New Eremophilane Sesquiterpenes from a Rhizome Extract of Petasites hybridus

A total of 21 natural products, 1 – 21 , were isolated from a supercritical CO₂ extract of the rhizomes of Petasites hybridus. Thereby, seven new eremophilane (= (1S,4aR,7R,8aR)‐decahydro‐1,8a‐dimethyl‐7‐(1‐methylethyl)naphthalene) sesquiterpenes, compounds 4, 5, 9, 11, 12, 15 , and 17 , were identified. The new constituent 9‐hydroxyisobakkenolide ( 15 ) is the first representative of a group of compounds closely related to the well‐known, but rare, bakkenolides. Tsoongianolide B ( 18 ) and its degradation product ligularenolide ( 19 ) were found as new Petasites constituents as well. The known eremophilanolide 2 was isolated from a plant source for the first time and the oxofuranopetasin 16 was isolated for the first time from the rhizomes of P. hybridus, together with eight other known compounds. The C(8)‐epimeric 2‐[(tigloyl)oxy]eremophilanolides 3 and 8 could clearly be differentiated. All structures were established by extensive 1D‐ and 2D‐NMR experiments (Tables 1–3), and confirmed by in‐depth GC/MS and HPLC/MS experiments.     

New Antifungal `Quinone Methide' Diterpenes from Bobgunnia madagascariensis and Study of Their Interconversion by LC/NMR

Two new `quinone methide' diterpenes with a cassane skeleton were isolated from the root bark of Bobgunnia madagascariensis (Desv. ) J. H. Kirkbr. & Wiersema (Leguminosae). The two compounds occurred as a diastereoisomer mixture 1 / 2 . Their structure was established as (4R,6aS,10aS)‐ and (4S,6aS,10aS)‐ 1,4,6a,7,8,9,10,10a‐octahydro‐4,11‐dihydroxy‐7,7,10a‐trimethyl‐2H‐phenanthro[1,2‐c]pyran‐6,12‐dione by spectroscopic methods and by comparison with the data obtained for another `quinone methide' diterpene isolated previously from the same plant and identified by single‐crystal X‐ray analysis. ¹H‐ and ¹³C‐NMR signals were assigned by extensive in‐mixture 2D correlation experiments, and ¹H‐NMR spectra of the separated diastereoisomers 1 and 2 were recorded by on‐flow LC/NMR. The interconversion of 1 and 2 was followed by repeated stop‐flow LC/NMR experiments over a two‐hour period. Compounds 1 and 2 showed moderate antifungal properties towards human pathogenic fungi, in particular the yeast Candida albicans.     

Terpenoids from Croton regelianus

Two new terpenoids, the bisnorditerpene rel‐(5β,8α,10α)‐8‐hydroxy‐13‐methylpodocarpa‐9(11),13‐diene‐3,12‐dione ( 1 ) and the guaiane sesquiterpene rel‐(1R,4S,6R,7S,8aR)‐decahydro‐1‐(hydroxymethyl)‐4,9,9‐trimethyl‐4,7‐(epoxymethano)azulen‐6‐ol ( 2 ), together with seven known compounds, were isolated from Croton regelianus var. matosii. The structures of the isolated compounds were determined by HR‐ESI‐TOF and a combination of 1D‐ and 2D‐NMR experiments.     

Two New Highly Oxidized Humulane Sesquiterpenes from the Basidiomycete Lactarius mitissimus

Two new highly oxidized humulane sesquiterpenes, mitissimols F ( 1 ) and G ( 2 ), were isolated from the fruiting bodies of Lactarius mitissimus. Their structures were elucidated by using extensive spectroscopic techniques including 1D‐ and 2D‐NMR experiments. The absolute configuration of mitissimol F ( 1 ) was determined by ¹H‐NMR resolution of its diastereoisomeric α‐methoxy‐α‐(trifluoromethyl)benzeneacetates (MTPA). It was shown to be (1S,3E,6S,8R,9R,10S,11R)‐8,9 : 10,11‐diepoxy‐1,6‐dihydroxyhumul‐3‐en‐5‐one (=(1S,2R,4R,6S,8E,11S,12R)‐6,11‐dihydroxy‐1,6,10,10‐tetramethyl‐3,13‐dioxatricyclo[10.1.0.0^2,4]tridec‐8‐en‐7‐one).     

