Regioselectivity in the formation of norbornene-fused pyrazoles: preparation of 1-substituted derivatives of 4,5,6,7-tetrahydro-1H-4,7-methanoindazole

The structural characteristics of (±)-(exo,exo)-3-(hydroxymethylene)-5,6-(isopropylidenedioxy)bicyclo[2.2.1]heptan-2-one make the reactions between this β-diketone and hydrazines particularly interesting for elucidating the mechanism of pyrazole formation. The isolation and X-ray structure determination of two 5-hydroxy substituted Δ²-pyrazolines [(±)-(3aR*,4R*,5R*,6S*,7R*,7aR*)-7a-hydroxy-5,6-(isopropylidenedioxy)-3a,4,5,6,7,7a-hexahydro-4,7-methano-1H-indazole] and [(±)-(3aS*,4R*,5R*,6S*,7R*,7aR*)-7a-hydroxy-5,6-(isopropylidene-dioxy)-1-phenyl-3a,4,5,6,7,7a-hexa-hydro-4,7-methano-1H-indazole] has been determinant for proposing a mechanism. Besides B3LYP/6-31G* calculations have been carried out on all intermediate dihydroxypyrazolidines and 5-hydroxypyrazolines. Finally, the annular tautomerism of the NH-methanotetrahydroindazoles has been studied both experimentally (¹³C NMR) and theoretically: the Mills-Nixon effect favours the 2H-tautomer.     

Diels–Alder adducts of medium-ring carbocyclic dienes prepared by rearrangement of catalytically generated cyclic oxonium ylides

The novel bicyclic and tricyclic systems di­methyl (4aS*,6S*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexa­hydro-2H-benzo­cyclo­hept­ene-3,4-di­carboxyl­ate, C₁₆H₂₀O₆, (I), di­methyl (4aS*,6R*)-6-methoxy-7-oxo-4a,5,6,7,8,9-hexa­hydro-2H-benzo­cyclo­hept­ene-3,4-di­carboxyl­ate, C₁₆H₂₀O₆, (II), (3aS*,9R*,10aS*,10bR*)-9-methoxy-2-oxa-1,3a,4,6,7,8,9,10,10a,10b-deca­hydro-3H-cyclo­hepta­[e]­indene-1,3,8-trione, C₁₄H₁₆O₅, (III), and (1S*,2R*,9S*,10aR*)-9-methoxy-8-oxo-1,2,3,5,6,7,8,9,10,10a-deca­hydrobenzo­cyclo­octene-1,2-di­carboxyl­ic acid, C₁₅H₂₀O₆, (IV), have been crystallographically characterized, allowing the determination of the relative configuration of the stereogenic centres. The poor quality of the di­carboxyl­ic acid crystals necessitated the use of synchrotron radiation.     

Enantioselective syntheses of isoprostane and iridoid lactones intermediates by enzymatic transesterification

Crude Pseudomonas cepacia lipase (Amano PS-30) is a suitable biocatalyst for the kinetic resolution of the 1,2-cis-disubstituted cyclopentanoid building block (3aR*,4R*,6aS*)-(±)-4-hydroxymethyl-3,3a,4,6a-tetrahydrocyclopenta[b]furan-2-one through enantioselective transesterification. Enantiomerically enriched acetic acid (3aS,4S,6aR)-(+)-2-oxo-3,3a,4,6a-tetrahydro-2H-cyclopenta[b]furan-4-yl methyl ester was utilized in a formal synthesis of the iridoids (+)-isoiridomyrmecin and (−)-teucriumlactone.     

New Sesquiterpenoids from Salvia castanea Diels f. tomentosa

Two new sesquiterpenoids, castanin A (= 4R*,5R*,5aS*,8S*,8aR*,8bR*)‐8‐formyl‐4,5,5a,6,7,8,8a,8b‐octahydro‐5,8b‐dihydroxy‐3,5a,8‐trimethyl‐2‐oxo‐2H‐indeno[4,5‐b]furan‐4‐yl acetate; 1 ) and castanin B (= 1aS*,6R*,6aS*,7aR*,9aR*)‐1a,2,6,6a,7a,8,9,9a‐octahydro‐1a,5,7a‐trimethylbisoxireno[4,5 : 8,9]cyclodeca[1,2‐b]furan‐6‐yl acetate; 2 ) were isolated from the aerial parts of Salvia castanea Diels f. tomentosa, together with two known compounds, oplophanone and 1β,6α‐dihydroxyeudesm‐4(14)‐ene. Their structures were elucidated by spectroscopic analyses and, in the case of 2 , also by X‐ray crystallography. Castanin A ( 1 ) represents a novel sesquiterpenoid, with a contracted ring A, derived from eudesmanolide. A possible biogenetic pathway is proposed.     

