Compound Monograph
Frangulin B
Frangulin B is an emodin monoglycoside (emodin-6-O-β-D-apioside) of alder buckthorn bark — the apiose analogue of frangulin A. It is one of the anthraquinone glycosides behind buckthorn's stimulant-laxative action, working as a prodrug that colonic bacteria convert to emodin. It has essentially no isolate-specific research; it is studied within the total buckthorn glycosides and used mainly as an HPLC marker, and it sits inside the hydroxyanthracene-derivative class restricted by the EU on genotoxicity grounds.
Sources · 2
Where Does It Come From?
Frangulin B is a naturally occurring anthraquinone glycoside (emodin monoglycoside; hydroxyanthracene derivative), found in Alder buckthorn and 1 other source. It is flagged as moderately toxic.
Concentration
Content by Source
Concentrations not reported. No percent-dry-weight or mg/g figures have been published for this compound in its source plants.
Frangulin B at a Glance
Frangulin B is an anthraquinone monoglycoside of alder buckthorn (Frangula alnus, syn. Rhamnus frangula) bark — chemically emodin-6-O-β-D-apioside, a single apiose sugar attached to the anthraquinone emodin. It is the near-twin of frangulin A (emodin-6-O-rhamnoside): same aglycone, same attachment point, a different sugar. Together with the larger diglycosides glucofrangulin A and B, the frangulins make up the anthraquinone-glycoside fraction that gives buckthorn bark its long use as a stimulant laxative.
Like the other buckthorn glycosides, frangulin B is best understood as a prodrug. It resists breakdown in the stomach and small intestine, reaches the colon largely intact, and is there cleaved by resident bacteria to free emodin (and reduced anthrone forms), which stimulate colonic motility and secretion 3,
The honest headline is that frangulin B has essentially no isolate-specific evidence. It is quantified and studied within the total buckthorn glycosides — most often as an HPLC marker for bark quality 1Reference 1Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLCView study → — rather than isolated and tested on its own. What can be said about its pharmacology and safety is inferred from the buckthorn glycoside class and from its aglycone emodin, which carries a genotoxicity signal and sits inside the hydroxyanthracene-derivative group the EU restricts in food 4,
Frangulin B vs. Frangulin A
The two frangulins are the point of confusion worth settling first: they differ only in one sugar.
- Frangulin A is emodin-6-O-α-L-rhamnoside — emodin carrying a rhamnose.
- Frangulin B is emodin-6-O-β-D-apioside — the same emodin, at the same 6-O position, carrying an apiose instead 1Reference 1Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLCView study →.
Both are emodin monoglycosides; both occur in alder buckthorn bark alongside the corresponding diglycosides, glucofrangulin A (emodin-6-O-rhamnosyl-8-O-glucoside) and glucofrangulin B (emodin-6-O-apiosyl-8-O-glucoside), which carry an extra glucose at the 8-position 1Reference 1Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLCView study →. The apiose/rhamnose split runs straight through the pair: frangulin A ↔ glucofrangulin A share the rhamnose; frangulin B ↔ glucofrangulin B share the apiose.
The practical consequence is that the two frangulins are quantified together and reasoned about together. Validated HPLC/UHPLC methods for buckthorn bark report frangulins A and B (and glucofrangulins A and B) as a set 1Reference 1Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLCView study →; the European Pharmacopoeia standardises the drug on glucofrangulins (expressed as glucofrangulin A), not on frangulin B individually. There is no body of evidence separating frangulin B’s activity from frangulin A’s, or from the buckthorn glycoside fraction as a whole — anything attributed to “frangulin B” here is really a property of the shared emodin core and the class it belongs to. This page states that collective basis rather than inventing an isolate profile.
What It's Used For
There is no meaningful isolate literature to summarise. Frangulin B’s pharmacology is the buckthorn anthraquinone-glycoside class effect, funnelled through its aglycone emodin after colonic bacterial cleavage.
Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. Both rows below rest on class/plant data, not on isolated frangulin B — read the per-row basis.
The only genuine, long-established use — and it belongs to the aged bark and the glycoside class, not to frangulin B specifically. Buckthorn’s anthraquinone glycosides survive the upper gut and are cleaved by colonic bacteria to free emodin and reduced anthrones, which inhibit colonic water/sodium reabsorption, raise luminal water (via aquaporin modulation) and stimulate the myenteric plexus, producing propulsive motility roughly 6–8 hours after intake 3,
Frangulin B is one contributor to this pooled glycoside load; its apiose sugar is cleaved to yield the same emodin as its rhamnoside twin.