Unexpected Novel Pheophytin Peroxides from the Leaves of Biden pilosa

Two new pheophytins, bidenphytins A ( 1 ) and B ( 2 ), with peroxide functionalities on ring E, were isolated from Biden pilosa Linn . var. radiata Sch . Bip ., a popular Taiwanese folk medicine. Also isolated were the following six known compounds: pheophytin a ( 3 ), (13²R)‐13²‐hydroxypheophytin a ( 4 ), (13²S)‐13²‐hydroxypheophytin a ( 5 ), (13²R)‐13²‐hydroxypheophytin b ( 6 ), (13²S)‐13²‐hydroxypheophytin b ( 7 ), and aristophyll‐C ( 8 ). Their structures were elucidated by spectroscopic methods (UV, IR, 1D‐ and 2D‐NMR) and by mass spectrometry (HR‐FAB‐MS). Possible biosynthetic pathways for 1 and 2 are proposed.     

Synthesis,Structure, and Conformation of 2′,3′‐Fused Oxathiane and Thiomorpholine Uridines

The syntheses of two 2′,3′‐fused bicyclic nucleoside analogues, i.e., 1‐[(4aR,5R,7R,7aS)‐hexahydro‐5‐(hydroxymethyl)‐4,4‐dioxidofuro[3,4‐b][1,4]oxathiin‐7‐yl]pyrimidine‐2,4(1H,3H)‐dione ( 1a ) and 1‐[(4aS,5R,7R,7aS)‐hexahydro‐7‐(hydroxymethyl)‐1,1‐dioxido‐2H‐furo[3,4‐b][1,4]thiazin‐5‐yl]pyrimidine‐ 2,4(1H,3H)‐dione ( 1b ), are described, the key step being an intramolecular hetero‐Michael addition. Their structures and conformations, previously solved by X‐ray crystallography, were analyzed in more detail, using 1D‐ and 2D‐NMR as well as HR‐MS analyses.     

A Lignoid Glycoside and Dimeric Phenylpropanoids from Daphne oleoides

Three new natural products, a lignoid glycoside 1 and two dimeric phenylpropanoids 2 and 3 , along with two known lignans 4 and 5 , were isolated from the BuOH‐ and CHCl₃‐soluble fractions of the whole plant of Daphne oleoides (Thymelaeaceae). The structures of the new compounds were established by spectroscopic techniques, including 2D NMR, as 4‐(β‐D ‐glucopyranosyloxy)‐9′‐hydroxy‐3,3′,4′‐trimethoxy‐7′,9‐epoxylignan ( 1 ), (1R,2S,5R,6R)‐6‐(3‐ethyl‐4‐hydroxy‐5‐methoxyphenyl)‐2‐(4‐hydroxy‐3,5‐dimethoxyphenyl)‐3,7‐dioxabicyclo[3.3.0]octane ( 2 ) and (1R,2S,5R,6S)‐2,6‐bis(3‐ethyl‐4‐hydroxy‐5‐methoxyphenyl)‐3,7‐dioxabicyclo[3.3.0]octane ( 3 ). The other lignans were identified as (+)‐pinoresinol O‐(β‐D ‐glucopyranoside) ( 4 ) and (+)‐medioresinol ( 5 ).     

Three New Diterpenoids from Rabdosia lophanthoides var. gerardiana

Three new diterpenoids, together with three known ones, were isolated from the air‐dried whole herbs of Rabdosia lophanthoides var. gerardiana. The structures of the new diterpenoids were established as 3,4‐dihydro‐11‐hydroxy‐10‐(1‐hydroxy‐1‐methylethyl)‐2,2,6‐trimethylnaphtho[1,8‐bc]oxocin‐5(2H)‐one ( 1 ), 11,12,15‐trihydroxyabieta‐5,8,11,13‐tetraen‐7‐one ( 2 ), (2R,3S,4S,4aR,8S,9aS,13aS,16aS)‐3,4,4a,8,9,9a,10,11,12,13,14,16a‐dodecahydro‐2‐(hydroxymethyl)‐6,6,10,10‐tetramethyl‐2H‐benzo[4,5]cyclohepta[1,2‐h]pyrano[2,3‐b][1,4]benzodioxepine‐3,4,8,13a,15(6H)‐pentol ( 3 ) by spectroscopic methods, including extensive 1D‐ and 2D‐NMR analyses. The structures of the known compounds were identified by comparison of their physical and spectroscopic data with those reported in the literature.     