Studies on ketene and its derivatives. CXI . Photoreaction of diketene with 2(1H)-quinolone derivatives

Photoreaction of diketene with 4-methyl-2(1H)-quinolone and 1,4-dimethyl-2(1H)-quinolone gave 2R*,2aR*,SbR*- and 2R*,2aS*8bS*-8b-methyl-3-oxo-1,2,2a,3,4,8b-hexahydrocyclobuta[c]quinoline-2-spiro-2′-(oxetan)-4′-one ( 6a and 6b ), and their 4-methyl derivatives 7a and 7b , respectively. Thermolysis of compounds 6 and 7 afforded 2aR*,8bS*-8b-methyl-2-methylene-3-oxo-1,2,2a,3,4,8b-hexahydrocyclobuta[c]quinoline ( 8 ) and its 4-methyl derivatives 9 , respectively. Similarly, photolysis of diketene and 4-acetoxy-2(1H)-quinolone gave 1R*,2aS*,8bS*- and 1R*,2aR*,8bR*-8b-acetoxy-3-oxo-1,2,2a,3,4,8b-hexahydrocyclobuta[c]-quinoline ( 11a and 11b ). Alcoholysis of compounds 11a and 11b with hydrogen chloride in methanol gave 1-hydroxy-1-(methoxycarbonyl)methylcyclobuta[c]quinoline derivative 12 and 13 which were transformed to 4-acetyl-3-methyl-2(1H)-quinolone ( 15 ) by further alcoholysis. Photoreaction of diketene with 2(1H)-quinolone derivatives gave the corresponding cyclobuta[c]quinoline spirooxetanone derivatives 18 and 23 , which, by thermolysis, were transformed to 2-methylenecyclobuta[c]quinoline 23 and 25 , respectively.     

Furopyridines. XVIII. Photocycloaddition of furo[2,3-c]pyridin-7(6H)-one with acrylonitrile

The photocycloaddition of furo[2,3-c]pyridin-7(6H)-one ( 1 ) and its N-mefhyl derivative ( 1-Me ) to acrylonitrile has been studied. The structures of the photoadducts isolated by colum chromatography were determined by the nuclear magnetic resonance spectroscopy and single crystal X-ray analysis. The cyclo-addition of 1 afforded an adduct 2 at the carbonyl oxygen and 8-cyano-8,9-dihydrofuro[d]azocin-7(6H)-one ( 3 ), and the addition of 1-Me the N-methyl derivative 3-Me of 3 , (9S*)-9-cyano-6-methyl-3a,7a-dihydro-3a,7a-ethanofuro[2,3-c]pyridin-7(6H)-one ( 4 ), (2S*, 2aR*, 7bR*)- ( 5 ) and (1R*, 2aS*, 7bS*)-2-cyano-3-methyl-4-oxo-1,2,2a,3,4,7b-hexahydrocyclobuta[e]furo[2,3-c]pyridine ( 6 ).     

Packing in three cyclooctitol acetates

Three cyclooctitol derivatives, in the form of a tetraacetate, (1S*,2R*,3S*,4S*)‐2,3,4‐triacetoxycyclooctan‐1‐ylmethyl acetate, C₁₇H₂₆O₈, and two regioisomeric acetonide triacetates, (3aS*,4R*,8S*,9S*,9aS*)‐8,9‐diacetoxy‐2,2‐dimethylcyclooctano[d][1,3]dioxan‐4‐ymethyl acetate and (3aS,4R,7S,9R,9aS)‐7,9‐diacetoxy‐2,2‐dimethylcyclooctano[d][1,3]dioxan‐4‐ylmethyl acetate, both C₁₈H₂₈O₈, have been studied. The conformation of the cyclooctane ring in the three compounds is quite close to the boat–chair form of the parent hydrocarbon. Packing is effected through weak C—H...O and van der Waals contacts.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

