Compound

L-leucine

The L-enantiomer of leucine, taken as free crystalline leucine. SIX BOUNDARIES, and they matter more here than for any subject enrolled so far: of 62 live corpus papers, fifteen dose isolated leucine in humans. Most of this literature is about something that merely shares the word. (1) THE ACYL AND PEPTIDE DERIVATIVES ARE SEPARATE COMPOUNDS, AND HERE THEY ARE A DRUG PROGRAMME RATHER THAN A SUPPLEMENT. N-acetyl-L-leucine (CHEBI:58270) has its own node, and six corpus papers are its randomised trials in Niemann-Pick disease type C, ataxia-telangiectasia and acute vertigo, appearing as acetylleucine, levacetylleucine, NALL and IB1001. Dileucine and creatyl-L-leucine are likewise different molecules with different absorption, and one corpus trial exists precisely to report that dileucine did something free leucine did not. A trial dosing any of them is subject_species_mismatch, named in dosed_subject. This is more dangerous than the usual species split: those trials are large, placebo-controlled and positive, so a claim lifted from one enters at a high grade under a subject that was never given. (2) LEUCINE IS ALSO THE NAME OF A PROTEIN STRUCTURAL MOTIF. Leucine zipper, leucine-rich repeat and leucine-rich glioma-inactivated protein are features of polypeptides, not the free amino acid, and nothing is administered in those papers at all. The ingestion term retires most of them. Where one is still in front of you, decline it as other and say the word names a motif. (3) LEUCINE-ENRICHED IS THE LARGEST CLASS AND IT IS USUALLY NOT LEUCINE. Nineteen live papers give leucine inside something else: leucine-enriched whey, leucine-rich protein, leucine-enriched essential amino acids, high-leucine branched-chain amino acids, or an oral nutritional supplement also carrying omega-3, vitamin D, arginine, olive oil or probiotics. THE TEST IS THE COMPARATOR, NEVER THE NAME. Where both arms receive the same protein or amino-acid base and only the leucine differs — free leucine added to a balanced EAA mixture, a leucine-enriched protein against an isonitrogenous one — the base is balanced background, the contrast isolates leucine, and the claim is real: extract it and record the base in population. Where the treatment arm gets leucine plus a protein or nutrient the comparator lacks, the estimate belongs to neither alone: decline combination_exposure and name the split in co_exposure. Branched-chain amino acid products are the strict case, because L-isoleucine (CHEBI:17191) and L-valine (CHEBI:16414) are their own nodes — a BCAA arm against placebo is three interventions, and two of them are not this one. (4) HMB IS WHAT LEUCINE BECOMES, NOT WHAT LEUCINE IS, AND NO NODE HOLDS IT. Beta-hydroxy-beta-methylbutyrate is a downstream metabolite sold and trialled separately. There is no HMB node, so an HMB paper takes no claim anywhere; no_outcome_node does not apply, because the gap is in the subject rather than the endpoint. Decline subject_species_mismatch with HMB in dosed_subject. Its pooled trials report nulls, so mis-assigning one would put a false negative on leucine at meta-analysis weight. (5) LEUCINE IS A FORMULATION INGREDIENT OF A DENTAL CARIES GEL. Three papers compare Carisolv or BRIX3000 against rotary drilling for chemomechanical caries removal. Carisolv carries leucine, lysine and glutamic acid alongside sodium hypochlorite, and the amino acids are there to make the hypochlorite selective for degraded collagen. The endpoint is how completely a dentist removes caries. Nothing about leucine is being tested and no new outcome node would make such a paper extractable: reagent_not_exposure, with the procedure in co_exposure. (6) OBSERVED INTAKE IS ADMISSIBLE, BUT NOT AT THE TIER THE PAPER ADVERTISES. A prospective cohort relating habitual leucine intake to an outcome is a real exposure and the schema holds it at tier cohort. The trap in this corpus is that its four intake papers are SECONDARY ANALYSES OF RANDOMISED TRIALS THAT RANDOMISED SOMETHING ELSE — nutritional support in one, a cardioprotective diet in another. Nobody was assigned to leucine, so the design is observational however the parent trial is labelled: never carry the parent trial's tier onto a leucine claim. State in extraction_note that the exposure was estimated rather than assigned, and how. Measuring leucine in plasma remains subject_is_the_outcome, because no outcome node holds it.