flucytosine

CHEBI:5100 ·resolve ·ANTIFUNGAL ·EXACT SEEDED

An organofluorine compound that is cytosine that is substituted at position 5 by a fluorine. A prodrug for the antifungal 5-fluorouracil, it is used for the treatment of systemic fungal infections. — ChEBI

Machine-generated and unreviewed. Identity, structure and cross-references come straight from ChEBI's and CARD's own data; no curator has signed off on this record yet.

Classification

nucleoside antibioticARO:3000034

Strictly broader compounds or drug classes this molecule belongs to.

Label unavailable CHEBI:37143
Label unavailable CHEBI:38337
Label unavailable CHEBI:38338
Label unavailable CHEBI:60783
pyrimidine antifungal drug CHEBI:87205
nucleoside antibiotic ARO:3000034
pyrimidine antifungal ARO:3007560

Chemical structure

Computed structure properties
Molecular formula	C4H4FN3O
Charge	0
Average mass	129.094 Da
Monoisotopic mass	129.03384 Da
Source	ChEBI
InChIKey	XRECTZIEBJDKEO-UHFFFAOYSA-N

SMILES

Nc1nc(=O)ncc1F

InChI

InChI=1S/C4H4FN3O/c5-2-1-7-4(9)8-3(2)6/h1H,(H3,6,7,8,9)

Also called

Ancotil (BRAND_NAME)— chebi
flucytosina (INN)— chebi
flucytosinum (INN)— chebi
4-amino-5-fluoropyrimidin-2(1H)-one (EXACT_SYNONYM)— chebi
5-FC (EXACT_SYNONYM)— chebi
5-Fluorocystosine (EXACT_SYNONYM)— chebi
5-Fluorocytosine (EXACT_SYNONYM)— chebi
Ancobon (TN) (EXACT_SYNONYM)— chebi

Cross-references

Identifiers for this same structure in other resources. An accession that lands on two different structures in this corpus is withheld from both rather than shown here, since it names at most one of them.

Drug registries

Identifiers that name a drug rather than a structure. One of these can cover a parent compound, its salts and its stereoisomers, which this corpus keeps as separate records, so it is not an equivalence of structure.

Patents and articles

Documents about this compound. A patent covers a class and an article covers a topic; neither identifies a structure.

Activity roles

Every antimicrobial role a source asserts for this compound — the unreduced evidence behind its antimicrobial_class.

antifungal agent CHEBI:35718
antifungal drug CHEBI:86327

Source concepts

Every upstream concept that resolved to this record. The merge is the product: this is what shows ChEBI and CARD are describing the same structure.

Upstream concepts merged into this record
Source	Native ID	Label	Minted CURIE	Version
ARO	`ARO:3007558`	5-flucytosine	`antibioticmech:aro-39cd22b2c6`	2026-08-30
ARO	`ARO:3009160`	5-fluorocytosine	`antibioticmech:aro-0e2ad8e0aa`	2026-08-30
CHEBI	`CHEBI:5100`	flucytosine	`antibioticmech:chebi-e46c25078c`	2026-08-30

Mechanism summary

Clinical status: APPROVED

Resistance mechanisms

10 source-backed resistance determinants or associations, with ARO grounding where reported. Grouped by reported mechanism type.

ANTIBIOTIC_TARGET_ALTERATION 5

ANTIBIOTIC_TARGET_ALTERATION
Determinant	ARO ID	Organism	Gene families	Evidence
Candida spp. FUR1 with mutations conferring resistance to 5-flucytosine	ARO:3007557	not organism-specific	—	ARO:3007557 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3007558 (5-flucytosine); database assertion, not a primary citation.)
Cryptococcus neoformans USX1 UDP-xylose synthase with mutations conferring resistance to 5-fluorocytosine	ARO:3009629	not organism-specific	—	ARO:3009629 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3007558 (5-flucytosine); database assertion, not a primary citation.)
Cryptococcus neoformans Ura6 uridylate kinase with mutations conferring resistance to 5-fluorocytosine	ARO:3009633	not organism-specific	—	ARO:3009633 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3009160 (5-fluorocytosine); database assertion, not a primary citation.)
Nakaseomyces glabratus Fur1 with mutations associated with resistance to 5-fluorocytosine	ARO:3009286	not organism-specific	—	ARO:3009286 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3009160 (5-fluorocytosine); database assertion, not a primary citation.)
Saccharomyces spp. FUR1 with mutations conferring resistance to 5-flucytosine	ARO:3007559	not organism-specific	—	ARO:3007559 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3007558 (5-flucytosine); database assertion, not a primary citation.)