A new strategy in enantioselective intramolecular hetero Diels-Alder reaction: catalytic double asymmetric induction during the tandem transetherification-intramolecular hetero Diels-Alder reaction of methyl (E)-4-methoxy-2-oxo-3-butenoate with rac-6-methyl-5-hepten-2-ol

An efficient catalytic double asymmetric induction during the tandem transetherification-intramolecular hetero Diels-Alder reaction has been developed. The enantioselective tandem reaction of methyl (E)-4-methoxy-2-oxo-3-butenoate with rac-6-methyl-5-hepten-2-ol has been achieved to provide methyl (2R,4aS,8aR)-3,4,4a,8a-tetrahydro-2,5,5-trimethyl-2H,5H-pyrano[4,3-b]-pyran-7-carboxylate in good yield with effective kinetic resolution (up to 95% selectivity), high diastereoselectivity (up to 92% de), and high enantioselectivity (up to 97% ee) in the presence of (S,S)-tert-Bu-bis(oxazoline)-Cu(SbF₆)₂ and 5 Å molecular sieves.     

Tailor-made chiral pyranopyrans based on glucose and galactose and studies on self-assembly of some crystals and low molecular weight organogel (LMOG)

InCl₃ catalyzed reactions of 2-C-acetoxymethylglycal derivatives with different phenolic compounds resulted in the formation of sugar based pyranoarenopyrans in good yields and moderate to excellent diastereoselectivity in favor of 10aR- or 12aR- or 14aR-products. One of the synthesized compounds, viz. (2R,3R,12aR)-2,3,5,12a-tetrahydro-2-methoxymethyl-3-methoxypyrano[2,3-b]naphtho[1,2-e]pyran gelated polar solvents like MeOH, EtOH and non-polar solvents like pentane, hexane, heptane, octane, pet. ether, etc. The SEM picture of the corresponding hexane xerogel exhibited a rare type of microtubular gel assembly, whereas the SEM pictures of MeOH and pet. ether xerogels showed different types of three-dimensional network. Study of the MeOH gel by Fluorescence spectroscopy, ¹H NMR and X-ray powder diffraction analysis indicated that the supramolecular assembly in the MeOH gel can be attributed to π-stacking. The crystal packing of (2R,3R,10aR)-3,10a-dihydro-2-methoxymethyl-3-methoxy-7-methyl-2H,5H-pyrano[2,3-b][1]benzopyran, a benzopyran analogue of the above organogelator was stabilized by C-H?O and C-H?π hydrogen bonds forming one-dimensional columns parallel to the [001] direction, whereas the corresponding benzopyran 3-epimer showed only C-H?O hydrogen bonds among the molecules.     

Reactions of N- and C-alkenylanilines: IX. Synthesis, oxidation, and nitration of some 7-methyl-1,3a,4,8b-tetrahydrocyclopenta[b]indoles

Heating of 4-acyl-3-iodo-7-methyl-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indoles in piperidine gave 4-acyl-7-methyl-1,3a,4,8b-tetrahydrocyclopenta[b]indoles which were oxidized with KMnO4 to obtain the corresponding 4-acyl-7-methyl-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indole-1,2-diols. Oxidation of 4-acyl-7-methyl-1,3a,4,8b-tetrahydrocyclopenta[b]indoles at the olefinic double bond with hydrogen peroxide in acetonitrile in the presence of formic acid afforded stereoisomeric epoxides with cis and trans orientation of the nitrogen-containing and oxirane rings. Nitration with a mixture of ammonium nitrate and trifluoroacetic anhydride produced 5-nitro derivatives. The structure of 1-{(1aR*,1bR*,6bS*,7aS*)-5-methyl-1a,1b,2,6b,7,7ahexahydrooxireno[4,5]cyclopenta[1,2-b]indol-2-yl}ethanone was determined by X-ray analysis.     

