Nigellidine

Nigellidine at a Glance

Nigellidine is a minor alkaloid of black seed (Nigella sativa), and the reason it earns a page is structural: it is an indazole alkaloid, and the indazole ring is one of the rarest nitrogen heterocycles in the natural world ^{6,7Reference 6Pal D et al. · 2025The chemistry and biology of pyrazole and indazole alkaloidsView study →Reference 7Liu YM et al. · 2004A new alkaloid and its artificial derivative with an indazole ring from Nigella glanduliferaView study →}.

Almost every plant alkaloid you can name is built on a different core — indole, isoquinoline, pyridine, tropane, purine. Indazoles are common in synthetic medicinal chemistry, but only a handful of natural products contain the ring at all, and Nigella is the genus where most of them were found ^{6,7Reference 6Pal D et al. · 2025The chemistry and biology of pyrazole and indazole alkaloidsView study →Reference 7Liu YM et al. · 2004A new alkaloid and its artificial derivative with an indazole ring from Nigella glanduliferaView study →}. Nigellidine and its companion nigellicine are therefore genuine chemotaxonomic signatures of the seed.

What nigellidine is not is the reason black seed works. The herb’s evidence rests on its quinone fraction — thymoquinone, thymohydroquinone and the volatile oil around them — while the alkaloids are a small side-group with almost no isolate pharmacology of their own ^{4,9Reference 4Botnick I et al. · 2012Distribution of primary and specialized metabolites in Nigella sativa seeds, a spice with vast traditional and historical usesView study →Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}. Nigellidine’s modern literature is dominated by molecular-docking papers from the COVID-19 period, which are computer predictions, not measured activity. This page treats them as such.

An Indazole Alkaloid, and Why That Is Rare

The indazole ring is a bicyclic benzo-fused pyrazole — a benzene ring fused to a five-membered ring carrying two adjacent nitrogens. That adjacent N–N bond is the unusual part: plants build C–N bonds readily, but direct nitrogen–nitrogen bonds are uncommon in secondary metabolism, which is why indazoles are abundant in synthetic drug and agrochemical scaffolds and almost absent from natural-product catalogues ^{6Reference 6Pal D et al. · 2025The chemistry and biology of pyrazole and indazole alkaloidsView study →}.

Nigellidine specifically is a pyridazino-indazolium betaine — the indazole nucleus fused to a further nitrogen-containing ring, carrying a permanent positive charge balanced internally, with a p-hydroxyphenyl substituent. Its structural neighbour nigellicine belongs to the same pyridazinoindazolium family ^{10Reference 10Elliott EL et al. · 2005Total synthesis of nigellicine and nigeglanine hydrobromideView study →} and has been characterised specifically as a pseudo-cross-conjugated betainic alkaloid — a charge arrangement unusual enough that synthetic chemists have built model compounds to study it ^{14Reference 14Schmidt A et al. · 2003New pyrazolium-carboxylates as structural analogues of the pseudo-cross-conjugated betainic alkaloid nigellicineView study →}.

How rare is rare? When nigeglanine was reported from Nigella glandulifera in 2004, it was described as only the third natural product then known to contain an indazole nucleus — the other two being the Nigella indazoles nigellicine and nigellidine ^{7Reference 7Liu YM et al. · 2004A new alkaloid and its artificial derivative with an indazole ring from Nigella glanduliferaView study →}. The count has grown since (six indazole-type alkaloids were isolated from a single defatted N. sativa extract in 2014, two of them new ^{3Reference 3Yuan T et al. · 2014In vitroIndazole-type alkaloids from Nigella sativa seeds exhibit antihyperglycemic effects via AMPK activation in vitroView study →}), and a further indazole, 4-aminonigellidine, was described from N. glandulifera in 2017 ^{8Reference 8Guo WH et al. · 2017Three new alkaloids from the seeds of Nigella glanduliferaView study →} — but the class remains small, and it remains centred on this one genus.