Gap: frangulin B has never been dosed or tested as an isolate for laxation — the effect is documented for whole bark standardised on glucofrangulins, so frangulin B’s individual contribution is unquantified 1,
Alder buckthorn bark extracts show in-vitro antibacterial and antioxidant activity — e.g. ethanolic extracts inhibiting environmental and some pathogenic bacteria while sparing a probiotic Lactobacillus strain — but the activity is attributed to the extract’s dominant emodin/frangulin and phenolic content as a whole, with glucofrangulin measured only at ~0.12–0.34% of the extracts 2Reference 2Extracts from Frangula alnus Mill. and their effects on environmental and probiotic bacteriaView study →. Frangulin B is present but not tested as the isolate.
Gap: no assay isolates frangulin B’s own antibacterial/antioxidant contribution; these are whole-extract, in-vitro findings with no human relevance 2Reference 2Extracts from Frangula alnus Mill. and their effects on environmental and probiotic bacteriaView study →.
Mechanisms
| Target / pathway | Effect | Relevant to |
|---|---|---|
| Colonic bacterial β-glycosidases | cleave the 6-O-apioside → free emodin and reduced anthrone (the active species) | laxative activation (prodrug step) |
| Colonic Na⁺/K⁺-ATPase & aquaporins (via emodin) | ↓ water/sodium reabsorption; ↑ luminal water (AQP modulation) → softer, bulkier stool | stimulant-laxative effect |
| Myenteric plexus (via the anthrone) | stimulates propulsive colonic motility | stimulant-laxative effect |
| DNA / genotoxic endpoints (via emodin/aloe-emodin) | class genotoxicity signal in vitro (and in vivo for aloe-emodin) | toxicity / regulatory restriction |
The load-bearing point is the first two rows: frangulin B does essentially nothing until colonic bacteria strip its sugar to release emodin — the same colon-delivered anthraquinone that produces both the laxation and the safety concern.
Pharmacokinetics
No dedicated pharmacokinetic study of frangulin B exists; its kinetics are inferred from the buckthorn glycoside class. As a polar O-glycoside, frangulin B is poorly absorbed from the upper gastrointestinal tract and resists gastric and small-intestinal hydrolysis, so most reaches the colon intact, where bacterial β-glycosidases release emodin (and its anthrone) locally 3,
Clinical Trials
There are no clinical trials of isolated frangulin B, and none are planned. Its human “evidence” is the traditional-use record of aged alder buckthorn bark as a short-term stimulant laxative, recognised by the EMA on the basis of long-standing use rather than modern isolate trials 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →. The active contemporary literature around the molecule is analytical (HPLC quantification/quality control) and toxicological/regulatory (the hydroxyanthracene-derivative class), not therapeutic 1,
| Completed | Planned | Terminated | Preclinical |
|---|---|---|---|
| —(traditional buckthorn-bark use only; no isolate efficacy trials) | — | — | Laxative mechanism (class/emodin); antibacterial/antioxidant extract work; analytical/quality-control methods |
Last checked: July 2026.
Isolate vs. Plant Studies
This molecule sits at the far plant-only end of the spectrum. All of the usable evidence is for whole alder buckthorn bark or for the anthraquinone-glycoside class — the traditional laxative record, the HPLC quantification, the extract antibacterial/antioxidant assays 1,
Prevalence in Nature
Frangulin B is a bark constituent of buckthorns (Frangula / Rhamnus, Rhamnaceae). Its principal documented source is alder buckthorn (Frangula alnus, syn. Rhamnus frangula) bark, where it occurs as a minor monoglycoside alongside frangulin A and the more abundant diglycosides glucofrangulin A and B; related anthraquinones such as chrysophanol, physcion, aloe-emodin and emodin itself appear in the same bark 1,
A quality point defines the material: fresh buckthorn bark is unsafe to use. Fresh bark carries the anthraquinones in their reduced anthrone/anthranol forms, which are harsh gastric irritants that provoke violent cramping and vomiting; the bark must therefore be aged for at least a year, or heat-treated (dried and heated ~2 h at 100 °C), so the anthrones oxidise to the milder glycosides — including the frangulins and glucofrangulins — before use 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →. The European Pharmacopoeia standardises the aged bark on glucofrangulins (minimum 7.0%, expressed as glucofrangulin A); frangulin B’s individual level is low and not routinely tabulated (see this compound’s gaps tracker).