Novel Trinor-eremophilanes (Dendryphiellin B,C, and D), Eremophilanes (Dendryphiellin E,F, and G), and Branched C9-Carboxylic Acids (Dendryphiellic Acid A and B) from the Marine Deuteromycete Dendryphiella salina (SUTHERLAND) PUGHet NICOT

Further investigation of global extracts from cultures of the marine deuteromycete Dendryphiella salina leads to the isolation of three novel trinor-eremophilanes esterified by branched C₉-carboxylic acids, dendryphiellin B (= (+)-(1R*,2S*,7R*,8aR*)-1,2,6,7,8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6R*, 2E, 4E)-6-hydroxy-6-methylocta-2,4-dienoate; (+)- 2 ), dendryphiellin C (=(+)-(1R*, 2S*, 7R*, 8aR*)-1,2,6,7,8,8a-hexa-hydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6S, 2E, 4E)-6-methylocta-2,4-dienoate; (+)- 3 )), and dendryphiellin D (=(+)-(1R*, 2S*, 7R*, 8aR*)-1,2,6,7(8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2-yl (6R*,2E,4E)-6-(hydroxymethyl)octa-2,4-dienoate; (+)- 4 ). An intact eremophilane, dendryphiellin E ( 5 ), and its ethanolysis product dendryphiellin F whose absolute configuration is represented by structural formula (+)- 6 are also isolated from the above extracts. Dendryphiellin E exists as an open form 5a in equilibrium with a closed form 5b . A similar equilibrium exists between the open form 8a and the closed form 8b of a non-esterified eremophilane, dendryphiellin G ( 8 ), which is isolated too from the above extracts and proves structurally related to the cyclic portion of 5 . Finally, the free, branched C₉-carboxylic acids dendryphiellic acid A ((+)- 9 ) and B ((+)- 10 ) which correspond to side chains of the above esterified terpenes are also isolated from the above extracts.     

Carbon-nitrogen bond formation in the reaction of the reaction of diphenyl diazomethane Ph2 CN2 with diiron-carbene complexes (Fe2(CO)7x03BD;-C(R)C(NEt2)x03BD;-C(R)C(NEtx03BC;-C(R)C(NEt2)N(NCPh2)x03BC;-C(R)C(NEtx03BC;-C(R)C(NEt2)NN(CPh2)x03BC;-C(R)C(NEt)]

The diiron ynamine complex [Fe₂(CO)₇{μ-CR)C(NEt₂)}] (1:R=Me,2:R = C₃H₅.3:R=SiMe₃.4:R = Ph) reacts at room temperature with diphenyldiazomethane Ph₂CN₂, in hexane to yield complexes [Fe₂(CO)₆{C(R)C(NEt₂)N (NCPh₂)] (5a:R=Me,6a:R=C₃H₅.7a R=SiMe₃.8a:R=Ph) resulting from the insertion of the terminal nitrogen atom into the Fe=C carbene bond. Insertion the second nitrogen atom and formation of compounds [Fe₂(CO)₆zμ-C(R)C(NEt₂)NN(CPh₂)}] (5b:R=Me,6b:R=C₃H₅,7b:R=SiMe₃,8b:R=Ph) is observed when compounds5a-5a are treated in refluxing hexane. Transformation of compoundsa tob is also obtained at room temperature within a few days. All compounds were identified by their¹H NMR spectra. Compounds6a, 7a, 8a, and8b were characterized by single crystal X-ray diffraction analyses. Crystal data: for6a: space group = P2₁/n,a=12.853(1) A,b=24.800(7) A,c=8.947(6) A,β=99.29(3)°,Z=4, 2227 rellectionsR=0,038; for7a: space group=Pl,a=ll.483(4) A,b=14.975(4) A,c = 17.890(8) A,α = 82.80(3)°,β=94.29(7)°,γ=85.42(2),Z = 4, 5888 reflectionR = 0.035: for8a: space group = Pcab.a = 31.023(8) A.b=20.137(1) A.c=9.686(2) A.Z=8. 1651 reflections,R=0.071; for8b: space group=P2₁/n,a=21.459(4),b=10,100(3) A,c=28,439(8) A,ß=103.86(4)°,Z=8. 2431 reflections.R=0.057.     