Cadinene Derivatives from Eupatorium adenophorum

A new norsesquiterpene named eupatorone (= (4S,4aR,6R)‐1‐acetyl‐6‐(acetyloxy)‐4,4a,5,6‐tetrahydro‐4,7‐dimethylnaphthalen‐2(3H)‐one; 1 ) and a new sesquiterpene derivative named 2‐deoxo‐2‐(acetyloxy)‐9‐oxoageraphorone (= (1R,4S,4aR,6R,8aS)‐6‐(acetyloxy)‐3,4,4a,5,6,8a‐hexahydro‐4,7‐dimethyl‐1‐(1‐methylethyl)naphthalen‐2(1H)‐one; 2 ), together with the five known cadinene derivatives 3 – 7 were isolated from the flower of Eupatorium adenophorum (Spreng. ). Their structures were established by extensive NMR experiments, including 1D and 2D NMR.     

A New Alkaloid from the Seeds of Sophora alopecuroides L.

Alopecurin A, an alkaloid with an unprecedented skeleton, was isolated from the seeds of Sophora alopecuroides L. The absolute configuration and structure of this compound was identified as (3S,12R)‐3‐hydroxy‐1,7‐diazatricyclo[10.4.0.1^3,7]heptadecane‐11,16,17‐trione (=(7S,15aR)‐decahydro‐7‐hydroxy‐6H‐7,11‐methano‐4H‐pyrido[1,2‐a][1,7]diazacyclododecine‐4,15,16(12H)‐trione). The structure and absolute configuration was elucidated by spectroscopic methods, mainly HR‐ESI‐TOF‐MS, IR, 1D‐NMR (¹H‐ and ¹³C‐NMR), 2D‐NMR (COSY, NOESY, HSQC, HMBC), and particularly X‐ray crystal‐diffraction and CD spectral analysis.     

Metabolism of Deuterated threo‐Dihydroxy Fatty Acids in Saccharomyces cerevisiae: Enantioselective Formation and Characterization of Hydroxylactones and γ‐Lactones

Biotransformation of (±)‐threo‐7,8‐dihydroxy(7,8‐²H₂)tetradecanoic acids (threo‐(7,8‐²H₂)‐ 3 ) in Saccharomyces cerevisiae afforded 5,6‐dihydroxy(5,6‐²H₂)dodecanoic acids (threo‐(5,6‐²H₂)‐ 4 ), which were converted to (5S,6S)‐6‐hydroxy(5,6‐²H₂)dodecano‐5‐lactone ((5S,6S)‐(5,6‐²H₂)‐ 7 ) with 80% e.e. and (5S,6S)‐5‐hydroxy(5,6‐²H₂)dodecano‐6‐lactone ((5S,6S)‐5,6‐²H₂)‐ 8 ). Further β‐oxidation of threo‐(5,6‐²H₂)‐ 4 yielded 3,4‐dihydroxy(3,4‐²H₂)decanoic acids (threo‐(3,4‐²H₂)‐ 5 ), which were converted to (3R,4R)‐3‐hydroxy(3,4‐²H₂)decano‐4‐lactone ((3R,4R)‐ 9 ) with 44% e.e. and converted to ²H‐labeled decano‐4‐lactones ((4R)‐(3‐²H₁)‐ and (4R)‐(2,3‐²H₂)‐ 6 ) with 96% e.e. These results were confirmed by experiments in which (±)‐threo‐3,4‐dihydroxy(3,4‐²H₂)decanoic acids (threo‐(3,4‐²H₂)‐ 5 ) were incubated with yeast. From incubations of methyl (5S,6S)‐ and (5R,6R)‐5,6‐dihydroxy(5,6‐²H₂)dodecanoates ((5S,6S)‐ and (5R,6R)‐(5,6‐²H₂)‐ 4a ), the (5S,6S)‐enantiomer was identified as the precursor of (4R)‐(3‐²H₁)‐ and (2,3‐²H₂)‐ 6 ). Therefore, (4R)‐ 6 is synthesized from (3S,4S)‐ 5 by an oxidation/keto acid reduction pathway involving hydrogen transfer from C(4) to C(2). In an analogous experiment, methyl (9S,10S)‐9,10‐dihydroxyoctadecanoate ((9S,10S)‐ 10a ) was metabolized to (3S,4S)‐3,4‐dihydroxydodecanoic acid ((3S,4S)‐ 15 ) and converted to (4R)‐dodecano‐4‐lactone ((4R)‐ 18 ).     

