Exact Mass: 268.13106700000003
Exact Mass Matches: 268.13106700000003
Found 117 metabolites which its exact mass value is equals to given mass value 268.13106700000003,
within given mass tolerance error 0.0002 dalton. Try search metabolite list with more accurate mass tolerance error
4.0E-5 dalton.
Kamahine C
5,5-dihydroxy-4,4,8,8-tetramethyl-7-oxaspiro[bicyclo[3.2.1]octane-6,2-oxolan]-3-en-2-one
Kamahine A is a constituent of honey from Weinmannia racemosa. Found in honey from Kamali (Weinmannia racemosa)
3-carboxy-4-methyl-5-pentyl-2-furanpropanoic acid
2-(2-carboxyethyl)-4-methyl-5-pentylfuran-3-carboxylic acid
3-Carboxy-4-methyl-5-pentyl-2-furanpropanoic acid is a urofuranic acid. Urofuranic acids are usually derived from furanoic acids, and have two carboxyl groups at the 3- and 4-positions of the furan ring.
Papyracon B
[1aR-[1aalpha,3abeta,5E(S*),7alpha,7aS*]]-Tetrahydro-3a,7-dihydroxy-5-(2-hydroxypropylidene)-2,2-dimethyl-1H,5H-cyclopropa[c]benzofuran-4(3aH)-one
Papyracon C
[1aR-[1aalpha,3abeta,5E(R*),7a,7aS*]]-Tetrahydro-3a,7-dihydroxy-5-(2-hydroxypropylidene)-2,2-dimethyl-1H,5H-cyclopropa[c]benzofuran-4(3aH)-one
8a-hydroxy-7-methoxy-3,3,6,8,8-pentamethyl-1,2-benzodioxin-5-one
8a-hydroxy-7-methoxy-3,3,6,8,8-pentamethyl-1,2-benzodioxin-5-one
butyl 5-[(1R)-1-hydroxyethyl]-gamma-oxofuran-2-butanoate
butyl 5-[(1R)-1-hydroxyethyl]-gamma-oxofuran-2-butanoate
(+-)-(2Xi,3aXi)-2-Methoxy-(3ar,7at)-hexahydro-spiro[cyclopropan-1,2-indan]-2r,3c-dicarbonsaeure|(+-)-(2Xi,3aXi)-2-methoxy-(3ar,7at)-hexahydro-spiro[cyclopropane-1,2-indan]-2r,3c-dicarboxylic acid
(+-)-(2Xi,3aXi)-2-Methoxy-(3ar,7at)-hexahydro-spiro[cyclopropan-1,2-indan]-2r,3c-dicarbonsaeure|(+-)-(2Xi,3aXi)-2-methoxy-(3ar,7at)-hexahydro-spiro[cyclopropane-1,2-indan]-2r,3c-dicarboxylic acid
(1S,2Z,4S)-1-butyl-4-hydroxy-4-[(2S)-5-oxo-2,5-dihydrofuran-2-yl]but-2-en-1-yl acetate|5S-[(4S-acetyloxy)-(1S-hydroxy)-2Z-octenyl]-2(5H)-furanone|pectinolide H
(1S,2Z,4S)-1-butyl-4-hydroxy-4-[(2S)-5-oxo-2,5-dihydrofuran-2-yl]but-2-en-1-yl acetate|5S-[(4S-acetyloxy)-(1S-hydroxy)-2Z-octenyl]-2(5H)-furanone|pectinolide H
3-hydroxy-5-methoxy-2,4-dimethyl-4-(2-methylbutyryloxy)-2,5-cyclohexadien-1-one
3-hydroxy-5-methoxy-2,4-dimethyl-4-(2-methylbutyryloxy)-2,5-cyclohexadien-1-one
4-acetyl-2-[(1E)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3(2H)-one|huaspenone B
4-acetyl-2-[(1E)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3(2H)-one|huaspenone B
5-(5-carboxymethyl-2-oxocyclopentyl)-3-pentenyl acetate
5-(5-carboxymethyl-2-oxocyclopentyl)-3-pentenyl acetate
3-hydroxy-5-methoxy-2,6-dimethyl-6-(2-methylbutyryloxy)-2,4-cyclohexadien-1-one
3-hydroxy-5-methoxy-2,6-dimethyl-6-(2-methylbutyryloxy)-2,4-cyclohexadien-1-one
Acetic acid 3-(3,4,5-trimethoxyphenyl)propyl ester
Acetic acid 3-(3,4,5-trimethoxyphenyl)propyl ester
(R)-2-Methylbutyric acid (S)-1,5-dimethyl-2-oxo-4-methoxy-6-hydroxy-3,5-cyclohexadienyl ester
(R)-2-Methylbutyric acid (S)-1,5-dimethyl-2-oxo-4-methoxy-6-hydroxy-3,5-cyclohexadienyl ester
2-(2-carboxyethyl)-4-methyl-5-pentylfuran-3-carboxylic acid
2-(2-carboxyethyl)-4-methyl-5-pentylfuran-3-carboxylic acid
3-carboxy-4-methyl-5-pentyl-2-furanpropionate (3-CMPFP)
new_metabolite-834158
Belongs to the class of organic compounds known as furanoid fatty acids. These are fatty acids containing a 5-alkylfuran-2-alkanoic acid
3-carboxy-4-methyl-5-pentyl-2-furanpropanoic acid
2-(2-carboxyethyl)-4-methyl-5-pentylfuran-3-carboxylic acid
Belongs to the class of organic compounds known as furanoid fatty acids. These are fatty acids containing a 5-alkylfuran-2-alkanoic acid.
