Is 7-Ketolithocholic Acid the Same as UDCA Impurity F?
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7-Ketolithocholic acid is not a pharmacopoeial substance. No pharmacopoeia sets a monograph for it, and that is not a formality — it decides what a supplier can certify and what you can demand.
In the European Pharmacopoeia the compound appears in exactly one place: the related-substances test of the ursodeoxycholic acid monograph, where it carries the designation impurity F. In that role it is capped at 0.10 per cent, under the general criterion for unspecified impurities.
Buy it as a commercial intermediate and you are no longer buying against a pharmacopoeia at all. You are buying against a supplier's in-house specification. So the useful questions are narrower than they look: what is the pharmacopoeial identity, what limit applies when the material is present inside ursodeoxycholic acid, and which lines on a certificate of analysis actually carry compendial weight? This guide answers all three, then gives you a six-step check to run before you approve a batch.
One molecule, six names — and why that causes real procurement errors
The same compound reaches buyers under at least six different names. Suppliers use them interchangeably and specification sheets frequently carry only one. If the identity line on a certificate does not match the name on your purchase order, you are not looking at a formatting problem. You are looking at an unidentified material.
| Name | Type | Where you meet it |
|---|---|---|
| 7-Ketolithocholic acid (7-KLCA) | Catalogue name | Supplier catalogues, purchase orders, COA headers |
| 3α-Hydroxy-7-oxo-5β-cholan-24-oic acid | Systematic name | Regulatory dossiers, analytical documentation |
| Ursodeoxycholic acid EP impurity F | Pharmacopoeial designation | Ph. Eur. monograph, EP reference standards, supplier audit questionnaires |
| 7-Oxo-lithocholic acid · 7-keto-LCA | Literature synonym | Method studies, metabolism literature |
| 7-Keto-chenodeoxycholic acid · chenodeoxycholic acid oxide | Descriptive synonym | Commercial listings, process descriptions |
| Nutriacholic acid | Legacy literature synonym | Older papers; occasionally still on specification sheets |
The two "keto" names look contradictory but describe one structure. Chenodeoxycholic acid and lithocholic acid differ only by the hydroxyl group at C7. Oxidise C7 to a ketone on either skeleton and you arrive at the same molecule. That is why a buyer who orders under one name and receives documentation under the other may be holding a perfectly correct batch that fails an internal identity check on paperwork alone.
Registry identifiers are the reliable anchor: CAS 4651-67-6, molecular formula C24H38O4, molecular weight 390.56. Ask for all three on the specification sheet.
There is a second problem, and it bites more often than the naming does. Specification sheets in this category get copied from one another. In preparing this article I opened two supplier pages for ursodeoxycholic acid on the same day. One was headed "USP32/Ep8", the other "IP/BP/EP/USP". The two tables were word-for-word identical, and both carried European values — loss on drying not more than 1.0 per cent, heavy metals not more than 20 ppm — under a heading that also claimed USP. The USP monograph is stricter on both.
A sheet with the wrong heading is worse than no sheet. It invites you to file a European specification as USP compliance.
Where 7-KLCA sits in the pharmacopoeia — as impurity F of ursodeoxycholic acid
The ursodeoxycholic acid monograph (Ph. Eur. 1275) defines nine related substances, lettered A to I. Seven are governed by the general acceptance criterion for unspecified impurities. Only two — A and C — are singled out as specified impurities with limits of their own. 7-KLCA is the sixth letter.
| Letter | Defined as | Common name | Status in the monograph |
|---|---|---|---|
| A | 3α,7α-Dihydroxy-5β-cholan-24-oic acid | Chenodeoxycholic acid | Specified — limit 1.0% |
| B | 3α,7α,12α-Trihydroxy-5β-cholan-24-oic acid | Cholic acid | Other detectable impurity |
| C | 3α-Hydroxy-5β-cholan-24-oic acid | Lithocholic acid | Specified — limit 0.1% (TLC) |
| D | 3α,7β,12α-Trihydroxy-5β-cholan-24-oic acid | Ursocholic acid | Other detectable impurity |
| E | 3α,12α-Dihydroxy-5β-cholan-24-oic acid | Deoxycholic acid | Other detectable impurity |
| F | 3α-Hydroxy-7-oxo-5β-cholan-24-oic acid | 7-Ketolithocholic acid (7-KLCA) | Other detectable impurity |
| G | Methyl 3α,7β-dihydroxy-5β-cholan-24-oate | Methyl ursodeoxycholate | Other detectable impurity |
| H | 3β,7β-Dihydroxy-5β-cholan-24-oic acid | — | Other detectable impurity |
| I | 5β-Cholane-3α,7β,24-triol | — | Other detectable impurity |
Two points in this table carry commercial weight.