Determination of Absolute Configuration of Decipinone,a Diterpenoid Ester with a Myrsinane‐Type Carbon Skeleton,by NMR Spectroscopy

The absolute configuration of decipinone ( 2 ), a myrsinane‐type diterpene ester previously isolated from Euphorbia decipiens, has been determined by NMR study of its axially chiral derivatives (aR)‐ and (aS)‐N‐hydroxy‐2′‐methoxy‐1,1′‐binaphthalene‐2‐carboximidoyl chloride ((aR)‐MBCC ( 3a ) and (aS)‐MBCC ( 3b )). The absolute configurations at C(7) and C(13) of 2 determined were (R) and (S), respectively. Therefore, considering the relative configuration of 2 , the absolute configuration determined was (2S,3S,4R,5R,6R,7R,11S,12R,13S,15R).     

Asymmetric Syntheses of New Polyhydroxylated Quinolizidines: Cross‐Aldol Reactions of 7‐Oxabicyclo[2.2.1]heptan‐2‐one and 3a,4a,7a,7b‐Tetrahydro[1,3]dioxolo[4,5]furo[2,3‐d]isoxazole‐3‐carbaldehyde Derivatives

The cross‐aldolization of (−)‐(1S,4R,5R,6R)‐6‐endo‐chloro‐5‐exo‐(phenylseleno)‐7‐oxabicyclo[2.2.1]heptan‐2‐one ((−)‐ 25 ) and of (+)‐(3aR,4aR,7aR,7bS)‐ ((+)‐ 26 ) and (−)‐(3aS,4aS,7aS,7bR)‐3a,4a,7a,7b‐tetrahydro‐6,6‐dimethyl[1,3]dioxolo[4,5]furo[2,3‐d]isoxazole‐3‐carbaldehyde ((−)‐ 26 ) was studied for the lithium enolate of (−)‐ 25 and for its trimethylsilyl ether (−)‐ 31 under Mukaiyama's conditions (Scheme 2). Protocols were found for highly diastereoselective condensation giving the four possible aldols (+)‐ 27 (`anti'), (+)‐ 28 (`syn'), 29 (`anti'), and (−)‐ 30 (`syn') resulting from the exclusive exo‐face reaction of the bicyclic lithium enolate of (−)‐ 25 and bicyclic silyl ether (−)‐ 31 . Steric factors can explain the selectivities observed. Aldols (+)‐ 27 , (+)‐ 28 , 29 , and (−)‐ 30 were converted stereoselectively to (+)‐1,4‐anhydro‐3‐{(S)‐[(tert‐butyl)dimethylsilyloxy][(3aR,4aR,7aR,7bS)‐3a,4a,7a,7b‐tetrahydro‐6,6‐dimethyl[1,3]dioxolo[4,5]‐furo[2,3‐d]isoxazol‐3‐yl]methyl}‐3‐deoxy‐2,6‐di‐O‐(methoxymethyl)‐α‐D ‐galactopyranose ((+)‐ 62 ), its epimer at the exocyclic position (+)‐ 70 , (−)‐1,4‐anhydro‐3‐{(S)‐[(tert‐butyl)dimethylsilyloxy][(3aS,4aS,7aS,7bR)‐3a,4a,7a,7b‐tetrahydro‐6,6‐dimethyl[1,3]dioxolo[4,5]furo[2,3‐d]isoxazol‐3‐yl]methyl}‐3‐deoxy‐2,6‐di‐O‐(methoxymethyl)‐α‐D ‐galactopyranose ((−)‐ 77 ), and its epimer at the exocyclic position (+)‐ 84 , respectively (Schemes 3 and 5). Compounds (+)‐ 62 , (−)‐ 77 , and (+)‐ 84 were transformed to (1R,2R,3S,7R,8S,9S,9aS)‐1,3,4,6,7,8,9,9a‐octahydro‐8‐[(1R,2R)‐1,2,3‐trihydroxypropyl]‐2H‐quinolizine‐1,2,3,7,9‐pentol ( 21 ), its (1S,2S,3R,7R,8S,9S,9aR) stereoisomer (−)‐ 22 , and to its (1S,2S,3R,7R,8S,9R,9aR) stereoisomer (+)‐ 23 , respectively (Schemes 6 and 7). The polyhydroxylated quinolizidines (−)‐ 22 and (+)‐ 23 adopt `trans‐azadecalin' structures with chair/chair conformations in which H−C(9a) occupies an axial position anti‐periplanar to the amine lone electron pair. Quinolizidines 21 , (−)‐ 22 , and (+)‐ 23 were tested for their inhibitory activities toward 25 commercially available glycohydrolases. Compound 21 is a weak inhibitor of β‐galactosidase from jack bean, of amyloglucosidase from Aspergillus niger, and of β‐glucosidase from Caldocellum saccharolyticum. Stereoisomers (−)‐ 22 and (+)‐ 23 are weak but more selective inhibitors of β‐galactosidase from jack bean.     

