinating reagent (N–F, general-purpose)	140681-55-6	S101457	N-Fluoro-N'-(chloromethyl)triethylenediamine bis(tetrafluoroborate)	≥95%	Selectfluor (F-TEDA-BF₄): widely used, general-purpose N–F electrophilic fluorinating reagent; a common workhorse for rapid condition/site screening in late-stage electrophilic/radical fluorination on complex scaffolds.

Table B | Functional Group Interconversion / Deoxyfluorination Toolbox (DAST / Deoxo-Fluor / XtalFluor / Ritter Systems, etc.)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features or applications (fluorination toolbox–related)
Deoxy/functional-group interconversion fluorinating reagent (solid, DAST alternative)	63517-29-3	X139125	(Diethylamino)difluorosulfonium tetrafluoroborate	Reagent grade	Common solid deoxyfluorination reagent (XtalFluor-E type); for alcohol → alkyl fluoride and related “functional-group interconversion” fluorination; convenient for weighing and scale-up screening.
Deoxy/functional-group interconversion fluorinating reagent (solid, DAST alternative)	63517-33-9	D578787	Difluoro-4-morpholinylsulfonium tetrafluoroborate	≥98%	Common solid deoxyfluorination reagent (XtalFluor-M type); for alcohol → alkyl fluoride conversion; often used as a more convenient alternative to DAST in practice.
Deoxyfluorination activation reagent (PyFluor)	878376-35-3	P160051	Pyridine-2-sulfonyl fluoride	≥98%	Core PyFluor reagent: activates alcohol sites and enables deoxyfluorination (late-stage functional-group interconversion fluorination); often used for mild screening on sensitive/complex substrates.
Deoxy/functional-group interconversion fluorinating reagent (Ritter system)	2043361-32-4	A151145	1,3-Bis(2,6-diisopropylphenyl)-2-fluoroimidazolium tetrafluoroborate	≥97%	Ritter-system fluoroimidazolium salt (common trade name: AlkylFluor): selectively activates alcohol sites for deoxyfluorination (ROH → RF); suitable for “minimally invasive replacement” in late-stage modification of complex molecules.
Ritter system (phenol → aryl F) key component / fluorinating complex	1648825-53-9	C587559	2-Chloro-1,3-bis(2,6-diisopropylphenyl)-1H-imidazolium chloride–cesium fluoride complex	30+ wt.% (2-Chloro-1,3-bis(2,6-diisopropylphenyl)imidazolium chloride)	Key component in typical “PhenoFluor Mix / related systems”: promotes phenol activation and works with CsF to enable aryl fluorination; suitable for functional-group interconversion routes in late-stage fluorination.
Deoxyfluorination reagent (classic, high-risk)	38078-09-0	D111067	Diethylaminosulfur trifluoride (DAST)	≥95%	Classic deoxyfluorination reagent (alcohols/carbonyls → fluorinated products); a common late-stage functional-group interconversion control, but thermally unstable with higher side-reaction risk (safety emphasized).
Deoxyfluorination reagent (DAST “improved”)	202289-38-1	B137512	Bis(2-methoxyethyl)aminosulfur trifluoride	≥90% (T)	Ritter-system fluoroimidazolium salt (often grouped into AlkylFluor-type reagent families): for alcohol-site activation and deoxyfluorination (ROH → RF); suitable for late-stage modification of complex substrates.