8a-hydroxy-3,3,6,6,8,8-hexamethyl-1,2-benzodioxine-5,7-dione
8a-hydroxy-3,3,6,6,8,8-hexamethyl-1,2-benzodioxine-5,7-dione
(2s,3s)-2-[(1z,3s)-3-hydroxyhept-1-en-1-yl]-6-oxo-2,3-dihydropyran-3-yl acetate
(2s,3s)-2-[(1z,3s)-3-hydroxyhept-1-en-1-yl]-6-oxo-2,3-dihydropyran-3-yl acetate
(1s,2s,3r)-3-acetyl-2-(4-carboxy-4-methylbut-3-en-1-yl)-2-methylcyclobutane-1-carboxylic acid
(1s,2s,3r)-3-acetyl-2-(4-carboxy-4-methylbut-3-en-1-yl)-2-methylcyclobutane-1-carboxylic acid
{4-[(2r)-1,2-dihydroxypropan-2-yl]-3-hydroxyphenyl}methyl 2-methylpropanoate
{4-[(2r)-1,2-dihydroxypropan-2-yl]-3-hydroxyphenyl}methyl 2-methylpropanoate
(3r,4as,6r)-6,8-dihydroxy-3-(4-oxopentyl)-3,4,4a,5,6,7-hexahydro-2-benzopyran-1-one
(3r,4as,6r)-6,8-dihydroxy-3-(4-oxopentyl)-3,4,4a,5,6,7-hexahydro-2-benzopyran-1-one
(2s)-4-acetyl-2-[(1e,5s)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3-one
(2s)-4-acetyl-2-[(1e,5s)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3-one
methyl 2-hydroxy-3-[4-hydroxy-2,5-bis(prop-1-en-1-yl)oxolan-3-ylidene]propanoate
methyl 2-hydroxy-3-[4-hydroxy-2,5-bis(prop-1-en-1-yl)oxolan-3-ylidene]propanoate
methyl (2r)-2-hydroxy-3-[(2r,3e,4s,5s)-4-hydroxy-2,5-bis[(1e)-prop-1-en-1-yl]oxolan-3-ylidene]propanoate
methyl (2r)-2-hydroxy-3-[(2r,3e,4s,5s)-4-hydroxy-2,5-bis[(1e)-prop-1-en-1-yl]oxolan-3-ylidene]propanoate
4-[2-(4-hydroxy-2-methyl-5-oxooxolan-2-yl)ethyl]-3-propyl-5h-furan-2-one
4-[2-(4-hydroxy-2-methyl-5-oxooxolan-2-yl)ethyl]-3-propyl-5h-furan-2-one
7,8-dihydroxy-isobutyryl-thymol
NA
{"Ingredient_id": "HBIN012986","Ingredient_name": "7,8-dihydroxy-isobutyryl-thymol","Alias": "NA","Ingredient_formula": "C14H20O5","Ingredient_Smile": "CC(C)C(=O)OCC(C)(C1=C(C=C(C=C1)CO)O)O","Ingredient_weight": "NA","OB_score": "NA","CAS_id": "NA","SymMap_id": "NA","TCMID_id": "5920","TCMSP_id": "NA","TCM_ID_id": "NA","PubChem_id": "NA","DrugBank_id": "NA"}
[1-(acetyloxy)-7-methyl-1h,4ah,5h,6h,7h,7ah-cyclopenta[c]pyran-4-yl]methyl acetate
[1-(acetyloxy)-7-methyl-1h,4ah,5h,6h,7h,7ah-cyclopenta[c]pyran-4-yl]methyl acetate
4-methoxy-1,3-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
4-methoxy-1,3-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
(1r,3s,6r,8e,10s)-6,10-dihydroxy-8-[(2s)-2-hydroxypropylidene]-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
(1r,3s,6r,8e,10s)-6,10-dihydroxy-8-[(2s)-2-hydroxypropylidene]-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
(3s,5r,6r,6's)-5,6-dihydroxy-6,6'-dimethyl-4,5-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-7-one
(3s,5r,6r,6's)-5,6-dihydroxy-6,6'-dimethyl-4,5-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-7-one