Impurity F is not a specified impurity. It has no limit of its own; it is covered by the general criterion for unspecified impurities. And the letters A to I have stayed stable across editions, so a reference to "impurity F" holds up across years of documentation and audit correspondence. The designations originate with the monograph maintained by the European Directorate for the Quality of Medicines & HealthCare.
The limit that actually applies to 7-KLCA in ursodeoxycholic acid
Inside ursodeoxycholic acid, 7-KLCA falls under the general acceptance criterion for unspecified impurities: not more than 0.10 per cent per impurity, inside a total related-substances ceiling of 1.5 per cent, above a disregard limit of 0.05 per cent. The two specified impurities are unrelated to it — impurity A, chenodeoxycholic acid, at 1.0 per cent, and impurity C, lithocholic acid, tested separately by thin-layer chromatography at 0.1 per cent.
Here is the practical consequence, and it is the single most misread point in this material.
A certificate that reports "impurity F: not detected" is making a statement about the method, not about the substance. Whether a peak could have been seen depends on the detection mode and the reporting threshold applied. Two suppliers can issue honest, non-detect certificates for the same batch using different methods, and the two documents mean different things.
There is no standalone monograph — what that changes for a specification
Because 7-KLCA is not monographed in its own right, several things follow directly.
- You cannot describe it as "Ph. Eur. grade". The phrase has no defined meaning for this substance. A supplier using it is either describing an internal standard loosely or is unaware of the distinction.
- No CEP can be issued for it. Certificates of suitability attach to substances for which a pharmacopoeial monograph exists. Where a regulatory filing covers the intermediate, that is a different instrument — ask what the supplier actually holds rather than what they might apply for.
- Acceptance criteria come from the supplier's in-house specification, which moves the burden of verification substantially onto you.
The figures on commercial sheets are therefore commercial choices, not compendial requirements. Typical sheets quote an assay floor by liquid chromatography, an appearance and identity description, and limits on volatiles, residue, and total impurities. The numbers vary between suppliers and none trace back to a pharmacopoeial source. Residual solvents, where they are controlled at all, sit under the ICH Q3C framework. The same holds elsewhere: the United States Pharmacopeia also monographs ursodeoxycholic acid as a substance and does not monograph this intermediate.
Treat those figures as the start of a negotiation, not as a standard. The right question is not "does this meet the specification?" It is "whose specification, and on what basis was each limit set?"
Why 7-KLCA matters in the supply chain
7-KLCA is not a minor curiosity. It is the pivotal intermediate in one of the principal manufacturing routes to ursodeoxycholic acid. Chenodeoxycholic acid is selectively oxidised at the 7-position to give the 7-oxo compound — this substance — which is then stereoselectively reduced to the 7β configuration to yield ursodeoxycholic acid.
That positioning explains why it turns up as impurity F in the finished material. Any incomplete reduction leaves the ketone behind. The intermediate and the impurity are the same molecule seen from two directions, which is exactly why buyers have to be explicit about which role they are purchasing for:
- As a purchased intermediate, you are buying an input to a synthesis and you care about assay, identity, and the impurities that will carry through the reaction.
- As a residual limit in ursodeoxycholic acid, you are enforcing a ceiling on something you never intended to buy.
Suppliers also list it as a precursor in the manufacture of other bile-acid derivatives. If you are evaluating it for a route not described here, ask for the route-relevant specification rather than a generic sheet.
JAN Bio supplies 7-ketolithocholic acid as a bile-acid intermediate alongside the upstream chenodeoxycholic acid and the downstream ursodeoxycholic acid.
What the official method can and cannot tell you
The pharmacopoeial related-substances test for ursodeoxycholic acid uses liquid chromatography with refractometric detection. That choice is forced by the chemistry: bile acids lack a chromophore, so ultraviolet detection at conventional wavelengths is weak. Refractive index detection is comparatively insensitive, and the published method cannot resolve all nine related substances in a single run — the monograph handles this by identifying two impurities through relative retention and by testing impurity C separately.