Table C | Fluoride Sources / HF Systems / Bases & Phase-Transfer (Common “Platform” Components for Nucleophilic Fluorination and ¹⁸F)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features or applications (fluorination toolbox–related)
HF system / fluorinating medium (high-risk)	7664-39-3	H116232	Hydrofluoric acid	Reagent grade, ≥40%	Classic “HF fluoride source / acidic medium”; used for building HF-based fluorination systems and HF·base adducts (strongly corrosive/high-risk—strict safety and compliance required).
HF system / fluorinating medium (more manageable HF form)	62778-11-4	H107606	Pyridinium poly(hydrogen fluoride)	Pyridine ~30%, hydrofluoric acid ~70%	“Olah reagent”–type HF complex; a more handleable HF fluoride source/acidic medium for HF-system fluorination and condition scouting (still requires strict protection).
HF system / manageable fluoride source (high-risk)	73602-61-6	T107263	Triethylamine trihydrofluoride	≥97%	Et₃N·3HF: a more handleable HF-equivalent fluoride source; used for fluorination/deoxyfluorination conditions where HF participation is needed (still corrosive).
Inorganic fluoride source (F⁻)	7789-23-3	P434124	Potassium fluoride	Suitable for analysis, ACS, premium grade	Fundamental nucleophilic fluoride source (F⁻); used in nucleophilic fluorination and, with complexing/phase-transfer systems, to improve fluoride “effective availability”; also used as a non-radioactive control for ¹⁸F workflows.
Inorganic fluoride source (F⁻, high nucleophilicity / often paired with activation systems)	13400-13-0	C755570	Cesium fluoride	UltraBio™, ≥99% (F)	Common strong nucleophilic F⁻ source; frequently paired with phase-transfer/activation systems or Ritter-type reagents; often seen in phenol/alcohol functional-group interconversion fluorination.
Organic fluoride source / phase-transfer salt (aqueous)	429-41-4	T106822	Tetrabutylammonium fluoride	75% in water	Common “soluble F⁻ source / phase-transfer-type fluoride”; used for nucleophilic fluorination or in combination with activation reagents (aqueous—good for water-tolerant systems; use caution for strictly anhydrous workflows).
Organic fluoride source (quaternary ammonium fluoride, hydrate)	17787-40-5	T102653	Tetramethylammonium fluoride tetrahydrate	≥98%	Soluble F⁻ source (quaternary ammonium salt); used as a control in water-tolerant or specific nucleophilic fluorination systems (contains crystal water—note for strictly anhydrous systems).
Inorganic base / fluoride activation	584-08-7	P485463	Potassium carbonate	Anhydrous, high purity, reagent grade, ≥99%	Common base for radiochemistry/nucleophilic fluorination; often used with phase-transfer/complexing agents to activate fluoride, adjust pH, and drive reactions.
Inorganic base / buffer salt	298-14-6	P432558	Potassium bicarbonate	Suitable for analysis, ACS, premium grade	Mild base/buffer; used in radiochemistry or nucleophilic fluorination to provide a gentler basic environment—useful for condition scouting with sensitive substrates.
Inorganic base / activator	534-17-8	C432848	Cesium carbonate	purum p.a., ≥98% (T)	Strong base/activator; often used to generate more reactive anions (e.g., phenolates), promoting nucleophilic fluorination or Ritter-system functional-group interconversions.
Radiochemistry / phase-transfer base salt (quaternary ammonium)	58345-96-3	T304060	Tetramethylammonium bicarbonate	60% in water	Common quaternary ammonium base salt in radiochemistry; can help build more “organic-phase-friendly” fluoride systems / buffered basic environments for ¹⁸F and nucleophilic fluorination workflow design.
Radiochemistry / phase-transfer base salt (quaternary ammonium)	17351-62-1	T770047	Tetrabutylammonium bicarbonate	≥95%	TBAB: commonly used as a phase-transfer/eluting base salt in ¹⁸F/nucleophilic fluorination; increases the usability of inorganic fluoride in organic media and provides a mild basic environment.
Phase-transfer / complexing agent (key radiochemistry auxiliary)	23978-09-8	H119933	4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane	≥98%	K 2.2.2 (K222, often called Kryptofix 2.2.2): complexes K⁺ to increase fluoride’s “effective availability/nucleophilicity”; a common complexing/phase-transfer additive in both ¹⁸F radiofluorination and conventional nucleophilic fluorination.