Modulating the preferred O—H...O hydrogen‐bonding motif in a conformationally constrained environment through hydroxy‐group derivatization

The crystal structures of three conformationally locked esters, namely the centrosymmetric tetrabenzoate of all‐axial perhydronaphthalene‐2,3,4a,6,7,8a‐hexaol, viz.trans‐4a,8a‐dihydroxyperhydronaphthalene‐2,3,6,7‐tetrayl tetrabenzoate, C₃₈H₃₄O₁₀, and the diacetate and dibenzoate of all‐axial perhydronaphthalene‐2,3,4a,8a‐tetraol, viz. (2R*,3R*,4aS*,8aS*)‐4a,8a‐dihydroxyperhydronaphthalene‐2,3‐diyl diacetate, C₁₄H₂₂O₆, and (2R*,3R*,4aS*,8aS*)‐4a,8a‐dihydroxyperhydronaphthalene‐2,3‐diyl dibenzoate, C₂₄H₂₆O₆, have been analyzed in order to examine the preference of their supramolecular assemblies towards competing inter‐ and intramolecular O—H...O hydrogen bonds. It was anticipated that the supramolecular assembly of the esters under study would adopt two principal hydrogen‐bonding modes, namely one that employs intermolecular O—H...O hydrogen bonds (mode 1) and another that sacrifices those for intramolecular O—H...O hydrogen bonds and settles for a crystal packing dictated by weak intermolecular interactions alone (mode 2). Thus, while the molecular assembly of the two crystalline diacyl derivatives conformed to a combination of hydrogen‐bonding modes 1 and 2, the crystal packing in the tetrabenzoate preferred to follow mode 2 exclusively.     

A novel glyceryl ester (glyceryl dendryphiellate A), a trinor-eremophilane (dendryphiellin A1), and eremophilanes (dendryphiellin E1 and E2) from the marine deuteromycete Dendryphiella salina (SUTHERLAND) PUGH et NICOT

Continuing studies of the global extracts from cultures of the marine deuteromycete Dendryphiella salina have led to the isolation of novel compounds that add to the scarce list of marine fungal metabolites. Besides (22E)-ergosta-4.6,8(14),22-tetraen-3-one which, though known from basidiomycetes, was unknown in the sea, they are an unusual glyceryl ester, i.e. glycer-1-yl dendryphiellale A (= (+)-(2R)-2,3-dihydroxyprop-l-yl (6S,2E,4E)6-methylocta-2,4-dienoate; (+)- 1 ), a trinor-eremophilane, i.e. dendryphiellin A1 ( = (+)-(3R*,4E,6E)-7-{[(1R*,2S*,7R*,8aR*)-1,2,6,7,8,8a-hexahydro-7-hydroxy-1,8a-dimethyl-6-oxonaphthalen-2yl]oxycarbonyl}-3-methylhepta-4,6-dienoic acid; (+)- 11 ), and two eremophilanes, i.e. dendryphiellin El ( = (+)-(1R*, 2S*, 7S*,8aR*)-1,2,6,7,8,8a-hexahydro-1,8a-dimethyl-7-(1-methylethenyl)-6-oxonaphthalen-2-yl(6S,2E,4E)-6-methyl-octa-2,4-dienoate; (+)- 13 ) and dendryphiellin E2 ( = (+)-(1R*, 2S*, 8aR*)-1,2,6,7,8,8a-hexahydro-7-isopropyl-idene-1,8a-dimethyl-6-oxonaphthalen-2-yl (6S,2E,4E)-6-Methylocta-2,4-dienoate; (+)- 14 ). Absolute configurations have been established for (+)- 1 via total synthesis and for the acid portion of (+)- 13 and (+)- 14 via transesterification in NaOMe/MeOH which gave in both cases melhyl dendryphiellate A ((+)- 16 ) of known configuration and the free alcoholic moiety of (+)- 14 , i.e. (+)- 17 .     

Stereochemical Course of the Formation of the C(7)‐Formyl Group from a Chiral Methyl Group during the Transformation of Chlorophyllide a into Chlorophyllide b

The biosynthesis of chlorophyll a and chlorophyll b from (2R,3R)‐ and (2S,3S)‐5‐amino[2,3‐¹⁴C₂,2,3‐²H₂,2,3‐³H₂]levulinic acid in greening barley has established that chlorophyllide a oxidase catalyses the transformation of the methyl group at C(7) of chlorophyllide a into the CHO group of chlorophyllide b with the loss of H^Si from the 7‐(hydroxymethyl)chlorophyllide intermediate.     