There is a real chemical subtlety here too. The 2008 isolation of nigellidine-4-O-sulfite from N. sativa seed — the first sulfated indazole-type alkaloid ever reported — carried a suggestion that the sulfite ester may be the true natural product, with free nigellidine arising from hydrolysis during isolation ^{2Reference 2Ali Z et al. · 2008Nigellidine-4-O-sulfite, the first sulfated indazole-type alkaloid from the seeds of Nigella sativaView study →}. If that is right, some of what has been catalogued as “nigellidine in the seed” is partly an extraction artefact of its own conjugate.

Nigellidine vs. the Quinone Fraction

It is worth stating plainly, because supplement marketing does not: black seed’s clinical record does not belong to its alkaloids.

Nigella sativa seed is roughly 30%+ fixed oil, rich in linoleic acid, plus a small volatile oil (~0.4–0.5% of seed) built around thymoquinone, its redox partner thymohydroquinone, the polymer nigellone, and monoterpenes including p-cymene and carvacrol ^{4,9Reference 4Botnick I et al. · 2012Distribution of primary and specialized metabolites in Nigella sativa seeds, a spice with vast traditional and historical usesView study →Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}. The standard pharmacology review of the plant attributes “much of the biological activity of the seeds” to thymoquinone, and treats the alkaloids as one line item in the seed’s composition ^{9Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}.

The alkaloids are also, physically, in a different place. Metabolite mapping of the seed shows that nigellidine and nigellicine — along with the monoterpenes and quinones — are almost exclusively accumulated in the seed coat, while organic acids and amino acids sit in the inner tissues ^{4Reference 4Botnick I et al. · 2012Distribution of primary and specialized metabolites in Nigella sativa seeds, a spice with vast traditional and historical usesView study →}. That is a genuine finding about where the chemistry lives, not a claim about what it does.

The practical consequence: do not read thymoquinone’s evidence onto this molecule. Standardisation, trial data, dosing and safety for black seed all track the quinone fraction. Nigellidine is a marker.

The Docking-Study Problem

Nigellidine has an unusually distorted publication record, and anyone searching for it will run straight into it.

During the COVID-19 period, nigellidine became a favourite ligand in molecular-docking and network-pharmacology papers, which reported it binding SARS-CoV-2 main protease, NSP2, nsp3, RdRp, spike, and host targets including IL-1R, IL-6R, ACE and angiotensin receptors. The same treatment was subsequently applied to dengue protease, rabbit haemorrhagic disease virus polymerase, SIRT7, P-glycoprotein and thyroxine-binding globulin. None of these is evidence that nigellidine does anything. Docking is a geometric scoring exercise against a static protein structure; it generates hypotheses, not activity.

The scale is documented. A scoping review of alkaloids proposed for COVID-19 found that 65% of the 63 eligible studies were in-silico models, and listed nigellidine among the alkaloids that “showed higher binding energy with more than two target proteins” — a computational observation, explicitly framed as such ^{5Reference 5Gonzalez BL et al. · 2022ReviewThe naturally-derived alkaloids as a potential treatment for COVID-19: a scoping reviewView study →}.

One paper deserves specific handling because it is the most-cited nigellidine reference and looks like more than it is. Maiti and colleagues docked nigellidine against COVID-19 and cytokine-receptor proteins and ran a rat experiment — but the animals were dosed with Nigella sativa extract, not with nigellidine, so the antioxidant and hepato-renal readouts belong to the whole seed extract; the paper nonetheless concludes that “nigellidine has hepato-reno-protective / antioxidant-immunomodulatory / anti-inflammatory activities” ^{11Reference 11Maiti S et al. · 2022AnimalActive-site molecular docking of nigellidine with nucleocapsid-NSP2-MPro of COVID-19 and to human IL1R-IL6R and strong antioxidant role of Nigella sativa in experimental ratsView study →}. That conclusion outruns what was dosed. Treat it as an extract result with a docking appendix.

Nothing in the docking literature contributes to the support scores below.

What It's Used For

The honest picture is thin. Setting the docking papers aside, the wet-lab record for nigellidine as an isolate amounts to a handful of natural-product-chemistry papers, one in-vitro metabolic assay on a derivative, and reviews that name it without testing it.

