Infraspecific variation of sulfur-containing bisamides from Aglaia leptantha

KOtBu/DMF-Mediated Hydroalkylation of Alkenes via Benzylic C-H Bond Activation

Catalytic hydroalkylation reaction of alkenes with benzylic hydrocarbons involving t-BuOK/DMF-mediated benzylic C-H bond activation is demonstrated. This direct and operational simple protocol affords a rapid and reliable access to a wide scope of benzylic compounds in good-to-excellent yields. The benzylic C-H's of either activated diarylmethanes (pKa ∼ 32.2) and benzyl thioethers (pKa ∼ 30.8) or inert alkylbenzenes could all act as useful synthetic platforms to be conveniently alkylated under mild reaction conditions.

Comparative phytochemistry of flavaglines (= rocaglamides), a group of highly bioactive flavolignans from Aglaia species (Meliaceae)

Flavaglines are formed by cycloaddition of a flavonoid nucleus with a cinnamic acid moiety representing a typical chemical character of the genus Aglaia of the family Meliaceae. Based on biosynthetic considerations 148 derivatives are grouped together into three skeletal types representing 77 cyclopenta[b]benzofurans, 61 cyclopenta[bc]benzopyrans, and 10 benzo[b]oxepines. Apart from different hydroxy, methoxy, and methylenedioxy groups of the aromatic rings, important structural variation is created by different substitutions and stereochemistries of the central cyclopentane ring. Putrescine-derived bisamides constitute important building blocks occurring as cyclic 2-aminopyrrolidines or in an open-chained form, and are involved in the formation of pyrimidinone flavaglines. Regarding the central role of cinnamic acid in the formation of the basic skeleton, rocagloic acid represents a biosynthetic precursor from which aglafoline- and rocaglamide-type cyclopentabenzofurans can be derived, while those of the rocaglaol-type are the result of decarboxylation. Broad-based comparison revealed characteristic substitution trends which contribute as chemical markers to natural delimitation and grouping of taxonomically problematic Aglaia species. A wide variety of biological activities ranges from insecticidal, antifungal, antiprotozoal, and anti-inflammatory properties, especially to pronounced anticancer and antiviral activities. The high insecticidal activity of flavaglines is comparable with that of the well-known natural insecticide azadirachtin. Comparative feeding experiments informed about structure-activity relationships and exhibited different substitutions of the cyclopentane ring essential for insecticidal activity. Parallel studies on the antiproliferative activity of flavaglines in various tumor cell lines revealed similar structural prerequisites that let expect corresponding molecular mechanisms. An important structural modification with very high cytotoxic potency was found in the benzofuran silvestrol characterized by an unusual dioxanyloxy subunit. It possessed comparable cytotoxicity to that of the natural anticancer compounds paclitaxel (Taxol®) and camptothecin without effecting normal cells. The primary effect was the inhibition of protein synthesis by binding to the translation initiation factor eIF4A, an ATP-dependent DEAD-box RNA helicase. Flavaglines were also shown to bind to prohibitins (PHB) responsible for regulation of important signaling pathways, and to inhibit the transcriptional factor HSF1 deeply involved in metabolic programming, survival, and proliferation of cancer cells. Flavaglines were shown to be not only promising anticancer agents but gained now also high expectations as agents against emerging RNA viruses like SARS-CoV-2. Targeting the helicase eIF4A with flavaglines was recently described as pan-viral strategy for minimizing the impact of future RNA virus pandemics.

Direct alkylation of N,N-dialkyl benzamides with methyl sulfides under transition metal-free conditions

Amides are a fundamental and widespread functional group, and are usually considered as poor electrophiles owing to resonance stabilization of the amide bond. Various approaches have been developed to address challenges in amide transformations. Nonetheless, most methods use activated amides, organometallic reagents or transition metal catalysts. Here, we report the direct alkylation of N,N-dialkyl benzamides with methyl sulfides promoted by the readily available base LDA (lithium diisopropylamide). This approach successfully achieves an efficient and selective synthesis of α-sulfenylated ketones without using transition-metal catalysts or organometallic reagents. Preliminary mechanism studies reveal that the deprotonative aroylation of methyl sulfides is promoted by the directed ortho-lithiation of the tertiary benzamide with LDA.