Major Natural Sources
| Source (botanical) | Part | Notes on frangulin B |
|---|---|---|
| Alder buckthorn (Frangula alnus / Rhamnus frangula) | Aged bark | Principal source; minor monoglycoside alongside frangulin A and glucofrangulins A/B; bark standardised on glucofrangulins, not frangulin B 1, |
| Other Frangula / Rhamnus spp. (e.g. Frangula rupestris) | Bark | Reported among the anthraquinone glycosides of related buckthorn barks 2Reference 2Extracts from Frangula alnus Mill. and their effects on environmental and probiotic bacteriaView study → |
No comparable dry-weight figure for frangulin B specifically is established across sources — quantification in the literature is of the glucofrangulins/total glycosides, not the individual frangulin B (see gaps tracker).
Discovery & Synthesis
Frangulin B was characterised as part of the anthraquinone chemistry of Frangula bark: once the frangulin “glucoside” of buckthorn was resolved into distinct sugars, frangulin B was defined as the apioside counterpart of the rhamnoside frangulin A, and the corresponding diglycoside pair (glucofrangulin A/B) mapped alongside 1Reference 1Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLCView study →. A precise first-isolation date and worker for frangulin B specifically are not well documented and are not asserted here. Practically, frangulin B is obtained by extraction from buckthorn bark and handled as an analytical reference standard for HPLC quality control 1Reference 1Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLCView study →; there is no established total synthesis in routine use — the molecule is more readily isolated from its natural source than built. Its close kinship to emodin (the frangulins are simply emodin 6-O-glycosides) means most of its “synthesis” interest is as a glycosylation product of the emodin aglycone.
Patents: not yet researched.
Toxicity & Safety
Frangulin B carries a moderate flag — heavier than an ordinary plant glycoside — because it is a hydroxyanthracene-derivative prodrug that delivers the genotoxic-flagged anthraquinone emodin to the colon. The flag stops short of a genotoxin/carcinogen badge because the direct genotoxicity/carcinogenicity data are for emodin, aloe-emodin and aloe whole-leaf extract, not for pure frangulin B, which has not been individually tested; but its class membership and its emodin-releasing chemistry are why it is treated as a genuine concern rather than a benign glycoside 4,
Genotoxicity & the class restriction. EFSA concluded that hydroxyanthracene derivatives should be regarded as genotoxic and carcinogenic unless shown otherwise, that emodin and aloe-emodin are genotoxic in vitro (aloe-emodin also in vivo), and that no safe intake could be set 4Reference 4Safety of hydroxyanthracene derivatives for use in foodView study →. On that basis Commission Regulation (EU) 2021/468 restricted aloe-emodin, emodin and danthron (and preparations containing them) in food to trace levels 6Reference 6Amending Annex III to Regulation (EC) No 1925/2006 as regards botanical species containing hydroxyanthracene derivatives (aloe-emodin, emodin, danthron)View study →. Frangulin B is a colon-delivered emodin prodrug and falls squarely within the class the restriction targets.
Stimulant-laxative harms (class). As part of an anthranoid laxative, chronic or high use can cause cramping, fluid and electrolyte loss (notably potassium), and dependence/atony, plus the reversible colonic pigmentation melanosis coli; EMA restricts buckthorn bark to short-term occasional use (no more than about 1–2 weeks) after gentler measures fail, and warns against use in undiagnosed abdominal pain, intestinal obstruction or inflammatory bowel conditions 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →. Fresh (un-aged) bark is an outright gastric irritant that causes violent vomiting — hence the aged-bark/heat-treatment requirement 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →.
Pregnancy & lactation (prose only). Stimulant anthranoid laxatives are conventionally cautioned in pregnancy and breastfeeding — the EMA does not recommend buckthorn-bark use in these groups given the theoretical uterine-stimulant and fluid/electrolyte concerns and possible excretion of active metabolites in milk, layered on top of the class genotoxicity signal 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →. Pregnancy/lactation decisions belong to the herb or product page where intake is actually decided, not to this molecule page — no isolate-specific verdict is issued here.