Asymmetric Synthesis of Complicated Bicyclic and Tricyclic Polypropanoates via the Double Diels‐Alder Addition of 2,2′‐Ethylidenebis[3,5‐dimethylfuran]

A new, non‐iterative method for the asymmetric synthesis of long‐chain and polycyclic polypropanoate fragments starting from 2,2′‐ethylidenebis[3,5‐dimethylfuran] ( 2 ) has been developed. Diethyl (2E,5E)‐4‐oxohepta‐2,5‐dienoate ( 6 ) added to 2 to give a single meso‐adduct 7 containing nine stereogenic centers. Its desymmetrization was realized by hydroboration with (+)‐IpcBH₂ (isopinocampheylborane), leading to diethyl (1S,2R,3S,4S,4aS,7R,8R,8aR,9aS,10R,10aR)‐1,3,4,7,8,8a,9,9a‐octahydro‐3‐hydroxy‐2,4,5,7,10‐pentamethyl‐9‐oxo‐2H,10H‐2,4a : 7,10a‐diepoxyanthracene‐1,8‐dicarboxylate ((+)‐ 8 ; 78% e.e.). Alternatively, 7 was converted to meso‐(1R,2R,4R,4aR,5S,7S,8S,8aR,9aS,10s,10aS)‐1,8‐bis(acetoxymethyl)‐1,8,8a,9a‐tetrahydro‐2,4,5,7,10‐pentamethyl‐2H‐10H‐2,4a : 7,10a‐diepoxyanthracene‐3,6,9(4H,5H,7H)‐trione ( 32 ) that was reduced enantioselectively by BH₃ catalyzed by methyloxazaborolidine 19 derived from L ‐diphenylprolinol giving (1S,2S,4S,4aS,5S,6R,7R,8R,8aS,9aR,10R,10aS)‐1,8‐bis(acetoxymethyl)‐1,8,8a,9a‐tetrahydro‐6‐hydroxy‐2,4,5,7,10‐pentamethyl‐2H,10H‐2,4a : 7,10a‐diepoxyanthracene‐3,9(4H,7H)‐dione ((−)‐ 33 ; 90% e.e.). Chemistry was explored to carry out chemoselective 7‐oxabicyclo[2.2.1]heptanone oxa‐ring openings and intra‐ring C−C bond cleavage. Polycyclic polypropanoates such as (1R,2S,3R,4R,4aR,5S,6R,7S,8R,9R,10R,11S,12aR)‐1‐(ethoxycarbonyl)‐1,3,4,7,8,9,10,11,12,12a‐decahydro‐3,11‐dihydroxy‐2,4,5,7,9‐pentamethyl‐12‐oxo‐2H,5H‐2,4a : 6,9 : 6,11‐triepoxybenzocyclodecene‐10,8‐carbolactone ( 51 ), (1S,2R,3R,4R,4aS,5S,7S,8R,9R,10R,12S,12aS)‐1,10‐bis(acetoxymethyl)tetradecahydro‐8‐(methoxymethoxy)‐2,4,5,7,9‐pentamethyl‐3,9‐bis{[2‐(trimethylsilyl)ethoxy]methoxy}‐6,11‐epoxycyclodecene‐4a,6,11,12‐tetrol ((+)‐ 83 ), and (1R,2R,3R,4aR,4bR,5S,6R, 7R,8R,8aS,9S,10aR)‐3,5‐bis(acetoxymethyl)‐4a,8a‐dihydroxy‐1‐(methoxymethoxy)‐2,6,8,9,10a‐pentamethyl‐2,7‐bis{[2‐(trimethylsilyl)ethoxy]methoxy}dodecahydrophenanthrene‐4,10‐dione ( 85 ) were obtained in few synthetic steps.     