methyl (2r,5r,6r)-5-hydroxy-2-[(1s,2e)-1-hydroxybut-2-en-1-yl]-6-[(1e)-prop-1-en-1-yl]-5,6-dihydro-2h-pyran-3-carboxylate
methyl (2r,5r,6r)-5-hydroxy-2-[(1s,2e)-1-hydroxybut-2-en-1-yl]-6-[(1e)-prop-1-en-1-yl]-5,6-dihydro-2h-pyran-3-carboxylate
12-hydroxy-6,14-dimethyl-1,7-dioxacyclotetradeca-3,9-diene-2,8-dione
12-hydroxy-6,14-dimethyl-1,7-dioxacyclotetradeca-3,9-diene-2,8-dione
4-acetyl-2-(5-hydroxyhex-1-en-1-yl)-5-methoxy-2-methylfuran-3-one
4-acetyl-2-(5-hydroxyhex-1-en-1-yl)-5-methoxy-2-methylfuran-3-one
[(1r,4ar,7r,7as)-1-(acetyloxy)-7-methyl-1h,4ah,5h,6h,7h,7ah-cyclopenta[c]pyran-4-yl]methyl acetate
[(1r,4ar,7r,7as)-1-(acetyloxy)-7-methyl-1h,4ah,5h,6h,7h,7ah-cyclopenta[c]pyran-4-yl]methyl acetate
4-acetyl-2-[(1e)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3-one
4-acetyl-2-[(1e)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3-one
(1s,3r,6s,8e,10s)-6,10-dihydroxy-8-[(2s)-2-hydroxypropylidene]-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
(1s,3r,6s,8e,10s)-6,10-dihydroxy-8-[(2s)-2-hydroxypropylidene]-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
(3s,6s,6's,7r)-6,7-dihydroxy-6,6'-dimethyl-4,7-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-5-one
(3s,6s,6's,7r)-6,7-dihydroxy-6,6'-dimethyl-4,7-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-5-one
(8as)-8a-hydroxy-7-methoxy-3,3,6,8,8-pentamethyl-1,2-benzodioxin-5-one
(8as)-8a-hydroxy-7-methoxy-3,3,6,8,8-pentamethyl-1,2-benzodioxin-5-one
(4s,6s)-6-[(1s,2e,4e)-1,6-dihydroxyhexa-2,4-dien-1-yl]-3,4-dihydroxy-2,4-dimethylcyclohex-2-en-1-one
(4s,6s)-6-[(1s,2e,4e)-1,6-dihydroxyhexa-2,4-dien-1-yl]-3,4-dihydroxy-2,4-dimethylcyclohex-2-en-1-one
4-{2-[(2r,4r)-4-hydroxy-2-methyl-5-oxooxolan-2-yl]ethyl}-3-propyl-5h-furan-2-one
4-{2-[(2r,4r)-4-hydroxy-2-methyl-5-oxooxolan-2-yl]ethyl}-3-propyl-5h-furan-2-one
butyl 4-{5-[(1r)-1-hydroxyethyl]furan-2-yl}-4-oxobutanoate
butyl 4-{5-[(1r)-1-hydroxyethyl]furan-2-yl}-4-oxobutanoate
4-methoxy-1,5-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
4-methoxy-1,5-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
6,7-dihydroxy-6,6'-dimethyl-4,7-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-5-one
6,7-dihydroxy-6,6'-dimethyl-4,7-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-5-one
(3z,6r,9z,12s)-12-hydroxy-6,14-dimethyl-1,7-dioxacyclotetradeca-3,9-diene-2,8-dione
(3z,6r,9z,12s)-12-hydroxy-6,14-dimethyl-1,7-dioxacyclotetradeca-3,9-diene-2,8-dione
(2s,3r,4r,5r,6r)-2-methyl-6-(2-phenylethoxy)oxane-3,4,5-triol
(2s,3r,4r,5r,6r)-2-methyl-6-(2-phenylethoxy)oxane-3,4,5-triol
(3r)-2-{3-methoxy-2,6-dimethyl-7ah-furo[2,3-b]pyran-4-yl}butane-2,3-diol
(3r)-2-{3-methoxy-2,6-dimethyl-7ah-furo[2,3-b]pyran-4-yl}butane-2,3-diol
