Salvifarinin A,a neo-clerodane diterpenoid with a 6/5/7 tricyclic skeleton from Salvia farinacea

Salvifarinin A (1), a rearrangement product of Languidulane-type clerodane diterpenoids with a 6/5/7 tricyclic ring skeleton fused with γ-lactone ring and furan ring, and two new biogenetically related diterpernoids, salvifarinins B (2) and C (3), were isolated from the aerial parts of Salvia farinacea. The absolute configuration of 1 was elucidated by extensive spectroscopic methods, and confirmed by single crystal X-ray diffraction and bio-inspired semisynthesis. The plausible biogenetic pathway was also proposed. Compound 2 displayed a potent effect on reducing hepatic steatosis.     

Rhodauricanol A,an analgesic diterpenoid with an unprecedented 5/6/5/7 tetracyclic system featuring a unique 16-oxa-tetracyclo[11.2.1.01,5.07,13]hexadecane core from Rhododendron dauricum

A novel diterpenoid with an unprecedented 5/6/5/7 tetracyclic system, rhodauricanol A (1), five new grayanane-derived diterpenoids, dauricanols A?E (2?6), and five known ones (7?11) were isolated from the flowers of Rhododendron dauricum. Rhodauricanol A (1) possesses a unique 5/6/5/7 tetracyclic ring system featuring a 16-oxa-tetracyclo[11.2.1.0^1,5.0^7,13]hexadecane core. Dauricanols A?C (2?4) are the first 1,3-dioxolane conjugates of grayanane diterpenoids and 5-hydroxymethylfurfural and vanillin, respectively, and dauricanols D (5) and E (6) represent the first examples of 6-deoxy-1,5-seco-grayanane diterpenoids. Their structures were determined by spectroscopic methods, quantum chemical calculation including ¹³C NMR-DP4+ analysis and ECD calculation, and single-crystal X-ray diffraction analysis. Plausible biosynthetic pathways for 1?4 were proposed. All the isolates showed significant analgesic activities, and dauricanols B (3) and C (4) showed more potent analgesic activities than the positive control, morphine.     

Inuroyleanol and 7-ketoroyleanone,two novel diterpenoids of Inula royleana DC

From the roots of Inula royleana DC (Compositae), two novel tricyclic diterpenoids, named inuroyleanol and 7-ketoroyleanone, have been isolated and their structures established. Inuroyleanol is 11,14-dihydroxy-12-methoxy-abieta-8,11,13-trien-7-one (3a) and 7-ketoroyleanone is 12-hydroxy-abieta-8,12-dien-7,11,14-trione (1d). Inuroyleanol provides a link in the series of naturally occurring oxidative metabolites of the ferruginol (2) skeleton.     

Vulgarisins B–D,three novel diterpenoids with a rare skeleton isolated from Prunella vulgaris Linn

Three new diterpenoids, vulgarisins B–D (1–3), have been isolated from a medicinal plant Prunella vulgaris Linn. These diterpenoids contain a rare 5/6/4/5 fused tetracyclic ring skeleton. Their structures were determined through the analysis of spectroscopic data, and the absolute configuration were further confirmed by single crystal X-ray diffraction as well as CD analysis. All the compounds were evaluated for their cytotoxicity activity, vulgarisins B (1) and C (2) demonstrated modest cytotoxicity activity against human lung carcinoma A549 cell line.     

Arnequinol A and arnequinone A,two unique meroterpenoids from Arnebia euchroma

Arnequinol A(1), featuring an unprecedented 6/6/3 tricyclic carbon skeleton fused with a heptatomic oxo-bridge, together with arnequinone A(2) bearing a highly conjugated methyl-shifting benzogeijerene skeleton, were isolated from Arnebia euchroma. Their structures were elucidated by extensive spectroscopic methods and quantum chemical calculations of the13C nuclear magnetic resonance(NMR) data and electronic circular dichroism(ECD) spectra. The plausible biosynthetic pathways for 1 and 2 were p...     

Abietane derived diterpenoids as Cav3.1 antagonists from Salvia digitaloides

Nineteen diterpenoids, including saldigitin A(1) bearing an unprecedented 10-methylated 6/7/6 carbon ring system, two new icetexanes(2, 3), and two new nor-abietanes(5, 6) were characterized from the roots of Salvia digitaloides. Their structures were elucidated by the analysis of the spectroscopic data,X-ray crystallography, and TDDFT calculations of ECD spectra. The novel architecture of 1 should be biogenetically derived through the cleavage and re-cyclization of the B/C rings from the normal...     