Metabolism of Deuterated erythro‐Dihydroxy Fatty Acids in Saccharomyces cerevisiae: Enantioselective Formation and Characterization of Hydroxylactones

Epoxides of fatty acids are hydrolyzed by epoxide hydrolases (EHs) into dihydroxy fatty acids which are of particular interest in the mammalian leukotriene pathway. In the present report, the analysis of the configuration of dihydroxy fatty acids via their respective hydroxylactones is described. In addition, the biotransformation of (±)‐erythro‐7,8‐ and ‐3,4‐dihydroxy fatty acids in the yeast Saccharomyces cerevisiae was characterized by GC/EI‐MS analysis. Biotransformation of chemically synthesized (±)‐erythro‐7,8‐dihydroxy(7,8‐²H₂)tetradecanoic acid ((±)‐erythro‐ 1 ) in the yeast S. cerevisiae resulted in the formation of 5,6‐dihydroxy(5,6‐²H₂)dodecanoic acid ( 6 ), which was lactonized into (5S,6R)‐6‐hydroxy(5,6‐²H₂)dodecano‐5‐lactone ((5S,6R)‐ 4 ) with 86% ee and into erythro‐5‐hydroxy(5,6‐²H₂)dodecano‐6‐lactone (erythro‐ 8 ). Additionally, the α‐ketols 7‐hydroxy‐8‐oxo(7‐²H₁)tetradecanoic acid ( 9a ) and 8‐hydroxy‐7‐oxo(8‐²H₁)tetradecanoic acid ( 9b ) were detected as intermediates. Further metabolism of 6 led to 3,4‐dihydroxy(3,4‐²H₂)decanoic acid ( 2 ) which was lactonized into 3‐hydroxy(3,4‐²H₂)decano‐4‐lactone ( 5 ) with (3R,4S)‐ 5 =88% ee. Chemical synthesis and incubation of (±)‐erythro‐3,4‐dihydroxy(3,4‐²H₂)decanoic acid ((±)‐erythro‐ 2 ) in yeast led to (3S,4R)‐ 5 with 10% ee. No decano‐4‐lactone was formed from the precursors 1 or 2 by yeast. The enantiomers (3S,4R)‐ and (3R,4S)‐3,4‐dihydroxy(3‐²H₁)nonanoic acid ((3S,4R)‐ and (3R,4S)‐ 3 ) were chemically synthesized and comparably degraded by yeast without formation of nonano‐4‐lactone. The major products of the transformation of (3S,4R)‐ and (3R,4S)‐ 3 were (3S,4R)‐ and (3R,4S)‐3‐hydroxy(3‐²H₁)nonano‐4‐lactones ((3S,4R)‐ and (3R,4S)‐ 7 ), respectively. The enantiomers of the hydroxylactones 4, 5 , and 7 were chemically synthesized and their GC‐elution sequence on Lipodex^® E chiral phase was determined.     

Preparation and (E/Z)‐Isomerization of the Diastereoisomers of Violaxanthin

Violaxanthin A (=(all‐E,3S,5S,6R,3′S,5′S,6′R)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol =syn,syn‐violaxanthin; 5 ) and violaxanthin B (=(all‐E,3S,5S,6R,3′S,5′R,6′S)‐5,6 : 5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene‐3,3′‐diol=syn,anti‐violaxanthin; 6 ) were prepared by epoxidation of zeaxanthin diacetate ( 1 ) with monoperphthalic acid. Violaxanthins 5 and 6 were submitted to thermal isomerization and I₂‐catalyzed photoisomerization. The structure of the main products, i.e., (9Z)‐ 5 , (13Z)‐ 5 , (9Z)‐ 6 , (9′Z)‐ 6 , (13Z)‐ 6 , and (13′Z)‐ 6 , was determined by their UV/VIS, CD, ¹H‐NMR, ¹³C‐NMR, and mass spectra.     