Table D | Reaction Media/Solvents & Catalysis/Photochemistry Components (Common for Method Development)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features or applications (fluorination toolbox–related)
Reaction solvent / medium	75-05-8	A433541	Acetonitrile (ACN)	For DNA synthesis, H₂O ≤10 ppm	Polar aprotic solvent; commonly used medium in nucleophilic fluorination/radiofluorination (including ¹⁸F) and drying workflows; low water content helps fluoride activation.
Reaction solvent / base / ligand	110-86-1	P111513	Pyridine	Anhydrous, ≥99.8%	Common base/solvent/ligand; can also form more handleable HF forms (e.g., pyridine·HF), useful for HF-system fluorination selection.
Reaction solvent / medium	75-52-5	N119666	Nitromethane (controlled precursor)	Anhydrous, ≥98.5% (GC)	Polar solvent; can be used to tune reactivity/selectivity in electrophilic fluorination systems (controlled material—use must be compliant).
Catalyst / metal salt (decarboxylation / radical-related)	7761-88-8	S197267	Silver nitrate concentrate	Dilute to 1 L for use; final concentration 0.1 M	Silver salts are commonly used as additives/catalytic components in “decarboxylation → radical → fluoride capture” systems; used for method verification and condition screening.
Metal catalyst (¹⁸F / aryl-F coupling)	34946-82-2	C100681	Copper(II) trifluoromethanesulfonate	≥98%	Representative metal-salt catalyst system for Cu-mediated coupling of aryl boronate esters/boronates with F⁻ (including ¹⁸F) to form aryl fluorides / ¹⁸F-labeled products.
Photochemistry additive / electron acceptor	712-74-3	T113727	1,2,4,5-Tetracyanobenzene	≥97%	Common photochemical electron acceptor / photosensitized-system component; used to build radical-pathway late-stage fluorination conditions (e.g., allylic C–H radical fluorination scouting).
Photoredox catalyst (methodology tool)	370878-69-6	T283137	Tris[5-fluoro-2-(2-pyridyl-κN)phenyl-κC]iridium(III)	≥95%	Typical Ir photocatalyst: used to generate radicals/activate substrates under photoredox conditions for late-stage fluorination or ¹⁸F methodology exploration (note metal residues/process QC when relevant).

Table E | Representative Substrates / Drug Standards (for Late-Stage Fluorination Method Validation & Controls)

Category	CAS No.	Aladdin Cat. No.	Name	Specification / Purity	Product features or applications (fluorination toolbox–related)
Complex substrate / case scaffold (steroid / bile acid)	81-25-4	C103692	Cholic acid, anhydrous	Analytical standard, ≥98%	Typical multifunctional steroid scaffold model; used for validating late-stage fluorination methodology (site selectivity/functional-group compatibility) and controls.
Complex substrate / case scaffold (bile acid derivative)	434-13-9	L106779	Lithocholic acid	Moligand™, ≥97%	Typical steroid bile-acid scaffold; used for late-stage fluorination condition screening and substrate-compatibility validation for decarboxylation/functional-group interconversion routes.
Complex substrate / case scaffold (phenolic substrate)	53-16-7	E105516	Estrone	Moligand™, analytical standard	Typical “phenol/arene” complex substrate; commonly used to test phenol → aryl fluoride functional-group interconversions (Ritter/PhenoFluor-type) and applicability.
Complex substrate / case-study drug	169590-42-5	C129279	Celecoxib	Moligand™, ≥99%	Real drug-scaffold standard; used for late-stage fluorination case validation (site selectivity and property controls on complex heteroaryl/aryl systems).
Complex substrate / case-study drug	162401-32-3	R126602	Roflumilast	Moligand™, ≥99%	Real drug-scaffold standard; can be used as a representative “candidate-molecule tracer/property-control” context in ¹⁸F/fluorination strategy discussions.
Complex substrate / case-study drug (fluorinated drug standard)	80474-14-2	F129894	Fluticasone propionate	Moligand™, ≥97%	Fluorinated drug standard; used to benchmark “fluorine effects on properties/metabolism” and for method validation (analysis/QC).
Complex substrate / case-study drug (macrocyclic natural product)	70288-86-7	I114320	Ivermectin	Moligand™, analytical standard	High-complexity macrocyclic substrate/standard; used to evaluate late-stage fluorination compatibility and method transferability in “multi-functional, sterically congested” systems.

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 the Aladdin website by product name/CAS.

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