Synthesis to determine the absolute configuration of (−)-pyricuol, a phytotoxin isolated from rice blast disease fungus Magnaporthe grisea

The absolute configuration of (−)-pyricuol, a phytotoxin isolated from rice blast disease fungus Magnaporthe grisea, was determined to be R by synthetic studies.     

Synthesis and plant growth inhibitory activity of both enantiomers of pyricuol, a phytotoxin isolated from rice blast disease fungus Magnaporthe grisea

Both enantiomers and racemate of pyricuol, a phytotoxin isolated from the rice blast disease fungus, Magnaporthe grisea, have been synthesized by using Stille coupling and [2,3]-Wittig rearrangement reactions as the key steps. Both enantiomers induced dark necrotic lesions on rice leaves almost equally, but did not affect the growth of rice second leaf sheath and the germination of lettuce. Only natural enantiomer promoted the root growth of rice and lettuce.     

Early diagnosis of blast fungus, Magnaporthe oryzae, in rice plant by using an ultra-sensitive electrically magnetic-controllable electrochemical biosensor

As one of the most destructive and widespread disease of rice, Magnaporthe oryzae (also called Magnaporthe grisea) has a significant negative impact on rice production. Therefore, it is still in high demand to develop extremely sensitive and accurate methods for the early diagnosis of Magnaporthe oryzae (M. oryzae). In this study, we developed a novel magnetic-controllable electrochemical biosensor for the ultra sensitive and specific detection of M. oryzae in rice plant by using M. oryzae’s chitinases (Mgchi) as biochemical marker and a rice (Oryza sativa) cDNA encoding mannose-binding jacalin-related lectin (Osmbl) as recognition probe. The proposed biosensor combined with the merits of chronoamperometry, electrically magnetic-controllable gold electrode and magnetic beads (MBs)-based palladium nano-particles (PdNPs) catalysis amplification, has an ultra-high sensitivity and specificity for the detection of trace M. oryzae in rice plant. It could be used to detect M. oryzae in rice plant in the initial infection stage (before any symptomatic lesions were observed) to help farmers timely manage the disease. In comparison with previous methods, the proposed method has notable advantages such as higher sensitivity, excellent specificity, short analysis time, robust resistibility to complex matrix and low cost etc. The success in this study provides a reliable approach for the early diagnosis and fast screening of M. oryzae in rice plant.     

The total synthesis of (−)-connatusin A, a hirsutane-type sesquiterpene isolated from the fungus Lentinus connatus BCC8996

The title sesquiterpenoid natural product 1 has been prepared for the first time using the enantiomerically pure cis-1,2-dihydrocatechol 3 as starting material. Key steps associated with the synthesis include a Diels-Alder cycloaddition reaction of the acetonide 5 with cyclopentenone (4) and an oxa-di-π-methane rearrangement of bicylco[2.2.2]octenone 6 derived from the initial adduct. The product of this sequence, the cyclopropannulated triquinane 7, was elaborated, over a further eight steps including those involving Upjohn dihydroxylation and Swern oxidation protocols, to the target 1. A single-crystal X-ray analysis served to confirm the structure of this synthetically derived material.     

First total synthesis and absolute configuration of naturally occurring (−)-hyacinthacine A7 and its (−)-1-epi-isomer

A convergent synthesis of the naturally occurring alkaloid (−)-hyacinthacine A₇, a glycosidase inhibitor of the pyrrolizidine class, is described. The homochiral starting material was tri-orthogonally protected DMDP 10, derived from d-fructose. Key steps of the synthesis were the carbon-chain lengthening at C(5′) in 10 to the α,β-unsaturated pyrrolidine ketone 12 and the one-pot construction of the bicyclic pyrrolizidine system of 13 and 14. Another key step was the partial inversion of the configuration at C(1) in 13 which led, after total deprotection, not only to the naturally occurring target molecule 9 but also to its (−)-1-epi-isomer 19.     

Synthesis and absolute configuration of brevione B, an allelochemical isolated from Penicillium sp.

Breviones A-E (1-5), allelochemicals isolated from Penicillium brevicompactum Dierckx, are structurally unique diterpenoid derivatives. The first synthesis of both enantiomers of brevione B (2) was accomplished by employing the double S_N2′-type tandem reaction as a key step, and the absolute configuration of the naturally occurring 2 was established.     

An enantioselective total synthesis of (S)-(−)-licochalcone E: determination of the absolute configuration

The absolute configuration of (−)-licochalcone E (1) was determined to be (S) via the first enantioselective total synthesis of the compound. The chirality in (S)-(−)-licochalcone E (1) was installed by asymmetric methylation of the Evans' oxazolidinone derivatives.     

First total synthesis of verbalactone, a macrocyclic dilactone isolated from Verbascum undulatum

Verbalactone, a new macrocyclic dilactone was synthesized efficiently in a steroselective manner involving a Barbier-Grignard reaction, a Sharpless asymmetric dihydroxylation, monotosylation, epoxidation, ring opening of the epoxide, hydrolysis and lactonization. A δ-lactone, (+)-(3R,5R)-3-hydroxy-5-decanolide was also formed along with the dimeric lactone.     

Synthesis and absolute configuration of cordiaquinone K, antifungal and larvicidal meroterpenoid isolated from the Panamanian plant, Cordia curassavica

Total synthesis of cordiaquinone K, a new antifungal and larvicidal meroterpenoid, is reported. The absolute configuration of cordiaquinone K was confirmed by the synthesis.     