Essential Oil and Major Non-Volatile Secondary Metabolites from the Leaves of Amazonian Piper subscutatum

The essential oil and the major non-volatile secondary metabolites from the leaves of Piper subscutatum (Miq.) C. DC. (Family Piperaceae), collected in the Ecuadorian Amazon, were analyzed for the first time in the present study. The essential oil was submitted to chemical and enantioselective analyses by GC-MS and GC-FID. (E)-β-caryophyllene (25.3-25.2%), β-chamigrene (10.3-7.8%), (E)-nerolidol (8.1-7.7%), β-selinene (7.2-7.7%), δ-cadinene (2.7-3.9%), bicyclogermacrene (3.7-2.4%), and β-pinene (2.6-3.4%) were the major components. The enantioselective analysis, carried out on a β-cyclodextrin-based column, showed four scalemic mixtures in which (1R,5R)-(+)-α-pinene, (1S,5S)-(-)-β-pinene, (S)-(-)-limonene, and (1R,2S,6S,7S,8S)-(-)-α-copaene were the major enantiomers, with enantiomeric excesses of 28.8%, 77.8%, 18.4%, and 6.0%, respectively. The study was complemented with the chemical analysis of the organic fraction dissolved in the hydrolate, whose major components were 6-methyl-5-hepten-2-one (63.7-64.4%) and linalool (6.5-6.0%). Concerning the non-volatile fraction, five lignans were the major components. (-)-Beilshminol B, (-)-grandisin, (-)-3',4'-methylenedioxy-3,4,5-trimethoxy-7,7'-epoxylignan, (-)-3',4'-methylenedioxy-3,4,5,5'-tetramethoxy-7,7'-epoxylignan, and (-)-3,4,3',4'-dimethylenedioxy-5,5'-dimethoxy-7,7'-epoxylignan were identified by means of NMR spectroscopy, mass spectrometry and X-ray crystallography. The absolute configuration 7S,8S,7'S,8'S was tentatively assigned to all of them.

Synthesis of α-arylthioacetones using TEMPO as the C3 synthon via a reaction cascade of sequential oxidation, skeletal rearrangement and C-S bond formation

Here, we present an unprecedented pathway to α-sulfenylated carbonyl compounds from commercially available thiols and universally employed TEMPO and its analogues, which act as C3 synthons through skeletal rearrangement under simple and metal-free conditions. Mechanism studies suggest that this reaction involves a consecutive radical oxidation and cation coupling process. TEMPO analogues and thiols serve as oxidants and reductive reagents, respectively, along the radical process, while in the coupling process, the former ones afford C3 synthons to couple with related sulfur sources.

α-C-H Alkylation of Methyl Sulfides with Alkenes by a Scandium Catalyst

The C-H addition of sulfides to alkenes is an atom-efficient route for the functionalization and modification of sulfide compounds through C-C bond formation, but this transformation is highly challenging. We report here the regioselective α-C(sp³)-H addition of a wide range of methyl sulfides to a variety of olefins and dienes by a half-sandwich scandium catalyst. This protocol provides a unique route for the synthesis of diverse sulfide derivatives through C-C bond formation at a sulfur-adjacent carbon atom in a 100% atom efficient fashion.

Configuration and stability of naturally occurring all-cis-tetrahydrofuran lignans from Piper solmsianum

First occurrence of all-cishexamethoxy-tetrahydrofuran lignans1aand1b, which are 6.5 kcal mol⁻¹less stable than the all-transisomer grandisin (2a).

Thioether-directed acetoxylation of C(sp2)–H bonds of arenes by palladium catalysis

The palladium-catalyzed acetoxylation of aromatic C(sp²)–H bonds utilizing thioether as the directing group was developed.

Potential antiviral lignans from the roots of Saururus chinensis with activity against Epstein-Barr virus lytic replication

Epstein-Barr virus (EBV) is a member of the γ-herpes virus subfamily and has been implicated in the pathogenesis of several human malignancies. Bioassay-guided fractionation was conducted on an EtOAc-soluble extract of the roots of Saururus chinensis and monitored using an EBV lytic replication assay. This led to the isolation of 19 new (1-19) and nine known (20-28) lignans. The absolute configurations of the new lignans were established by Mosher's ester, ECD, and computational methods. Eight lignans, including three sesquineolignans (19, 23, and 24) and five dineolignans (3, 4, 26, 27, and 28), exhibited inhibitory effects toward EBV lytic replication with EC50 values from 1.09 to 7.55 μM and SI values from 3.3 to 116.4. In particular, manassantin B (27) exhibited the most promising inhibition, with an EC50 of 1.72 μM, low cytotoxicity, CC50 > 200 μM, and SI > 116.4. This is the first study demonstrating that lignans possess anti-EBV lytic replication activity.

