Ibogaine Chemical Structure

Ibogaine, in one paragraph of chemistry

Ibogaine is a monoterpenoid indole alkaloid of the iboga type, isolated from the root bark of Tabernanthe iboga in 1901. Its molecular formula is C20H26N2O and its average molecular weight is 310.4 g/mol. Structurally it is an indole ring bearing a methoxy group, fused through a seven-membered bridge to an isoquinuclidine cage that carries an ethyl substituent. Chemists frequently call it 12-methoxyibogamine, because that is exactly what it is: the ibogamine skeleton plus one methoxy group. Four defined stereocentres fix its three-dimensional shape, so the formula alone does not identify it. The material used in clinical settings is usually the hydrochloride salt, a different chemical entity with a different weight.

• Molecular formula: C20H26N2O (free base) · C20H27ClN2O (hydrochloride)
• Molecular weight: 310.4 g/mol (base) · 346.9 g/mol (HCl salt)
• Monoisotopic mass: 310.204513 · protonated ion [M+H]+ at m/z 311.21
• CAS 83-74-9 · PubChem CID 197060 · ChEBI:5852 · UNII 3S814I130U
• InChIKey: HSIBGVUMFOSJPD-CFDPKNGZSA-N
• Melting point: 148 °C (CRC Handbook of Chemistry and Physics, 94th ed.)

What C20H26N2O actually says, and what it leaves out

A molecular formula is a headcount of atoms. C20H26N2O means twenty carbon atoms, twenty-six hydrogens, two nitrogens and one oxygen in a single molecule of ibogaine. Add up the average atomic masses and you get 310.4 grams per mole, the figure listed on PubChem's record for compound 197060. If you weigh out 310.4 grams of pure ibogaine free base you have, to a good approximation, one mole of it, or about 6.02 x 10^23 molecules.

Mass spectrometry works from a different number. The monoisotopic mass, calculated using the most abundant isotope of each element rather than the natural-abundance average, is 310.204513. That precision matters because it is what an instrument compares against: the protonated molecular ion [M+H]+ shows up at m/z 311.21, and a high-resolution instrument can distinguish that from other compounds that share the same nominal mass of 310.

The two nitrogens are worth pausing on, because they are what make ibogaine an alkaloid rather than simply a plant chemical. One sits in the indole ring, where it is part of an aromatic system and only weakly basic. The other sits in the isoquinuclidine cage as a tertiary amine, and that one is genuinely basic. It is the atom that accepts a proton when hydrochloric acid is added, and it is therefore the reason a hydrochloride salt exists at all.

What the formula does not tell you is which molecule you have. Tabernanthine, another alkaloid from the same root bark, is also C20H26N2O at 310.4 g/mol. So is ibogamiline. A formula, or a nominal mass, or a stated weight on a label, is not an identification. That distinction is not academic when the number is being used to calculate a dose.

An indole and a cage, joined by a bridge

The iboga alkaloids are built on a shared framework. At one end is an indole: the fused bicyclic aromatic system that also forms the core of tryptamine, serotonin and a great many plant alkaloids. At the other end is an isoquinuclidine, a rigid three-dimensional cage formally known as an azabicyclo[2.2.2]octane, carrying an ethyl group. A seven-membered ring bridges the two. That combination is the ibogamine skeleton, and every iboga-type alkaloid is a variation on it.

Ibogaine is that skeleton with a methoxy group (OCH3) on the indole's benzene ring. This is why the semisystematic name 12-methoxyibogamine keeps appearing in the literature, and why the arithmetic works out neatly: ibogamine is C19H24N2 at 280.4 g/mol, and adding a methoxy in place of a hydrogen gives C20H26N2O at 310.4.

The full systematic name is a mouthful, and it is worth reading once rather than skipping. PubChem gives it as (1R,15R,17S,18S)-17-ethyl-7-methoxy-3,13-diazapentacyclo[13.3.1.0(2,10).0(4,9).0(13,18)]nonadeca-2(10),4(9),5,7-tetraene. The stereodescriptors at the front are the important part for identity: ibogaine has four defined stereocentres, and the naturally occurring compound is the levorotatory (-) form. A synthetic route that produced the mirror image would produce a different substance with the same formula and the same mass.

The rigidity of that cage is a genuine structural feature rather than trivia. Unlike a flexible chain, the isoquinuclidine holds the indole and the amine in a fixed spatial relationship, which is what gives the iboga alkaloids a distinctive shape among indole alkaloids and why the family is studied as a scaffold in its own right.

Why 1,000 mg of the salt is not 1,000 mg of ibogaine

The most consequential number on this page is 89.5 percent

Ibogaine free base does not dissolve well in water and is awkward to handle. Adding hydrochloric acid protonates that basic tertiary amine and produces ibogaine hydrochloride, a stable crystalline salt that dissolves, stores and weighs predictably. That is why almost all clinical and research material is the hydrochloride, and why published protocols describe it that way.

The consequence is arithmetic. The chloride and the extra proton contribute about 36.5 to the molecular weight, so the ibogaine portion of the salt is 310.4 divided by 346.9, or 89.5 percent. A gram of the salt carries about 895 milligrams of ibogaine. Anyone converting between the two forms without applying that factor is off by more than ten percent before they start.

This is exactly why a milligram-per-kilogram figure quoted with no salt form attached is incomplete information rather than a dose. It is also one of the reasons that a total alkaloid extract, which is a standardised mixture of many iboga alkaloids rather than a single purified compound, cannot be substituted milligram for milligram against purified ibogaine hydrochloride. We wrote that comparison out in full in TA versus HCl.

One clarification, because the two numbers you will encounter are not answering the same question. The 89.5 percent above is pure stoichiometry: it is what the molecular weights say and nothing more. Clinical protocols generally apply a larger correction than that, because assayed material is 95 to 99 percent pure rather than 100 percent, and the purity discount stacks on top of the salt discount. A protocol conversion factor and a stoichiometric ratio are different things, and it is worth knowing which one you are reading.

None of this is a dosing instruction, and it should not be read as one. It is the reason weight-based figures found online are so often not comparable with each other, and the reason a clinical programme calculates from a known, assayed, named salt form rather than from a number someone repeated.

The molecules ibogaine is most easily confused with

Three places where the structure shows up in the clinic

The methoxy group is a metabolic handle. The liver enzyme CYP2D6 removes its methyl, converting ibogaine into noribogaine. That single structural change is why people who metabolise poorly through CYP2D6 handle the compound differently from people who do not, and it is why pharmacogenomic screening is part of a careful protocol rather than an optional extra.

The molecule blocks the hERG potassium channel. hERG carries the rapid delayed-rectifier current that repolarises heart muscle, and blocking it lengthens the QT interval on an EKG. A sufficiently prolonged QT interval can degenerate into the ventricular arrhythmia torsades de pointes. This is a real, dose-dependent property of the structure that screening and continuous monitoring manage rather than eliminate, and it is the single reason cardiac screening before any dose is not a formality.

Lipophilicity governs where it goes. Ibogaine's calculated XLogP is 3.9 with a topological polar surface area of 28.3 square angstroms, one hydrogen-bond donor and two acceptors. In plain terms it is a fat-soluble molecule that crosses the blood-brain barrier readily and distributes into tissue rather than staying in plasma, which is part of why plasma concentration and clinical effect do not track each other neatly.

We have deliberately kept efficacy off this page. What ibogaine has and has not been shown to do, in which populations, with what evidence, belongs on the compound overview and how ibogaine works. Ibogaine is investigational. It is a Schedule I controlled substance in the United States and is not approved by the FDA for any indication.

How a laboratory proves a sample is actually ibogaine

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