Evidence by IndicationStrength of support · Beta

Support is an experimental score — weighted by study type (human > animal > in vitro) and volume. A beta, not a validated metric. Read the shape here carefully: the best-supported row is an analytical role, every therapeutic row is low, and no molecular-docking study contributed to any score.

01Chemotaxonomic and Analytical MarkerShaky30%Repeated isolation and structural characterisation; mapped seed-coat localisation ^{1,2,3,4Reference 1Atta-ur-Rahman et al. · 1995Nigellidine — a new indazole alkaloid from the seeds of Nigella sativaView study →Reference 2Ali Z et al. · 2008Nigellidine-4-O-sulfite, the first sulfated indazole-type alkaloid from the seeds of Nigella sativaView study →Reference 3Yuan T et al. · 2014In vitroIndazole-type alkaloids from Nigella sativa seeds exhibit antihyperglycemic effects via AMPK activation in vitroView study →Reference 4Botnick I et al. · 2012Distribution of primary and specialized metabolites in Nigella sativa seeds, a spice with vast traditional and historical usesView study →}

02AMPK Activation and Glucose Consumption In VitroShaky18%One in-vitro hepatocyte study — and the active compound was a nigellidine glycoside derivative ^{3Reference 3Yuan T et al. · 2014In vitroIndazole-type alkaloids from Nigella sativa seeds exhibit antihyperglycemic effects via AMPK activation in vitroView study →}

03Antioxidant and Anti-Inflammatory ActivityShaky12%Whole-extract animal data attributed to the alkaloid; no isolate assay ^{9,11Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →Reference 11Maiti S et al. · 2022AnimalActive-site molecular docking of nigellidine with nucleocapsid-NSP2-MPro of COVID-19 and to human IL1R-IL6R and strong antioxidant role of Nigella sativa in experimental ratsView study →}

04Antimicrobial ContributionShaky10%Named in review compound lists; the reported MICs belong to other constituents ^{13Reference 13Abbas M et al. · 2024ReviewAntimicrobial properties and therapeutic potential of bioactive compounds in Nigella sativa: a reviewView study →}

Mechanisms

The last row is the point of the table. Nigellidine’s most voluminous “mechanism” literature is computational, and none of it has been confirmed at the bench.

Pharmacokinetics

There are no pharmacokinetic data for nigellidine — absorption, oral bioavailability, distribution, metabolism, active metabolites and half-life are all uncharacterised. Two structural points are worth flagging as inference rather than measurement. First, nigellidine is a permanently charged betaine, and quaternised/charged alkaloids generally absorb poorly across the gut wall — a reason for caution about any claim built on in-vitro concentrations. Second, the natural occurrence of nigellidine-4-O-sulfite in the seed ^{2Reference 2Ali Z et al. · 2008Nigellidine-4-O-sulfite, the first sulfated indazole-type alkaloid from the seeds of Nigella sativaView study →} means the molecule arrives already partly conjugated, which further complicates any assumption about what reaches circulation. Human exposure is in any case as a trace seed-coat constituent of a culinary spice, not as a dose.

Clinical Trials

There are no clinical trials of isolated nigellidine — none completed, planned or terminated. The clinical trial record for Nigella sativa is substantial, but it belongs to the seed, the oil and thymoquinone-standardised preparations, and cannot be transferred to this molecule.

Last checked: July 2026.

Isolate vs. Plant Studies

This molecule shows the isolate-vs-plant gap in its most extreme form, and in an unusual direction.

The chemistry is isolate work and it is good. Nigellidine has been isolated, structurally elucidated by NMR, MS and X-ray, catalogued alongside its sulfite conjugate and its glycosides, and total-synthesised ^{1,2,3,12Reference 1Atta-ur-Rahman et al. · 1995Nigellidine — a new indazole alkaloid from the seeds of Nigella sativaView study →Reference 2Ali Z et al. · 2008Nigellidine-4-O-sulfite, the first sulfated indazole-type alkaloid from the seeds of Nigella sativaView study →Reference 3Yuan T et al. · 2014In vitroIndazole-type alkaloids from Nigella sativa seeds exhibit antihyperglycemic effects via AMPK activation in vitroView study →Reference 12Ye M et al. · 2013A robust protocol for Pd(II)-catalyzed C-3 arylation of (1H) indazoles and pyrazoles: total synthesis of nigellidine hydrobromideView study →}. As a chemical entity it is well defined.