Metabolism of Deuterated Isomeric 6,7‐Dihydroxydodecanoic Acids in Saccharomyces cerevisiae – Diastereo‐ and Enantioselective Formation and Characterization of 5‐Hydroxydecano‐4‐lactone (=4,5‐Dihydro‐5‐(1‐hydroxyhexyl)furan‐2(3H)‐one) Isomers

The chemical synthesis of deuterated isomeric 6,7‐dihydroxydodecanoic acid methyl esters 1 and the subsequent metabolism of esters 1 and the corresponding acids 1a in liquid cultures of the yeast Saccharomyces cerevisiae was investigated. Incubation experiments with (6R,7R)‐ or (6S,7S)‐6,7‐dihydroxy(6,7‐²H₂)dodecanoic acid methyl ester ((6R,7R)‐ or (6S,7S)‐(6,7‐²H₂)‐ 1 , resp.) and (±)‐threo‐ or (±)‐erythro‐6,7‐dihydroxy(6,7‐²H₂)dodecanoic acid ((±)‐threo‐ or (±)‐erythro‐(6,7‐²H₂)‐ 1a , resp.) elucidated their metabolic pathway in yeast (Tables 1–3). The main products were isomeric ²H‐labeled 5‐hydroxydecano‐4‐lactones 2 . The absolute configuration of the four isomeric lactones 2 was assigned by chemical synthesis via Sharpless asymmetric dihydroxylation and chiral gas chromatography (Lipodex ^® E). The enantiomers of threo‐ 2 were separated without derivatization on Lipodex ^® E; in contrast, the enantiomers of erythro‐ 2 could be separated only after transformation to their 5‐O‐(trifluoroacetyl) derivatives. Biotransformation of the methyl ester (6R,7R)‐(6,7‐²H₂)‐ 1 led to (4R,5R)‐ and (4S,5R)‐(2,5‐²H₂)‐ 2 (ratio ca. 4 : 1; Table 2). Estimation of the label content and position of (4S,5R)‐(2,5‐²H₂)‐ 2 showed 95% label at C(5), 68% label at C(2), and no ²H at C(4) (Table 2). Therefore, oxidation and subsequent reduction with inversion at C(4) of 4,5‐dihydroxydecanoic acid and transfer of ²H from C(4) to C(2) is postulated. The 5‐hydroxydecano‐4‐lactones 2 are of biochemical importance: during the fermentation of Streptomyces griseus, (4S,5R)‐ 2 , known as L‐factor, occurs temporarily before the antibiotic production, and (?)‐muricatacin (=(4R,5R)‐5‐hydroxy‐heptadecano‐4‐lactone), a homologue of (4R,5R)‐ 2 , is an anticancer agent.     

Chiral Heterospirocyclic 2H‐Azirin‐3‐amines as Synthons for 3‐Amino‐2,3,4,5‐tetrahydrofuran‐3‐carboxylic Acid and Their Use in Peptide Synthesis

The heterospirocyclic N‐methyl‐N‐phenyl‐5‐oxa‐1‐azaspiro[2.4]hept‐1‐e n‐2‐amine (6 ) and N‐(5‐oxa‐1‐azaspiro[2.4]hept‐1‐en‐2‐yl)‐(S)‐proline methyl ester ( 7 ) were synthesized from the corresponding heterocyclic thiocarboxamides 12 and 10 , respectively, by consecutive treatment with COCl₂, 1,4‐diazabicyclo[2.2.2]octane, and NaN₃ (Schemes 1 and 2). The reaction of these 2H‐azirin‐3‐amines with thiobenzoic and benzoic acid gave the racemic benzamides 13 and 14 , and the diastereoisomeric mixtures of the N‐benzoyl dipeptides 15 and 16 , respectively (Scheme 3). The latter were separated chromatographically. The configurations and solid‐state conformations of all six benzamides were determined by X‐ray crystallography. With the aim of examining the use of the new synthons in peptide synthesis, the reactions of 7 with Z‐Leu‐Aib‐OH to yield a tetrapeptide 17 (Scheme 4), and of 6 with Z‐Ala‐OH to give a dipeptide 18 (Scheme 5) were performed. The resulting diastereoisomers were separated by means of MPLC or HPLC. NMR Studies of the solvent dependence of the chemical shifts of the NH resonances indicate the presence of an intramolecular H‐bond in 17 . The dipeptides (S,R)‐ 18 and (S,S)‐ 18 were deprotected at the N‐terminus and were converted to the crystalline derivatives (S,R)‐ 19 and (S,S)‐ 19 , respectively, by reaction with 4‐bromobenzoyl chloride (Scheme 5). Selective hydrolysis of (S,R)‐ 18 and (S,S)‐ 18 gave the dipeptide acids (R,S)‐ 20 and (S,S)‐ 20 , respectively. Coupling of a diastereoisomeric mixture of 20 with H‐Phe‐O^tBu led to the tripeptides 21 (Scheme 5). X‐Ray crystal‐structure determinations of (S,R)‐ 19 and (S,S)‐ 19 allowed the determination of the absolute configurations of all diastereoisomers isolated in this series.     

