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 1.6E-6 dalton. Try search metabolite list with more accurate mass tolerance error
3.2E-7 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