The pharmacology is almost entirely plant work wearing the isolate’s name. Every antioxidant, hepatoprotective and anti-inflammatory claim made for nigellidine traces back either to whole N. sativa extract in animals ^{9,11Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →Reference 11Maiti S et al. · 2022AnimalActive-site molecular docking of nigellidine with nucleocapsid-NSP2-MPro of COVID-19 and to human IL1R-IL6R and strong antioxidant role of Nigella sativa in experimental ratsView study →} or to thymoquinone, the seed’s dominant and far better studied quinone ^{9Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}. The single exception — AMPK-mediated glucose consumption in HepG2 cells — is a true isolate result, but for a glycosylated derivative rather than for nigellidine ^{3Reference 3Yuan T et al. · 2014In vitroIndazole-type alkaloids from Nigella sativa seeds exhibit antihyperglycemic effects via AMPK activation in vitroView study →}.

And a third category exists here that most compound pages don’t need: predicted activity. The docking literature is neither isolate nor plant evidence; it is neither in vitro nor in vivo. It is a hypothesis-generation exercise, and on this molecule it substantially outweighs the real data by volume ^{5Reference 5Gonzalez BL et al. · 2022ReviewThe naturally-derived alkaloids as a potential treatment for COVID-19: a scoping reviewView study →}.

Prevalence in Nature

Nigellidine is, so far as the literature records, essentially a Nigella molecule. It was isolated from the seeds of Nigella sativa (Ranunculaceae) ^{1Reference 1Atta-ur-Rahman et al. · 1995Nigellidine — a new indazole alkaloid from the seeds of Nigella sativaView study →}, and its indazole relatives have been described from the related Nigella glandulifera — nigeglanine in 2004 ^{7Reference 7Liu YM et al. · 2004A new alkaloid and its artificial derivative with an indazole ring from Nigella glanduliferaView study →} and 4-aminonigellidine in 2017 ^{8Reference 8Guo WH et al. · 2017Three new alkaloids from the seeds of Nigella glanduliferaView study →}.

Within the seed its distribution is well mapped and quite specific: nigellidine and nigellicine are almost exclusively accumulated in the seed coat, together with the monoterpenes and quinones, while organic acids, amino acids and the bulk of the inner-tissue metabolome sit elsewhere ^{4Reference 4Botnick I et al. · 2012Distribution of primary and specialized metabolites in Nigella sativa seeds, a spice with vast traditional and historical usesView study →}. In quantitative terms it is a minor constituent — the seed’s mass is dominated by fixed oil (>30%, chiefly linoleic acid) with a small volatile fraction (~0.4–0.5%) ^{9Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}, and the alkaloids form a small group beside them. No reliable published figure for nigellidine as a percentage of the seed was located.

The wider point is the interesting one. Indazole alkaloids are rare across the whole plant kingdom ^{6Reference 6Pal D et al. · 2025The chemistry and biology of pyrazole and indazole alkaloidsView study →}, and the small natural set that exists is concentrated in this one genus ^{7Reference 7Liu YM et al. · 2004A new alkaloid and its artificial derivative with an indazole ring from Nigella glanduliferaView study →}. If you are looking for an indazole in nature, Nigella is where you look.