- Little intact frangulin B is systemically absorbed. Its polar O-glycoside structure keeps it in the gut lumen until colonic bacteria act on it; the freed emodin is itself poorly bioavailable 3Reference 3AnimalThe laxative effect of emodin is attributable to increased aquaporin 3 expression in the colon of mice and HT-29 cellsView study →.
- Hydroxyanthracene-derivative genotoxicity concern. The class is treated as genotoxic/carcinogenic-until-proven-otherwise; its aglycone emodin (and relative aloe-emodin) are genotoxic, and the EU restricts these substances in food 4,
6Reference 4Safety of hydroxyanthracene derivatives for use in foodView study →Reference 6Amending Annex III to Regulation (EC) No 1925/2006 as regards botanical species containing hydroxyanthracene derivatives (aloe-emodin, emodin, danthron)View study → . - Fresh bark is unsafe. Un-aged buckthorn bark causes violent cramping and vomiting; the bark must be aged ≥1 year or heat-treated before use 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →.
- Stimulant-laxative harms. Short-term use only (≈1–2 weeks); cramping, electrolyte (potassium) loss, dependence/atony with chronic use, and melanosis coli 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →.
- Flora-dependent and unstudied as an isolate. The active emodin forms only if the right colonic bacteria are present, and frangulin B’s own safety margin has never been characterised 1,
3Reference 1Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLCView study →Reference 3AnimalThe laxative effect of emodin is attributable to increased aquaporin 3 expression in the colon of mice and HT-29 cellsView study → .
Dosage
There is no dose for frangulin B — it is never taken as an isolate. It is consumed only as one of several anthraquinone glycosides in aged alder buckthorn bark, which the EMA recognises as a traditional short-term stimulant laxative: used occasionally, for no more than about 1–2 weeks, and only when a softer stool cannot be achieved by diet or bulk-forming measures, with buckthorn preparations standardised on their glucofrangulin (hydroxyanthracene) content, not on frangulin B 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →. Fresh bark must be aged at least a year or heat-treated before any use 5Reference 5ReviewCommunity herbal monograph & assessment report on Rhamnus frangula LView study →, and the whole hydroxyanthracene-derivative class is restricted in food on genotoxicity grounds 6Reference 6Amending Annex III to Regulation (EC) No 1925/2006 as regards botanical species containing hydroxyanthracene derivatives (aloe-emodin, emodin, danthron)View study →. These are class/plant context figures, not a personal recommendation, and self-dosing isolated frangulin B is neither established nor advisable.
References
- Rosenthal I, Wolfram E, Peter S, Meier B (2014). Validated method for the analysis of frangulins A and B and glucofrangulins A and B using HPLC and UHPLC. Journal of Natural Products. https://pubmed.ncbi.nlm.nih.gov/24555690/
- Kledecka A, Siejak P, Pratap-Singh A, Kowalczewski PŁ, Fathordoobady F, Jarzębski M, Smułek W (2022). Extracts from Frangula alnus Mill. and their effects on environmental and probiotic bacteria. Plants (Basel). https://pubmed.ncbi.nlm.nih.gov/36297744/
- Zheng YF, Liu CF, Lai WF, Xiang Q, Li ZF, Wang H, Lin N (2014). The laxative effect of emodin is attributable to increased aquaporin 3 expression in the colon of mice and HT-29 cells. Fitoterapia. https://pubmed.ncbi.nlm.nih.gov/24727085/
- EFSA ANS Panel (2018). Safety of hydroxyanthracene derivatives for use in food. EFSA Journal. https://pubmed.ncbi.nlm.nih.gov/32625659/
- European Medicines Agency, Committee on Herbal Medicinal Products (HMPC). Community herbal monograph & assessment report on Rhamnus frangula L. (Frangula alnus Miller), cortex. EMA/HMPC. https://www.ema.europa.eu/en/documents/herbal-report/draft-assessment-report-rhamnus-frangula-l-cortex-revision-1_en.pdf
- Commission Regulation (EU) 2021/468 (2021). Amending Annex III to Regulation (EC) No 1925/2006 as regards botanical species containing hydroxyanthracene derivatives (aloe-emodin, emodin, danthron). Official Journal of the European Union. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32021R0468