Terpenoids from the Roots of Ligularia muliensis

Three new eremophilane‐type sesquiterpenes, (6β,8α)‐6‐(acetyloxy)‐8‐hydroxyeremophil‐7(11)‐en‐12,8‐olide ( 1 ), (6α,8α)‐6‐hydroxyeremophil‐7(11)‐en‐12,8‐olide ( 2 ), and (6α,8α)‐6‐(acetyloxy)eremophil‐7(11)‐en‐12,8‐olide ( 3 ) ((8α)‐eremophil‐7(11)‐en‐12,8‐olide = (4aR,5S,8aR,9aS)‐4a,5,6,7,8,8a,9,9a‐octahydro‐3,4a,5‐trimethylnaphtho[2,3‐b]furan‐2(4H)‐one), besides the recently elucidated eremoligularin ( 4 ) and bieremoligularolide ( 5 ), as well as a new highly oxygenated monoterpene, rel‐(1R,2R,3R,4S,5S)‐p‐menthane‐1,2,3,5‐tetrol ( 12 ), together with six known constituents, i.e., the sesquiterpenes 6 and 7 , the norsesquiterpenes 8 – 10 , and the monoterpene 13 , were isolated from the roots of Ligularia muliensis. In addition, an attempt to dimerize 1 to a bieremophilenolide (Scheme) resulted in the generation of the new derivative (6β,8β)‐6‐(acetyloxy)‐8‐chloroeremophil‐7(11)‐en‐12,8‐olide ( 11 ). The new structures were established by means of detailed spectroscopic analysis (IR, FAB‐, EI‐, or HR‐ESI‐MS as well as 1D‐ and 2D‐NMR experiments). Compounds 4 and 5 were evaluated for their antitumor effects in vitro (Table 3).     

Characterization of novel isobenzofuranones by DFT calculations and 2D NMR analysis

Phthalides are frequently found in naturally occurring substances and exhibit a broad spectrum of biological activities. In the search for compounds with insecticidal activity, phthalides have been used as versatile building blocks for the syntheses of novel potential agrochemicals. In our work, the Diels–Alder reaction between furan‐2(5H)‐one and cyclopentadiene was used successfully to obtain (3aR,4S,7R,7aS)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aS,4R,7S,7aR)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 2 ) and (3aS,4S,7R,7aR)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aR,4R,7S,7aS)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 3 ). The endo adduct ( 2 ) was brominated to afford (3aR,4R,5R,7R,7aS,8R)‐5,8‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aS,4S,5S,7S,7aR,8S)‐5,8‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 4 ) and (3aS,4R,5R,6S,7S,7aR)‐5,6‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aR,4S,5S,6R,7R,7aS)‐5,6‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 5 ). Following the initial analysis of the NMR spectra and the proposed two novel unforeseen products, we have decided to fully analyze the classical and non‐classical assay structures with the aid of computational calculations. Computation to predict the ¹³C and ¹H chemical shifts for mean absolute error analyses have been carried out by gauge‐including atomic orbital method at M06‐2X/6‐31+G(d,p) and B3LYP/6‐311+G(2d,p) levels of theory for all viable conformers. Characterization of the novel unforeseen compounds ( 4 ) and ( 5 ) were not possible by employing only the experimental NMR data; however, a more conclusive structural identification was performed by comparing the experimental and theoretical ¹H and ¹³C chemical shifts by mean absolute error and DP4 probability analyses. Copyright © 2016 John Wiley & Sons, Ltd.