Discovery & Synthesis

Nigellidine was isolated in 1995 by Atta-ur-Rahman, S. Malik, S. S. Hasan and colleagues at Karachi, from the seeds of Nigella sativa, and reported in Tetrahedron Letters as “a new indazole alkaloid” ^{1Reference 1Atta-ur-Rahman et al. · 1995Nigellidine — a new indazole alkaloid from the seeds of Nigella sativaView study →} — part of the same long-running programme that had earlier described the Nigella isoquinoline alkaloids nigellimine and nigellimine N-oxide. Thirteen years later, Ali and co-workers at the University of Mississippi isolated nigellidine-4-O-sulfite from the same seed, confirmed it by NMR, MS and X-ray crystallography, and proposed that the sulfite ester may be the true natural product from which free nigellidine is generated during isolation — the first report of a naturally occurring sulfated indazole-type alkaloid ^{2Reference 2Ali Z et al. · 2008Nigellidine-4-O-sulfite, the first sulfated indazole-type alkaloid from the seeds of Nigella sativaView study →}.

First total synthesis: 2013. Ye, Edmunds, Morris, Sale, Zhang and Yu (Scripps) developed a Pd(II)/phenanthroline-catalysed direct C-3 arylation of 1H-indazoles and pyrazoles — a genuinely difficult transformation, since the indazole C-3 position is poorly reactive — and demonstrated it with the first total synthesis of nigellidine hydrobromide ^{12Reference 12Ye M et al. · 2013A robust protocol for Pd(II)-catalyzed C-3 arylation of (1H) indazoles and pyrazoles: total synthesis of nigellidine hydrobromideView study →}. The related Nigella indazoles nigellicine and nigeglanine hydrobromide had been synthesised earlier, in 2005, via a common intermediate using ortho-lithiation/acylation and direct amination of an isatin ring ^{10Reference 10Elliott EL et al. · 2005Total synthesis of nigellicine and nigeglanine hydrobromideView study →}.

Manufacture today: none. Nigellidine is not produced commercially. It is not sold as an isolated supplement, and the synthetic routes above exist as methodology demonstrations rather than as production processes. Human exposure to the molecule is via black seed itself.

Patents: not yet researched.

Toxicity & Safety

Nigellidine carries a low flag, and the reasoning behind that badge should be read as much as the badge itself.

The case for low is exposure-based rather than data-based: nigellidine is a trace seed-coat constituent of a culinary spice with a very long history of dietary use, and the seed as a whole is described in the reference pharmacology review as “characterized by a very low degree of toxicity”, with no adverse liver or kidney effects on extended dosing and only isolated reports of contact dermatitis ^{9Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}. Nothing in the literature flags nigellidine as a hazard.

The case for caution is that no isolate toxicology package exists at all. There is no acute or repeat-dose study, no genotoxicity assay, no reproductive dataset, and no pharmacokinetic characterisation for purified nigellidine. Absence of a toxicology file is not a demonstration of safety — it is an absence.

Safety at a Glance

✅ Low / no toxicity

• Trace dietary constituent of a well-tolerated spice. Black seed itself has a very low reported toxicity profile across extended animal dosing ^{9Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}.
• No isolate toxicology whatsoever. No acute, repeat-dose, genotoxicity, reproductive or pharmacokinetic data exist for purified nigellidine — the low flag is exposure-based, not measured.
• Do not read black seed’s safety or efficacy data onto this molecule. The herb’s trial record, dosing and cautions track the quinone fraction, chiefly thymoquinone ^{9Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}.
• Beware the docking literature. Nigellidine is widely proposed as an inhibitor of viral and inflammatory targets on the basis of computer modelling with no wet-lab confirmation ^{5,11Reference 5Gonzalez BL et al. · 2022ReviewThe naturally-derived alkaloids as a potential treatment for COVID-19: a scoping reviewView study →Reference 11Maiti S et al. · 2022AnimalActive-site molecular docking of nigellidine with nucleocapsid-NSP2-MPro of COVID-19 and to human IL1R-IL6R and strong antioxidant role of Nigella sativa in experimental ratsView study →}; those papers say nothing about what it does in a body.

Dosage

There is no established or studied human dose for isolated nigellidine. It has never been administered to people as an isolate, it is not sold as a supplement, and it has no defined therapeutic use — so there is no figure to report and nothing here should be read as a dosing recommendation.

Exposure happens only through black seed itself, where nigellidine is a trace seed-coat alkaloid. Dosing for the herb — ground seed or cold-pressed oil — belongs on the nigella monograph, and it is standardised, where it is standardised at all, to thymoquinone, not to the alkaloids ^{9Reference 9Ali BH · 2003Pharmacological and toxicological properties of Nigella sativaView study →}.