OTHER 2

OTHER
Determinant	ARO ID	Organism	Gene families	Evidence
FUR1-associated flucytosine resistance in LL13-040-derived cohort Gene-level cohort association; not allele-specific causality or resistance of the parental strain. Not all screened derivatives carried FUR1 changes. UniProtKB:P18562 (entry 192, sequence 2; S288c, NCBITaxon:559292; locus YHR128W) is reference-only. No tested-allele protein, strain TaxID, sample/genome ID, MIC or clinical category assigned.	—	Saccharomyces cerevisiae `NCBITaxon:4932` FUR1	FUR1	PMID:37856537 (Direct 5-FC results: sec003/sec005; Figures 2 and 4C. Cohort association.) UniProtKB:P18562 (FUR1 reference identity only; release 2026_03.) Relative colony-growth area under the curve
FUR1-associated flucytosine resistance in NC-02-derived cohort Gene-level cohort association; not allele-specific causality or resistance of the parental strain. Not all screened derivatives carried FUR1 changes. UniProtKB:P18562 (entry 192, sequence 2; S288c, NCBITaxon:559292; locus YHR128W) is reference-only. No tested-allele protein, strain TaxID, sample/genome ID, MIC or clinical category assigned.	—	Saccharomyces cerevisiae `NCBITaxon:4932` FUR1	FUR1	PMID:37856537 (Direct 5-FC results: sec003/sec005; Figures 2 and 4C. Cohort association.) UniProtKB:P18562 (FUR1 reference identity only; release 2026_03.) Relative colony-growth area under the curve

REDUCED_PERMEABILITY 2

REDUCED_PERMEABILITY
Determinant	ARO ID	Organism	Gene families	Evidence
Aspergillus spp. fcyB conferring resistance to 5-flucytosine via reduced permeability	ARO:3007642	not organism-specific	—	ARO:3007642 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3007558 (5-flucytosine); database assertion, not a primary citation.)
Candida spp. FCY2 conferring resistance to 5-flucytosine via reduced permeability	ARO:3007665	not organism-specific	—	ARO:3007665 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3007558 (5-flucytosine); database assertion, not a primary citation.)

UNKNOWN 1

UNKNOWN
Determinant	ARO ID	Organism	Gene families	Evidence
Cryptococcus spp. UXS1 conferring resistance to 5-flucytosine via absence	ARO:3007568	not organism-specific	—	ARO:3007568 (CARD/ARO asserts confers_resistance_to_antibiotic ARO:3007558 (5-flucytosine); database assertion, not a primary citation.)

Discussions

Open questions, knowledge gaps and curation todos attached to this compound.

CURATION_TODO OPEN

Resolve the URA6 species-scope discrepancy and exact FungAMR source-row mapping before assigning a tested allele or protein to ARO:3009633.

The CARD label names Cryptococcus neoformans, but the independently identified primary study by Chang et al. (2021) places its URA6 comparison in Cryptococcus gattii WM276-derived material. This is a potential source species-scope conflict, not a proven correction to CARD: the exact FungAMR row-to-primary-paper crosswalk has not been verified. Preserve the source-owned assertion as database provenance and do not transfer the WM276 evidence to C. neoformans H99. The separate H99 UniProt identity candidate does not establish an H99 resistance phenotype.

Attached to: resistance_mechanisms#ARO:3009633

Curation history

SEEDED_FROM_SOURCES 2026-08-30 · seed_from_sources
Seeded from data/raw/ inventories (ARO, CHEBI)
RESEEDED_FROM_SOURCES 2026-08-30 · seed_from_sources
Re-seeded from updated data/raw/ inventories
RESEEDED_FROM_SOURCES 2026-08-30 · seed_from_sources
Re-seeded from updated data/raw/ inventories
RESEEDED_FROM_SOURCES 2026-08-31 · seed_from_sources
Re-seeded from updated data/raw/ inventories
RESEEDED_FROM_SOURCES 2026-08-31 · seed_from_sources
Re-seeded from updated data/raw/ inventories
RESEEDED_FROM_SOURCES 2026-09-10 · seed_from_sources
Re-seeded from updated data/raw/ inventories
CURATED_RESISTANCE_EVIDENCE 2026-10-08 · codex · LLM-assisted
Added two directly supported flucytosine FUR1 cohort associations with species grounding and reference-only UniProt context. Preserved eight CARD assertions; no exact allele, experimental protein, genome, MIC or clinical call inferred.
CURATED_RESISTANCE_EVIDENCE 2026-10-08 · codex · LLM-assisted
Restored original YAML key ordering after serialization review. No biological fields, source assertions or prior history values changed.
CURATED_EVIDENCE_SCOPE_DISCUSSION 2026-10-14 · codex · LLM-assisted
Added a qualified URA6 species-scope discussion: independently identified primary evidence uses C. gattii WM276, while the CARD label names C. neoformans. The exact FungAMR row crosswalk remains unverified. Preserved eight CARD assertions, two FUR1 associations and SEEDED status; reference proteins and taxonomy are not tested-allele or phenotype assignments.

Provenance

Seeded by scripts/seed_from_sources.py from the committed inventories in data/raw/. View the record (YAML).

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