For a buyer the conclusion is specific: the absence of a reported impurity F peak is bounded by the capability of the method used. Do not compare impurity results across suppliers without comparing the methods that produced them. A number is only interpretable next to the technique and the reporting threshold applied to that batch. Method development in this field has been moving toward alternatives such as charged aerosol detection precisely because the pharmacopoeial approach cannot separate all nine related substances in one run — a limitation set out in published method work on the nine related substances of ursodeoxycholic acid.
A six-step checklist before you approve a batch
- Match the identity line to your order. Reject a certificate that carries only a trade name. Require the systematic name, CAS 4651-67-6, and the molecular formula C24H38O4 on the same page.
- State the role explicitly. Confirm in writing whether the material is bought as a synthesis input or controlled as a residual impurity in another product. The acceptance criteria follow from that answer.
- Ask for the method behind every impurity number. Detection mode and reporting threshold at minimum. A purity figure without a method is not verifiable.
- Request the actual spectroscopic evidence for identity, not a summary statement, and check it against the structure you ordered.
- Insist on a batch-specific certificate. Check the batch number, the manufacturing and retest dates, and that the residual-solvent panel follows ICH Q3C. A template with the batch field left as a placeholder is not evidence.
- Reconcile the label against the certificate. Storage condition, retest date and pack size should agree. Where the material is animal-derived, the sourcing statement has to line up with the rest of the documentation.
Frequently asked questions
Is there a Ph. Eur. monograph for 7-ketolithocholic acid?
No. No pharmacopoeia establishes a monograph for 7-KLCA as a substance in its own right. It is defined in pharmacopoeial text only as a related substance of ursodeoxycholic acid.
What is 7-KLCA called in the European Pharmacopoeia?
Impurity F of the ursodeoxycholic acid monograph, defined as 3α-hydroxy-7-oxo-5β-cholan-24-oic acid.
What limit applies to 7-KLCA in ursodeoxycholic acid?
It falls under the general limit for unspecified impurities, 0.10 per cent per impurity, within a total related-substances limit of 1.5 per cent and a disregard limit of 0.05 per cent. It has no individual limit of its own.
Is 7-ketolithocholic acid the same as 7-keto-chenodeoxycholic acid?
Yes, structurally. The two names describe one molecule, because chenodeoxycholic acid and lithocholic acid differ only at C7. Documentation may use either, which is why the CAS number should be checked rather than the name alone.
Does JAN Bio hold a CEP or a DMF for 7-KLCA?
No. JAN Bio is a supply-chain partner for bile-acid raw materials, not a manufacturing site, and does not hold pharmacopoeial certificates. A CEP cannot in any case be issued for a substance without a monograph. What we provide with each batch is a certificate of analysis, and we will supply safety data, residue-solvent information, and traceability documentation on request. Where a filing or certification exists, it sits with the manufacturing site, and we will tell you plainly which documents we can obtain and which we cannot.
What purity should I specify if there is no compendial grade?
Specify by function. For a synthesis input, what matters is what survives into your reaction — assay, the related bile acids that carry through, residual solvents, and physical form. Ask the supplier to justify each limit against your process rather than accepting a catalogue sheet. Where you need a documented limit and no monograph exists, that limit has to be agreed contractually.
Summary
7-KLCA occupies an unusual position. It is a commercially traded intermediate with no monograph of its own and, simultaneously, a defined impurity of a monographed substance. Buyers who collapse those two roles into one specification sheet end up with acceptance criteria that fit neither use.
Three facts to carry forward. It is impurity F of ursodeoxycholic acid, defined as 3α-hydroxy-7-oxo-5β-cholan-24-oic acid, CAS 4651-67-6. As a residual impurity it is limited at 0.10 per cent under the unspecified-impurity criterion. As a purchased intermediate it is governed by the supplier's in-house specification, so the method behind every number matters as much as the number itself.
Send us the specification you are working to and the quantity you need. We will come back with the parameters we can commit to, the documentation package we can supply with the batch, and the points where a document is not available — stated plainly rather than left ambiguous. Use our quotation request page, or contact us directly.
Disclaimer. This article is published for technical and procurement reference by JAN Bio and describes pharmacopoeial definitions and analytical practice. It contains no therapeutic, clinical, or dosing information and makes no claim about the use of any substance in the diagnosis, treatment, or prevention of disease. Pharmacopoeial limits and impurity designations are quoted from the pharmacopoeial monograph text and should be verified against the current edition applicable to your market. Specifications described as typical are commercial values published by suppliers and are not compendial requirements. Buyers should confirm all acceptance criteria against their own regulatory obligations and their supplier's batch documentation.