Terpenoid constituents and antifungal activity of Aglaia forbesii seed against phytopathogens

Two new trisnortriterpenoids possessing a γ-lactone ring linked to the D-ring of a 3,4-secodammarane skeleton in a 20R configuration, named isoeichlerialactone (1) and methyl isoeichlerialactone (2), were isolated from the seed of Aglaia forbesii , along with the three dammarane triterpenes, isocabralealactone (3), isoeichlerianic acid (4), and aglinin A (5), the sesquiterpene spathulenol (6), and the widespread sterols β-sitosterol and stigmasterol. Their structures were established based on detailed spectroscopic analysis. Antifungal activity of A. forbesii seed against three phytopathogens, Phytophthora botryosa , P. palmivora , and Rigidoporus microporus , was carried out using the mycelium inhibition test and broth microdilution technique. Superior activity was exhibited by hexane and dichloromethane fractions containing the compounds 1, 4, and 5 as the main components. Subsequent antiphytopathogenic fungi tests proved that compounds 1, 4, and 5 possessed good antifungal activity.

6α-Acetoxy-gedunin

THE TITLE COMPOUND [SYSTEMATIC NAME: (1S,3aS,4aR,4bS,5S,6R,6aR,10aR,10bR,12aS)-5,6-bis-(acet-yloxy)-1-(3-fur-yl)-1,5,6,6a,7,10a,10b,11,12,12a-deca-hydro-4b,7,7,10a,12a-penta-methyl-oxireno[c]phenanthro[1,2-d]pyran-3,8(3aH,4bH)-dione], C(30)H(36)O(9), is a limonoid-type triterpene isolated from Aglaia elaeagnoidea (A. Juss.) Benth. (Meliaceae) from Queensland, northern Australia. It contains the gedunin core of four trans-fused six-membered rings with an oxirane ring annelated to the fourth ring. A terminal 3-furyl unity and two acet-oxy groups in a mutual cis-disposition supplement the mol-ecule. A comparison between the gedunin cores of the title compound, the parent compound gedunin, and three further gedunin derivatives revealed considerable variations in their conformation stemming from the conformational lability of the first screw-boat ring and the third twist-boat ring. A sensitive measure for the third ring is one C-C-C-C torsion angle, which is 14.2 (2)° in the title compound, but varies in other cases from ca 20 to ca -40°. In the crystalline state, 6α-acetoxy-gedunin shows ten comparatively weak C-H⋯O inter-actions, with H⋯O distances in the range of 2.33-2.69 Å.

Amide-esters from Aglaia tenuicaulis--first representatives of a class of compounds structurally related to bisamides and flavaglines

Six amide-esters and two sulphur-containing bisamides were isolated from the leaves, stem and root bark of Aglaia tenuicaulis together with two bisamides from the leaves of A. spectabilis. Their structures were elucidated by spectroscopic methods. The co-occurrence of amide-esters and bisamides suggests close biosynthetic connections replacing only one nitrogen atom of putrescine with oxygen. Putrescine appears to be the common building block linked to various acids from which the cinnamoyl moiety represents the prerequisite for an incorporation of bisamides into flavaglines. Corresponding amide-esters are apparently not incorporated, but closely related amide-alcohol derivatives were found as part of benzopyran and benzofuran flavaglines. The structure of a amide-alcohol is described, representing an artifact due to hydrolysis of an amide-ester during TLC purification. A hypothetical amide-amine building block is suggested to form the characteristic pyrimidinone structures only found in benzofuran flavaglines. Structural and biosynthetic connections between amide-esters, bisamides and flavaglines are discussed and the chemotaxonomic significance of accumulating specific derivatives within the genus Aglaia is highlighted.