Divergent Asymmetric Total Synthesis of Mulinane Diterpenoids

A concise, divergent, asymmetric total syntheses of mulinane diterpenoids has been achieved. Specifically, a new strategy was developed featuring a key intramolecular Friedel–Crafts reaction to construct the chiral fused 5‐6‐6 tricyclic motif, followed by sequential Birch reduction, conjugate methylation, and homologation/ring‐expansion reactions to furnish the desired 5‐6‐7 tricyclic skeleton bearing five contiguous stereocenters. With this efficient strategy, seven mulinane diterpenoids and two analogues were synthesized via late‐stage functional modification or functionalization in 8.6–20 % overall yields and 11–15 steps.     

Stachyodin A,a pterocarpan derivative with unusual spirotetrahydrofuran ring from the roots of Indigofera stachyodes

Stachyodin A (1), a rearrangement product of pterocarpan featuring a 6/5/5/6 tetracyclic ring system with an unusual spirotetrahydrofuran ring, and stachyodin B (2), a new dihydrochalcone, along with five known analogues (3–7) were isolated from the roots of Indigofera stachyodes. The structures of 1 and 2 were elucidated on the basis of their HRESIMS and NMR spectroscopic data, and their absolute configurations were determined by X-ray crystallographic analysis and electronic circular dichroism (ECD) data, respectively. Compounds 2–4 showed inhibition of nitric oxide production in lipopolysaccharide-activated BV-2 microglial cells.     

Two pairs of new alkaloid enantiomers with a spiro [benzofuranone-benzazepine] skeleton from the bark of Juglans mandshurica

(±)-Juglanaloid A (1) and B (2), two pairs of novel naturally occurring alkaloid enantiomers bearing an unprecedented spiro [benzofuranone-benzazepine] skeleton, were isolated from the bark of Juglans mandshurica Maxim. The unusual 6, 5, 7, 6-cyclic system with a rare spiro cyclic center at C-4 was determined on the basis of spectroscopic data. Chiral separation of 1 and 2 yielded two pairs of enantiomers, 1a/1b and 2a/2b. The absolute configurations were established by comparing the experimental and calculated electronic circular dichroism spectra. The potential anti-AD properties of 1a/1b and 2a/2b were evaluated by the Thioflavin T assay.     

Structure of seven new vibsane-type diterpenoids from Viburnum awabuki

Seven new vibsane-type diterpenoids, 6-O-methyl-6,7-dihydroxyvibsanin B (1), 4-hydroxyvibsanin A (2), 14(R*),15-epoxyneovibsanin B (3), 14(S*),15-epoxyneovibsanin B (4), (8Z)-neovibsanin B (5), 18-O-methylvibsanin C (6), and (8Z)-vibsanin E (7), have been isolated from the leaves of Viburnum awabuki. Their structures have been elucidated by molecular mechanics 2 (MM2) calculations and comparison of the spectroscopic data, including ¹³C NMR data, with those of previously known compounds. Moreover, neovibsane-type diterpenoids 3, 4, and 5 enhanced the neurite outgrowth of NGF-mediated PC12 cells at a concentration of 40 μM.     

Reactivity of 1-boraadamantanes towards bis(trialkylstannyl)ethynes. First examples of 3-boratricyclo[5.3.1.1]dodecanes, and the molecular structure of a tetraalkyldiboroxane

1-Boraadamantane (1) and 2-ethyl-1-boraadamantane (1(2-Et)) react with bis(trialkylstannyl)ethynes (3), R₃Sn-CC-SnR₃ with R=Me (a), Et (b), in a 1:1 molar ratio by 1,1-organoboration under very mild conditions to give the 4-methylene-3-borahomoadamantane derivatives 4a,b and 7a,b, respectively, which are dynamic at room temperature with respect to deorganoboration. The compounds 4a,b react further with 3a,b by 1,1-organoboration to the tricyclic butadiene derivatives 5a,b. Attempts to crystallise 4a afforded the product of hydrolysis, the diboroxane 6a which was characterised by X-ray structural analysis. All products were characterised in solution by ¹H-, ¹¹B-, ¹³C- and ¹¹⁹Sn-NMR spectroscopy.     