(3z,11z)-2,13-dihydroxy-7-methyl-6,15-dioxabicyclo[12.1.0]pentadeca-3,11-dien-5-one
(3z,11z)-2,13-dihydroxy-7-methyl-6,15-dioxabicyclo[12.1.0]pentadeca-3,11-dien-5-one
[4-(1,2-dihydroxypropan-2-yl)-3-hydroxyphenyl]methyl 2-methylpropanoate
[4-(1,2-dihydroxypropan-2-yl)-3-hydroxyphenyl]methyl 2-methylpropanoate
(5r,6r,7r,8s)-8-ethyl-5,6,7-trihydroxy-2,3,8-trimethyl-6,7-dihydro-5h-chromen-4-one
(5r,6r,7r,8s)-8-ethyl-5,6,7-trihydroxy-2,3,8-trimethyl-6,7-dihydro-5h-chromen-4-one
(8ar)-8a-hydroxy-3,3,6,6,8,8-hexamethyl-1,2-benzodioxine-5,7-dione
(8ar)-8a-hydroxy-3,3,6,6,8,8-hexamethyl-1,2-benzodioxine-5,7-dione
8-ethyl-5,6,7-trihydroxy-2,3,8-trimethyl-6,7-dihydro-5h-chromen-4-one
8-ethyl-5,6,7-trihydroxy-2,3,8-trimethyl-6,7-dihydro-5h-chromen-4-one
5,6-dihydroxy-6,6'-dimethyl-4,5-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-7-one
5,6-dihydroxy-6,6'-dimethyl-4,5-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-7-one
7-hexyl-4-methoxy-4ah,7h,7ah-furo[3,4-b]pyran-2,5-dione
7-hexyl-4-methoxy-4ah,7h,7ah-furo[3,4-b]pyran-2,5-dione
(1s,2z,4s)-1-hydroxy-1-[(2s)-5-oxo-2h-furan-2-yl]oct-2-en-4-yl acetate
(1s,2z,4s)-1-hydroxy-1-[(2s)-5-oxo-2h-furan-2-yl]oct-2-en-4-yl acetate
butyl 4-[5-(1-hydroxyethyl)furan-2-yl]-4-oxobutanoate
butyl 4-[5-(1-hydroxyethyl)furan-2-yl]-4-oxobutanoate
(2s)-4-acetyl-2-[(5s)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3-one
(2s)-4-acetyl-2-[(5s)-5-hydroxyhex-1-en-1-yl]-5-methoxy-2-methylfuran-3-one
6,7-dihydroxy-6-methyl-2-(2-methylpropanoyl)-4,5,7,7a-tetrahydro-3ah-1-benzofuran-3-carbaldehyde
6,7-dihydroxy-6-methyl-2-(2-methylpropanoyl)-4,5,7,7a-tetrahydro-3ah-1-benzofuran-3-carbaldehyde
[(1s,4as,7s,7ar)-1-(acetyloxy)-7-methyl-1h,4ah,5h,6h,7h,7ah-cyclopenta[c]pyran-4-yl]methyl acetate
[(1s,4as,7s,7ar)-1-(acetyloxy)-7-methyl-1h,4ah,5h,6h,7h,7ah-cyclopenta[c]pyran-4-yl]methyl acetate
(1r)-4-methoxy-1,5-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
(1r)-4-methoxy-1,5-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
(3z,6r,9z,11r,13r)-11-(hydroxymethyl)-6,13-dimethyl-1,7-dioxacyclotrideca-3,9-diene-2,8-dione
(3z,6r,9z,11r,13r)-11-(hydroxymethyl)-6,13-dimethyl-1,7-dioxacyclotrideca-3,9-diene-2,8-dione
(1r)-4-methoxy-1,3-dimethyl-2,6-dioxocyclohex-3-en-1-yl (2r)-2-methylbutanoate
(1r)-4-methoxy-1,3-dimethyl-2,6-dioxocyclohex-3-en-1-yl (2r)-2-methylbutanoate
1-hydroxy-1-(5-oxo-2h-furan-2-yl)oct-2-en-4-yl acetate
1-hydroxy-1-(5-oxo-2h-furan-2-yl)oct-2-en-4-yl acetate
6-(1,6-dihydroxyhexa-2,4-dien-1-yl)-3,4-dihydroxy-2,4-dimethylcyclohex-2-en-1-one
6-(1,6-dihydroxyhexa-2,4-dien-1-yl)-3,4-dihydroxy-2,4-dimethylcyclohex-2-en-1-one