References

1. Atta-ur-Rahman, Malik S, Hasan SS, Choudhary MI, Ni CZ, Clardy J (1995). Nigellidine — a new indazole alkaloid from the seeds of Nigella sativa. Tetrahedron Letters 36(12):1993–1996. https://doi.org/10.1016/0040-4039(95)00210-4
2. Ali Z, Ferreira D, Carvalho P, Avery MA, Khan IA (2008). Nigellidine-4-O-sulfite, the first sulfated indazole-type alkaloid from the seeds of Nigella sativa. Journal of Natural Products. https://pubmed.ncbi.nlm.nih.gov/18471018/
3. Yuan T, Nahar P, Sharma M, et al. (2014). Indazole-type alkaloids from Nigella sativa seeds exhibit antihyperglycemic effects via AMPK activation in vitro. Journal of Natural Products. https://pubmed.ncbi.nlm.nih.gov/25299458/
4. Botnick I, Xue W, Bar E, et al. (2012). Distribution of primary and specialized metabolites in Nigella sativa seeds, a spice with vast traditional and historical uses. Molecules. https://pubmed.ncbi.nlm.nih.gov/22922285/
5. Gonzalez BL, de Oliveira NC, Ritter MR, et al. (2022). The naturally-derived alkaloids as a potential treatment for COVID-19: a scoping review. Phytotherapy Research. https://pubmed.ncbi.nlm.nih.gov/35355337/
6. Pal D, Thakur S, Takeshwar, Chourasia P, Malik U (2025). The chemistry and biology of pyrazole and indazole alkaloids. The Alkaloids: Chemistry and Biology. https://pubmed.ncbi.nlm.nih.gov/40713154/
7. Liu YM, Yang JS, Liu QH (2004). A new alkaloid and its artificial derivative with an indazole ring from Nigella glandulifera. Chemical & Pharmaceutical Bulletin. https://pubmed.ncbi.nlm.nih.gov/15056964/
8. Guo WH, Li XM, Huang SS, Yang MH, Kong LY (2017). Three new alkaloids from the seeds of Nigella glandulifera. Journal of Asian Natural Products Research. https://pubmed.ncbi.nlm.nih.gov/27256560/
9. Ali BH, Blunden G (2003). Pharmacological and toxicological properties of Nigella sativa. Phytotherapy Research. https://pubmed.ncbi.nlm.nih.gov/12722128/
10. Elliott EL, Bushell SM, Cavero M, Tolan B, Kelly TR (2005). Total synthesis of nigellicine and nigeglanine hydrobromide. Organic Letters. https://pubmed.ncbi.nlm.nih.gov/15932220/
11. Maiti S, Banerjee A, Nazmeen A, Kanwar M, Das S (2022). Active-site molecular docking of nigellidine with nucleocapsid-NSP2-MPro of COVID-19 and to human IL1R-IL6R and strong antioxidant role of Nigella sativa in experimental rats. Journal of Drug Targeting. https://pubmed.ncbi.nlm.nih.gov/32875925/
12. Ye M, Edmunds AJ, Morris JA, Sale D, Zhang Y, Yu JQ (2013). A robust protocol for Pd(II)-catalyzed C-3 arylation of (1H) indazoles and pyrazoles: total synthesis of nigellidine hydrobromide. Chemical Science. https://pubmed.ncbi.nlm.nih.gov/23691269/
13. Abbas M, Gururani MA, Ali A, et al. (2024). Antimicrobial properties and therapeutic potential of bioactive compounds in Nigella sativa: a review. Molecules. https://pubmed.ncbi.nlm.nih.gov/39459282/
14. Schmidt A, Habeck T, Kindermann MK, Nieger M (2003). New pyrazolium-carboxylates as structural analogues of the pseudo-cross-conjugated betainic alkaloid nigellicine. The Journal of Organic Chemistry. https://pubmed.ncbi.nlm.nih.gov/12868936/

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