Dye-sensitized photo-oxygenation of tryptophan

Dye-sensitized photo-oxygenation of L-tryptophan (1) has been studied at various pH and in various buffers. Disappearance of 1 in both acetate and phosphate buffers was rapid at higher pH. The tricyclic hydroperoxide (8) was the sole product in the oxidation of 1 over the range pH 3.6–7.1 in acetate and phosphate buffers. However, the oxidation of 1 in alkaline phosphate and borate buffers (pH 7.7–8.4) gave 5-hydroxyformylkynurenine (10) as the major product. The intermediate, 3a,5-dihydroxypyrroloindole (16), which may be formed from the tricyclic hydroperoxide (8) via the quinoneimine (15), was obtained in good yield by the immediate reduction of the reaction mixture with NaBH₄. Molecular oxygen (ground state) oxidation of 16 in the alkaline media provided 10. The similar oxidation and reduction of tryptamine (17a) gave 3a,5-dihydroxypyrroloindole (18b) which was not further oxidized to 5-hydroxyformylkynureamine. On the other hand, dye-sensitized photo-oxygenation of 1 in Na₂CO₃-AcOH (pH 7) gave formylkynurenine (3) as the major product.     

(+)/(−)-Yanhusuosines A and B,two dimeric benzylisoquinoline-protoberberine alkaloid atropo-enantiomers featuring polycyclic skeletons from Corydalis yanhusuo

(+)/(−)-Yanhusuosines A (1) and B (2), two pairs of trace benzylisoquinoline-protoberberine atropo-enantiomeric homodimers featuring an unprecedented 6/7/6/6/6/6 hexacyclic skeleton, were isolated from the tubers of Corydalis yanhusuo. The structures of (+)/(−)-1 and (+)/(−)-2 were elucidated using spectroscopic and quantum-chemical calculation approaches. (+)/(−)-Yanhusuosines A (1) and B (2) represent a new class of alkaloid dimers biogenetically constructed by a molecule of benzylisoquinoline with a unit of protoberberine via an intermolecular [4 + 3] cycloaddition. Their plausible biosynthetic pathways are discussed, and compound 2 exerted moderate inhibitory activity of NO formation in LPS induced RAW264.7 macrophages.     

Flavidanolides A and B from Isodon flavidus

A phytochemical investigation on Isodon flavidus led to the isolation of flavidanolide A(1), a rearranged diterpenoid featuring a six/seven/five-membered tricyclic skeleton, together with flavidanolide B(2), an uncommon heterodimeric diterpenoid consisting of a norabietane and a seco-isopimarane monomeric units. Their structures were elucidated by extensive spectroscopic data and single-crystal X-ray diffraction analyses. Their plausible biosynthetic routes were also proposed. In the bioassay, f...     

Novel resolution of the anthracyclinone intermediate by the use of (2r, 3r)-(+)- and (2s, 3s)-(-).1,4-bis(4-chlorobenzyloxy)butane-2,3-diol: a simple and efficient synthesis of optically pure 4-demethoxydaunomycinone and 4-demethoxyadriamycinone

(±)-7-Deoxy-4-demethoxydaunomycinone((±)-3) was found to be cleanly resolved by forming a mixture of the diastereomereic acetals((-)-9and(+)-10 or(+)-9 and(-)-10)with the title vicinal-diol(+)-or ( )-5), affording optically pure (R)-( )-3. The resolving agents (( + )- and ( )-5) were readily synthesized from unnatural(2S,3S)-(-)-tartaric acid((-)-6)or D-(-)-mannitol and natural (2R,3R)-(+)-tartaric acid((+)6), respectively. The undesired enantiomer ((S)-(+ )-3) obtained by the optical resolution could be racemized by heating with trifluoromethanesulfonic acid in aq acetic acid. Optically pure (R)-3 was elaborated to optically pure (+)-4-demethoxydaunomycinone ((+)-2b) and (+)-demethoxyadriamycinone ((+)-2a) by featuring highly stereoselective ( ? 20:1) introduction of the OH group into the C₇-position as a key step.     

Three new diterpenes from Jatropha curcas

Jatrophalactone (1) and jatrophalone (2), together with jatrophadiketone (3), a 6/6/6 tricyclic diterpene transformed from rhamnofolane skeleton, have been isolated from the methanolic extract of Jatropha curcas. The structures were established on the basis of extensive spectroscopic methods and further confirmed by X-ray crystallographic analysis. The cytotoxicity against selected cell lines was evaluated. Among them, compound 1 displayed cytotoxicity against HL-60, SMMC-7721, A-549, MCF-7, and SW480 cell lines with IC₅₀ values of 8.5, 20.6, 19.7, 20.1, and 19.2 μM, respectively. The possible biosynthetic pathways for 1 and 3 are proposed.     