(3s,6s,6's,7s)-6,7-dihydroxy-6,6'-dimethyl-4,7-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-5-one
(3s,6s,6's,7s)-6,7-dihydroxy-6,6'-dimethyl-4,7-dihydro-1h-spiro[cyclopenta[c]pyran-3,2'-oxan]-5-one
(2r)-2,3-dihydroxy-2-(2-hydroxy-4-methylphenyl)propyl 2-methylpropanoate
(2r)-2,3-dihydroxy-2-(2-hydroxy-4-methylphenyl)propyl 2-methylpropanoate
(1r)-4-methoxy-1,3-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
(1r)-4-methoxy-1,3-dimethyl-2,6-dioxocyclohex-3-en-1-yl 2-methylbutanoate
(8as)-8a-hydroxy-3,3,6,6,8,8-hexamethyl-1,2-benzodioxine-5,7-dione
(8as)-8a-hydroxy-3,3,6,6,8,8-hexamethyl-1,2-benzodioxine-5,7-dione
5,5'-dihydroxy-4,4',8,8-tetramethyl-7-oxaspiro[bicyclo[3.2.1]octane-6,2'-oxolan]-3-en-2-one
5,5'-dihydroxy-4,4',8,8-tetramethyl-7-oxaspiro[bicyclo[3.2.1]octane-6,2'-oxolan]-3-en-2-one
2,3-dihydroxy-2-(2-hydroxy-4-methylphenyl)propyl 2-methylpropanoate
2,3-dihydroxy-2-(2-hydroxy-4-methylphenyl)propyl 2-methylpropanoate
6,10-dihydroxy-8-(2-hydroxypropylidene)-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
6,10-dihydroxy-8-(2-hydroxypropylidene)-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
(1s,3r,6s,8e,10s)-6,10-dihydroxy-8-[(2r)-2-hydroxypropylidene]-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
(1s,3r,6s,8e,10s)-6,10-dihydroxy-8-[(2r)-2-hydroxypropylidene]-4,4-dimethyl-5-oxatricyclo[4.4.0.0¹,³]decan-7-one
methyl 2-hydroxy-3-[(2r,3e,4s,5s)-4-hydroxy-2,5-bis[(1e)-prop-1-en-1-yl]oxolan-3-ylidene]propanoate
methyl 2-hydroxy-3-[(2r,3e,4s,5s)-4-hydroxy-2,5-bis[(1e)-prop-1-en-1-yl]oxolan-3-ylidene]propanoate
(3z,6r,10e,13r)-11-(hydroxymethyl)-6,13-dimethyl-1,7-dioxacyclotrideca-3,10-diene-2,8-dione
(3z,6r,10e,13r)-11-(hydroxymethyl)-6,13-dimethyl-1,7-dioxacyclotrideca-3,10-diene-2,8-dione
6,8-dihydroxy-3-(4-oxopentyl)-3,4,4a,5,6,7-hexahydro-2-benzopyran-1-one
6,8-dihydroxy-3-(4-oxopentyl)-3,4,4a,5,6,7-hexahydro-2-benzopyran-1-one
(1z,3s)-1-[(2s,3s)-3-hydroxy-6-oxo-2,3-dihydropyran-2-yl]hept-1-en-3-yl acetate
(1z,3s)-1-[(2s,3s)-3-hydroxy-6-oxo-2,3-dihydropyran-2-yl]hept-1-en-3-yl acetate
(3as,6r,7s,7ar)-6,7-dihydroxy-6-methyl-2-(2-methylpropanoyl)-4,5,7,7a-tetrahydro-3ah-1-benzofuran-3-carbaldehyde
(3as,6r,7s,7ar)-6,7-dihydroxy-6-methyl-2-(2-methylpropanoyl)-4,5,7,7a-tetrahydro-3ah-1-benzofuran-3-carbaldehyde
2-{3-methoxy-2,6-dimethyl-7ah-furo[2,3-b]pyran-4-yl}butane-2,3-diol
2-{3-methoxy-2,6-dimethyl-7ah-furo[2,3-b]pyran-4-yl}butane-2,3-diol
(1r,5r)-4-methoxy-1,5-dimethyl-2,6-dioxocyclohex-3-en-1-yl (2r)-2-methylbutanoate
(1r,5r)-4-methoxy-1,5-dimethyl-2,6-dioxocyclohex-3-en-1-yl (2r)-2-methylbutanoate
(7s)-7-hexyl-4-methoxy-4ah,7h,7ah-furo[3,4-b]pyran-2,5-dione
(7s)-7-hexyl-4-methoxy-4ah,7h,7ah-furo[3,4-b]pyran-2,5-dione