A tetrahydropentaleno[1,6a‐a]naphthalen‐4(2H)‐one of defined relative stereochemistry for use towards Agariblazeispirol C

Towards the synthesis of the novel natural product Agariblazeispirol C, (5aR*,11bR*)‐9‐methoxy‐3,8,11b‐trimethyl‐5,6,7,11b‐tetrahydro‐1H‐pentaleno[1,6a‐a]naphthalen‐4(2H)‐one, C₂₀H₂₄O₂, has been prepared at a key stage of the preparative programme. The structure shows the desired stereochemical outcome of the central cyclization protocol, viz. a syn‐relationship between the aliphatic methyl group on the 11b‐position and the methylene group on the 5a‐position [C—C—C—C = −34.57 (18)°].     

d- and l-Serine, useful synthons for the synthesis of 24-hydroxyvitamin D3 metabolites. A formal synthesis of 1α,24R,25-(OH)3-D3, 24R,25-(OH)2-D3 and 24S,25-(OH)2-D3

d- and l-Serine have been used for the enantioselective synthesis of tosylates 7a and 7b, useful building blocks for the synthesis of triols 5a and 5b which have already been obtained via a diastereoselective synthesis and used for the synthesis of 2a, 2b and 2c. We have thus performed a formal synthesis of 24S,25-(OH)₂-D₃, 24R,25-(OH)₂-D₃ and 1α,24R,25-(OH)₃-D₃.     

Samaderin B and C from Samadera indica

Samaderin B, or (1R,2S,5R,5aR,7aS,11S,11aS,11bR,14S)‐1,7,7a,11,11a,11b‐hexa­hydro‐1,11‐di­hydroxy‐8,11a,14‐tri­methyl‐2H‐5a,2,5‐(methan­oxy­metheno)­naphth­[1,2‐d]­oxepine‐4,6,10(5H)‐trione, C₁₉H₂₂O₇, and samaderin C, or (1R,2S,5R,5aR,7aS,10S,11S,11aS,11bR,14S)‐7,7a,10,11,11a,11b‐hexa­hydro‐1,10,11‐tri­hydroxy‐8,11a,14‐tri­methyl‐2H‐5a,2,5‐(methan­oxy­metheno)­naphth­[1,2‐d]­oxepine‐4,6(1H,5H)‐dione, C₁₉H₂₄O₇, were isolated from the seed kernels of Samadera indica and were shown to exhibit antifeedant activity against Spodoptera litura third‐instar larvae. The replacement of the carbonyl group in samaderin B by a hydroxy group in samaderin C causes conformational changes at the substitution site, but the overall conformation is not affected; however, the compounds pack differently in the crystal lattice.     

Three ginkgolide hydrates from Ginkgo biloba L.: ginkgolide A monohydrate,ginkgolide C sesquihydrate and ginkgolide J dihydrate,all determined at 120 K

A low‐temperature structure of ginkgolide A monohydrate, (1R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐dimethylethyl)‐hexa­hydro‐4,7b‐di­hydroxy‐8‐methyl‐9H‐1,7a‐epoxymethano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclopenta­[1,2‐d]­furan‐5,9,12(4H)‐trione monohydrate, C₂₀H₂₄O₉·H₂O, obtained from Mo Kα data, is a factor of three more precise than the previous room‐temperature determination. A refinement of the ginkgolide A monohydrate structure with Cu Kα data has allowed the assignment of the absolute configuration of the series of compounds. Ginkgolide C sesquihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11S,11aR)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b,11‐tetrahydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclopenta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione sesquihydrate, C₂₀H₂₄O₁₁·1.5H₂O, has two independent diterpene mol­ecules, both of which exhibit intramolecular hydrogen bonding between OH groups. Ginkgolide J dihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b‐tri­hydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]furo[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione dihydrate, C₂₀H₂₄O₁₀·2H₂O, has the same basic skeleton as the other ginkgolides, with its three OH groups having the same configurations as those in ginkgolide C. The conformations of the six five‐membered rings are quite similar across ­ginkgolides A–C and J, except for the A and F rings of ginkgolide A.