Azabicyclo chemistry—V : Synthesis and stereochemistry of 7-substituted cis-octahydroindoles prepared via a nitrenium intermediate

As a potential route to 9-functionalized-2-azabicyclo[3.3.1]nonanes we have investigated the silver nitrate catalyzed solvolysis of N-chloro-N-methyl-2-cyclohexene-1-ethanamine (4a) in methanol. By this route we obtained 1-methyl-7(a)-methoxy-cis-octahydroindole (5a), 1-methyl-7-chloro-cis-octahydroindole (6a), 2-methy (8a) in the approximate ratio of 75:1:3:23, respectively. The structure proofs of 5a and 8a were accomplished by chemical interrelating the two and by double resonance NMR spectroscopy, while the structures of 6a and 7a were assigned by mass spectroscopy. Appropriate deuterium studies substantiated the mass spectral fragmentation pathways. Mechanistically we favor the formation of the products by invoking the intermediacy of a nitrenium ion.     

Synthesis of polyfunctionalized furans from 3-acetyl-1-aryl-2-pentene-1,4-diones

The BF₃-catalyzed cyclization of 3-acetyl-1-aryl-2-pentene-1,4-diones 1a-e in the presence of water in boiling tetrahydrofuran gave bis(3-acetyl-5-aryl-2-furyl)methanes 2a-e in 26-79% yields along with a small amount of 3-acetyl-5-aryl-2-methylfurans 3a-e. The exact structure of 2a was determined by X-ray crystallography. The use of a half volume of the solvent for the reaction of 1a resulted in the formation of 2,4-bis(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-phenylfuran (4) together with 2a and 3a. A similar reaction of 1a was carried out in the presence of 3-acetyl-5-(4-methylphenyl)-2-methylfuran (3d) to afford 4-(3-acetyl-5-phenyl-2-furfuryl)-3-acetyl-5-(4-methylphenyl)-2-methylfuran (5) in 49% yield. The BF₃-catalyzed reaction of 1a with 2,4-pentanedione in dry tetrahydrofuran at 23°C gave 3-(3-acetyl-5-phenyl-2-furfuryl)-4-hydroxy-3-penten-2-one (6a) and 3-(3-acetyl-2-methyl-4-phenyl-5-furyl)-4-hydroxy-3-penten-2-one (7a) in 66 and 24% yields, respectively. The product distribution depended on the reaction temperature. A similar reaction of 1b-e also yielded the corresponding trisubstituted furans 6b-e and tetrasubstituted furans 7b-e in good yields. These results suggested the presence of the furfuryl carbocation intermediate A during the reaction. The one-pot synthesis of 6a and 7a was also achieved by a similar reaction using phenylglyoxal. The deoxygenation of 1a with triphenylphosphine gave 3a in 88% yield, while 1a was treated with concentrated hydrochloric acid to yield 3-acetyl-2-chloromethyl-5-phenylfuran (8) which was quantitatively transformed in ethanol into 3-acetyl-2-ethoxymethyl-5-phenylfuran (9) and in water into 3-acetyl-5-phenylfurfuryl alcohol (10), respectively. In addition, the Diels-Alder reaction of cyclopantadiene with 1a gave the corresponding [4+2] cycloaddition products 11 and 12.     

Acetals and ethers-xiii Reaction products of 2-butenal with ethylene glycol

The unsaturated cyclic acetal, 2-(1-propenyl)-1,3-dioxolane (2), has been found as an intermediate product in the p-toluenesulfonic acid catalysed reaction of 2-butenal with an excess of ethylene glycol. The final product consisted of 2-[2-(2-hydroxyethoxy)-propyl]-1,3-dioxolane (3), and a small amount of geometric isomers of cis- and trans-5-(2-hydroxyethoxy)-7-methyl-1,4-dioxepane (4a and 4b, respectively).     

Another mode of heterocyclization of an enantiopure C2-symmetric bis-epoxide leading to the symmetric dialkyl sulfide

Reexamination of heterocyclization of an enantiopure C₂-symmetric bis-epoxide (7) with sodium sulfide is described. In addition to the reported processes leading to thiane (4a) and thiepane (6), another mode of cyclization was found to occur to a considerable extent, affording a symmetric dialkyl sulfide (5), and the structure of the main product reported (4a) has been revised. Conditions for the chemoselective formation of 6 were established, and effective transformation of 6 into 4 was accomplished by the modification of the processes.