L-Carnitine

1 Identity

Small-molecule quaternary ammonium betaine, a zwitterion at neutral pH. Not A peptide and not peptide-adjacent by structure: it is carried in this catalog because it circulates in the same channel, principally inside compounded lipotropic injection mixtures. Endogenous in humans and present in food. It is simultaneously the active moiety of FDA-approved drug products marketed under the name levocarnitine, a lawful dietary ingredient, and an ordinary catalog fine chemical. which is commonly published and is not independently verified for this entry. and CAS 541-15-1. Levocarnitine (INN, USAN, and the name under which USP monographs are published). Obsolete name not used in this catalog: "vitamin BT".

Sequence

Not applicable: not a peptide, no residues, no sequence. The structural statement that replaces a sequence is this. A four-carbon backbone bearing a carboxylate at C1, a single stereocenter at C3 carrying a hydroxyl, and a trimethylammonium group at C4. The molecule has exactly one stereocenter and the article is the (R) enantiomer. The (S) enantiomer, D-carnitine, has the identical formula and the identical mass to every decimal place and is separated only by a chiral method or by optical rotation. Because the carboxylate and the quaternary ammonium are both permanently charged over the ordinary pH range, the free compound exists as an internal salt rather than as a neutral molecule; that is why it is written as an inner salt and why it is exceptionally hygroscopic.

Molecular formula

C7H15NO3 (free inner salt / zwitterion). Hydrochloride C7H16ClNO3. L-tartrate, 2 carnitine to 1 L-tartaric acid, C18H36N2O12, equivalently 2 x C7H15NO3 . C4H6O6, CAS 36687-82-8 commonly published. Acetyl-L-carnitine C9H17NO4; acetyl-L-carnitine hydrochloride C9H18ClNO4. Propionyl-L-carnitine C11H21NO4; its hydrochloride C11H22ClNO4. Biosynthetic precursor gamma-butyrobetaine C7H15NO2; dehydration degradant crotonobetaine C7H13NO2.

Average mass

161.201 Da (C7H15NO3), on IUPAC 2021 abridged conventional atomic weights; listings commonly print 161.20. Related articles, from the formulas above: hydrochloride 197.66; L-carnitine L-tartrate (2:1) 472.49, of which 31.8 percent of the gross weight is tartrate, so a 1,000 mg fill of the tartrate contains about 682 mg of carnitine; acetyl-L-carnitine 203.24; acetyl-L-carnitine hydrochloride 239.70; propionyl-L-carnitine 231.29; propionyl-L-carnitine hydrochloride 267.75; gamma-butyrobetaine 145.20; crotonobetaine 143.19.

Monoisotopic mass

161.10519 Da neutral (C7H15NO3). Observed in positive-mode ESI as [M+H]+ 162.11247; the intact zwitterion also gives a cation at m/z 162.1125 without adduct chemistry, and the diagnostic product ion at m/z 85.0284 (C4H5O2+) and the trimethylamine-related loss at 59.0735 are what a carnitine method actually keys on. Hydrochloride 197.08187 as the neutral ion pair; acetyl-L-carnitine 203.11576, [M+H]+ 204.12304; propionyl-L-carnitine 231.14706, [M+H]+ 232.15434.