Total synthesis and confirmation of the absolute stereochemistry of semiviriditoxin, a naphthopyranone metabolite from the fungus Paecilomyces variotii

The first total synthesis of (S)-semiviriditoxin 2 is described. The approach utilizes a tandem Michael-Dieckmann reaction between ortho-toluate 5 and dihydropyran-2-one 6 to construct the naphthopyranone core, the dihydropyran-2-one 6 being prepared from (R)-1,2-epoxy-4-butanol. Spectroscopic comparison of synthetic (S)-semiviriditoxin 2 with (R)-semivioxanthin 3, prepared in four steps from (R)-propylene oxide, confirmed the (S)-stereochemistry of natural semiviriditoxin from Paecilomyces variotii.     

First total synthesis of (−)-(3S,6R)-3,6-dihydroxy-10-methylundecanoic acid

The first total synthesis of (3S,6R)-3,6-dihydroxy-10-methylundecanoic acid was accomplished from commercially available 1-bromo-3-methylbutane in 11 steps and 25.8% overall yield. The key steps were asymmetric allylic alkylations via allyldiisopinocampheylborane and hydroboration-oxidation.     

First synthesis of (±)-sorgomol, the germination stimulant for root parasitic weeds isolated from Sorghum bicolor

Sorgomol, isolated from Sorghum bicolor, is the germination stimulant for seeds of root parasitic weeds. The first synthesis of (±)-sorgomol has been achieved by starting from ethyl 2-oxocyclohexanecarboxylate.     

First enantioselective synthesis of exiguamide,a nitrogen-containing spirocyclic sesquiterpene isolated from the marine sponge Geodia exigua

(+)-Exiguamide is a nitrogen-containing spirocyclic sesquiterpene isolated from the marine sponge Geodia exigua. This study aims to report the first synthesis of both enantiomers of exiguamide, featuring the stereoselective intramolecular cyclopropanation and stereoselective homoconjugate addition of azide to cyclopropyl ketone as the key steps.     

Stereoselective synthesis of (−)-allosedamine and (1R,3R)-HPA-12 from β-p-toluenesulfonamido-γ,δ-unsaturated sulfoxide

A stereoselective synthesis of (−)-allosedamine and HPA-12 is disclosed. The key steps of the synthesis include the diastereoselective synthesis of a β-sulfonamido unsaturated sulfoxide, elaboration of a bromohydrin via intramolecular sulfinyl group participation and a ring-closing metathesis reaction for the construction of the piperidine ring of allosedamine.     

Total synthesis of HM-1 and HM-2, aromatic sesquiterpenes isolated from the phytopathogenic fungus Helicobasidium mompa. Structure revision of HM-2

The structure assigned to the sesquiterpene HM-2 was found to be incorrect by total synthesis. A ring-closing metathesis based strategy was developed for the total synthesis of the aromatic sesquiterpene HM-1, which on functional group transformation established the structure of HM-2 as 23, a cuparene derivative.     

Structure revision of HM-3, an aromatic sesquiterpene isolated from the phytopathogenic fungus Helicobasidium mompa. First total syntheses of HM-3 and HM-4

The first total syntheses of HM-3 and HM-4, aromatic sesquiterpenes isolated from the phytopathogenic fungus Helicobasidium mompa, have been accomplished. The structure assigned to the sesquiterpene HM-3 was found to be incorrect by total synthesis. A Claisen rearrangement-RCM reaction based strategy was employed for the total synthesis of the aromatic sesquiterpene HM-4 (cuparene-1,2-diol), which on selective monoacetylation established the structure of HM-3, a cuparene derivative.     

A concise synthesis of (±)-pseudodeflectusin, an antitumor isochroman derivative isolated from Aspergillus sp.

A novel and concise synthesis of (±)-pseudodeflectusin (1), an antitumor isochroman derivative isolated from the culture broth of Aspergillus pseudodeflectus, was accomplished by starting from 4-(tert-butyldimethylsilyloxy)-1-pentyne (3) and diethyl 3-oxopentanedicarboxylate (5).     

The first synthesis of (±)-brevione B, an allelopathic agent isolated from Penicillium sp.

Breviones A∼E (1∼5), allelopathic agents isolated from Penicillium brevicompactum Dierckx, are structurally unique pentacyclic or hexacyclic diterpenoid derivatives. The first synthesis of brevione B (2) was achieved by employing the double S_N2′-type tandem reaction as a key step.     

Determination of the absolute configuration of the male aggregation pheromone, 2-methyl-6-(4′-methylenebicyclo[3.1.0]hexyl)hept-2-en-1-ol, of the stink bug Erysarcoris lewisi (Distant) as 2Z,6R,1′S,5′S by its synthesis

Lipase-catalyzed asymmetric acetylation of a mixture of (6R,1′S,4′S,5′R)- and (6R,1′R,4′R,5′S)-7′-norsesquisabinen-4′-ol (3) afforded a separable mixture of the recovered former and the acetate of the latter. The recovered alcohol was oxidized to (6R,1′S,5′R)-sesquisabina ketone (2), whose absolute configuration could be assigned by its CD comparison with (1R,5S)-sabina ketone (4). Conversion of (6R,1′S,5′R)-sesquisabina ketone (2) to the bioactive pheromone revealed the stereostructure of the male aggregation pheromone of the stink bug Erysarcoris lewisi (Distant) to be (2Z,6R,1′S,5′S)-2-methyl-6-(4′-methylenebicyclo[3.1.0]hexyl)hept-2-en-1-ol (sesquisabinen-1-ol, 1).     

The first enantiospecific synthesis of (−)-koumidine via the intramolecular palladium-catalyzed enolate driven cross coupling reaction. The stereospecific introduction of the 19-(Z) ethylidene side chain

The stereospecific synthesis of (−)-koumidine was realized by replacement of triphenylphosphine with tricyclohexylphosphine in the enolate driven palladium-catalyzed cross coupling process.