Cytotoxic flavaglines and bisamides from Aglaia edulis

Two new cyclopenta[b]benzofurans, aglaroxin A 1-O-acetate (2) and 3'-methoxyaglaroxin A 1-O-acetate (3), a new benzo[b]oxepine, 19,20-dehydroedulisone A (4), and five new cyclopenta[bc]benzopyrans, edulirin A (5), edulirin A 10-O-acetate (6), 19,20-dehydroedulirin A (7), isoedulirin A (8), and edulirin B (9), were isolated from the bark of Aglaia edulis, along with one known cyclopenta[b]benzofuran, aglaroxin A (1). Additionally, four new amides, aglamides A-D (10-13), as well as three known compounds, aglalactone, scopoletin, and 5-hydroxy-3,6,7,4'-tetramethoxyflavone, were isolated from the leaves and/or twigs of this species. The structures of the new compounds (2-13) were elucidated by interpretation of their spectroscopic data. All isolates obtained in this study were evaluated for cytotoxicity against both several human cancer cell lines (Lu1, LNCaP, and MCF-7) and a nontumorigenic (HUVEC) cell line. Among these isolates, the cyclopenta[b]benzofurans (1-3) exhibited potent in vitro cytotoxic activity (ED50 range 0.001 to 0.8 microg/mL). Aglaroxin A 1-O-acetate (2) was further evaluated in the in vivo P388 lymphocytic leukemia model, by intraperitoneal injection, but found to be inactive in this model.

Antiplasmodial activity of sesquilignans and sesquineolignans from Bonamia spectabilis

Phytochemical re-investigation of the aerial parts of Bonamia spectabilis (Convolvulaceae) led to the isolation of four minor tetrahydrofuran-type sesquilignans (bonaspectins E-H) together with the known neolignan virolongin A and the known lignan rel-(7S,8R,7'R,8'R)-3,3',4,4',5,5'-hexamethoxylignan. Their structures were established on the basis of spectral data. These six compounds as well as further seven lignanoids from B. spectabilis, characterised previously, were tested for their antiplasmodial activity against a chloroquine-sensitive strain (PoW) and a chloroquine-resistant clone (Dd2) of Plasmodium falciparum. Bonaspectin C 4"-O-glucoside, its aglycone, and bonaspectin D 4"-O-glucoside revealed the highest antiplasmodial activities (IC50 values: 1.3, 2.0, 6.5 microM [PoW]; 1.7, 4.6, 3.7 microM [Dd2], respectively).

Aglacins A-D, first representatives of a new class of aryltetralin cyclic ether lignans from Aglaia cordata

Four new metabolites, aglacins A-D (1-4), were identified from the methanol extract of the stem bark of Aglaia cordata. These compounds represent a new class of aryltetralin cyclic ether lignan. The structure of aglacin A (1) including the absolute configuration was elucidated by interpretation of spectral data, X-ray crystal structure determination, and employing the modified Mosher's method. In addition, three other derivatives, aglacins B-D (2-4), were isolated and identified by spectral means.

Antimalarial compounds from Rhaphidophora decursiva

Bioassay-directed fractionation led to the isolation of 14 compounds, six of which possess antimalarial activity, from the dried leaves and stems of Rhaphidophora decursiva. Polysyphorin (1) and rhaphidecurperoxin (6) showed strong activities against Plasmodium falciparum. Rhaphidecursinol A (2), rhaphidecursinol B (3), grandisin (4), and epigrandisin (5) were less active against the same organism. Among the isolates, rhaphidecursinol A (2) and rhaphidecursinol B (3) were determined to be new neolignans, and rhaphidecurperoxin (6) is a new benzoperoxide. Known compounds isolated include polysyphorin (1), grandisin (4), epigrandisin (5), (+)-medioresinol, (-)-pinoresinol, (-)-syringaresinol, (+)-glaberide I, (+)-dehydrovomifoliol, (-)-liliolide, (-)-hydroxydihydrobovolide, and N-butylbenzamide, of which compound 1 appears worthy of further evaluation as an antimalarial agent. Structure elucidation and identification were accomplished by spectroscopic means including 1D and 2D NMR analyses.

Insecticidal flavaglines and other compounds from Fijian Aglaia species

Bioassays with lipophilic crude extracts of four Fijian Aglaia species against Spodoptera littoralis displayed strong insecticidal activity for A. basiphylla and A. gracilis, whereas A. archboldiana and A. vitiensis did not have any significant effects. The insect toxicity of A. basiphylla was caused by the well known benzofuran flavaglines rocaglamide, desmethylrocaglamide and aglafoline. In contrast, A. gracilis contained four related pyrimidinone derivatives in the root and stem bark, including two new congeners named marikarin and 3'-hydroxymarikarin. Moreover, two new putrescine bisamides, secoodorine and secopiriferine, a new benzopyran flavagline. desacetylaglain A. and a new norsesquiterpene were isolated from the leaves together with three known bisamides and 3-hydroxy-5,7,4'-trimethoxyflavone. The structures of the new compounds were elucidated by spectroscopic methods. Comparative feeding assays within the active pyrimidinone flavaglines showed that the free hydroxy group in aromatic ring A of marikarin diminishes insecticidal activity.