Salt / variant note

The stereocenter is the article. (1) D-carnitine, the (S) enantiomer: formula C7H15NO3, average 161.20, monoisotopic 161.10519, identical to the target to every decimal place, identical amino-acid-analysis-equivalent composition, identical infrared spectrum in solution, and separable only by a chiral method or by optical rotation. No mass measurement of any accuracy distinguishes it. (2) DL-carnitine, the racemate, CAS 406-76-8, same formula and mass again; a 50:50 racemate sold as "carnitine" delivers half the specified enantiomer and no mass spectrometer will report anything unusual. (3) L-carnitine L-tartrate (2:1), C18H36N2O12, 472.49 / 472.22682, 31.8 percent tartrate by mass, and the form in which bulk material is most often traded because the free inner salt is deliquescent. A gross fill weight of the tartrate quoted as carnitine content overstates it by more than half again. (4) L-carnitine hydrochloride C7H16ClNO3, 197.66 / 197.08187, 17.9 percent chloride by mass. (5) Acetyl-L-carnitine C9H17NO4, 203.24 / 203.11576, 42.04 Da heavier; its hydrochloride C9H18ClNO4, 239.70. (6) Propionyl-L-carnitine C11H21NO4, 231.29 / 231.14706, 70.09 Da heavier; its hydrochloride 267.75. (7) Glycine propionyl-L-carnitine, a co-formulated article rather than a single molecule, and not specifiable by one formula. (8) gamma-Butyrobetaine C7H15NO2, 145.20 / 145.11028, the biosynthetic precursor, exactly 15.99 Da lighter, that is, one oxygen, and a plausible process residue. (9) Crotonobetaine C7H13NO2, 143.19 / 143.09463, the dehydration product, 18.02 Da lighter than the target on average mass. (10) Trimethylamine, the volatile decomposition product responsible for the characteristic odor of a degraded lot, and an organoleptic red flag that precedes any instrumental result. Because the enantiomer and the racemate are isobaric with the article at any resolution, chiral purity and optical rotation are the controlling release tests here, and a UV-only purity number is not accepted as identity on a small molecule with one stereocenter and no chromophore.

2 Class & testing panel

Form

Single article

Testing panel

P6 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Published literature exists and is very large and very old by the standards of this catalog; the constraint on this record is not evidence. What exists, by study type. Primary isolation and structural chemistry dating to 1905 and the assignment of the (R) configuration in the mid-twentieth century. A substantial biochemistry literature on carnitine acyltransferases and the carnitine shuttle, in which the compound is a standard reagent and an assay substrate rather than the subject of an intervention. Human interventional literature: multiple randomized controlled trials and several Cochrane and Cochrane-style systematic reviews and meta-analyses across cardiology, nephrology and metabolic medicine, in numbers on the order of hundreds of registered studies on ClinicalTrials.gov under the levocarnitine and L-carnitine terms. Regulatory documents: FDA-approved labeling exists for levocarnitine drug products in oral and injectable routes, including approved generics, and USP-NF carries monographs for the drug substance and for three dosage forms. Analytical literature: validated LC-MS/MS methods for free and acylcarnitines in plasma and dried blood spots are standard in newborn-screening laboratories, and chiral separation methods for the D and L enantiomers are published and routine.

4 Storage & specification

Storage

White to off-white crystalline or lyophilized powder in a screw-cap amber borosilicate or HDPE container with a PTFE-lined closure, non-sterile, with no sterility claim. The handling fact that governs this record is deliquescence: the free inner salt takes up atmospheric water rapidly and will liquefy on an open bench in a humid room, which is precisely why the tartrate and hydrochloride salts exist and why bulk material is commonly traded as the tartrate. Store tightly closed and desiccated, with a desiccant sachet in the secondary pack, at 2 to 8 degrees C for routine holding or at -20 degrees C plus or minus 5 degrees C for long holds; protect from light. Containers are equilibrated to ambient temperature before opening so that moisture does not condense onto cold solid, the container is closed immediately after weighing, and Karl Fischer water is re-measured on any container that has been opened more than three times. Aqueous solutions are prepared fresh, held cold and aliquoted single-use.

Shelf life

Provisional retest interval 36 months from QA release for the L-tartrate salt and 24 months for the free inner salt, both at 2 to 8 degrees C, tightly closed and desiccated, stated as provisional pending the company's own stability data. The shorter interval on the free inner salt is not conservatism for its own sake: the deliquescent form has a real water-uptake pathway that the tartrate does not, and water is the vehicle for both the crotonobetaine dehydration route and any microbial excursion. Protocol ICH Q1A(R2)-style, 12 months real time with pulls at 0, 3, 6, 9 and 12 months plus 6 months accelerated at 40 degrees C / 75 percent relative humidity, with Karl Fischer water, appearance, assay, optical rotation and the individually named related substances gamma-butyrobetaine and crotonobetaine reported at every pull. Optical rotation is included in the stability panel and not only at release, because racemization, however slow, is the failure that would make the article a different product without changing its mass. Retest date printed on every container, first-expiry-first-out enforced against that date.