Alkyne‐Mediated Approach to the Synthesis of (4R,5R)‐5‐Hydroxy‐4‐decanolide and (−)‐Muricatacin

The asymmetric synthesis of two naturally occurring 5‐hydroxy‐γ‐butyrolactones, (4R,5R)‐5‐hydroxy‐4‐decanolide ( 1a ) and (?)‐muricatacin ( 2 ), is described using a general alkyne‐mediated strategy. The key steps involved are Sonogashira coupling for the desired carbon‐chain extension followed by Sharpless asymmetric dihydroxylation to construct the hydroxy‐lactone framework.     

An Expeditious Access to Enantiomerically Pure cis‐Dialkyl‐Substituted γ‐ and δ‐Lactones

A facile general route to enantiomerically pure 3,4‐cis‐dialkyl‐substituted γ‐lactones and 4,5‐cis‐dialkyl‐substituted δ‐lactones by TiCl₄‐mediated Evans asymmetric aldolization as the key step is exemplified by synthesis of cis‐(3R,4R)‐3‐methyldecan‐4‐olide and (4R,5R)‐aerangis lactone.     

Sesquiterpenoids and Phenylpropane Derivatives from Sonchus uliginosus

Six new compounds were isolated from the whole plant of Sonchus uliginosus, including three eudesmane‐type sesquiterpenoids (1β,6α)‐1,6,14‐trihydroxyeudesm‐3‐en‐12‐oic acid γ‐lactone ( 1 ), (1β,6α)‐1,6,14‐trihydroxyeudesma‐3,11(13)‐dien‐12‐oic acid γ‐lactone ( 2 ), and (1β,6α)‐1,6‐dihydroxy‐14‐O‐[(4‐hydroxyphenyl)acetyl]eudesma‐3,11(13)‐dien‐12‐oic acid γ‐lactone ( 3 ), and three phenylpropane derivatives, 4‐hydroxy‐γ,3,5‐trimethoxybenzenepropanol ( 6 ), γ,3,4,5‐tetramethoxybenzenepropanol ( 7 ), and γ,3,4,5‐tetramethoxybenzenepropanol acetate ( 8 ), together with the two known compounds 4 and 5 . The new structures were elucidated by means of spectroscopic methods, such as IR, EI‐MS, HR‐ESI‐MS, 1D‐ and 2D‐NMR, and by comparison of the spectroscopic data with those reported for structurally related compounds.     

Stereoselective Total Synthesis of Botryolide E and Ophiocerin C

A highly stereoselective approach to the total synthesis of the γ‐lactone derivative botryolide E and tetrahydropyran derivative ophiocerin C via a common polyketide precursor by means of Prins cyclization and MacMillan α‐aminoxylation sequence is described. The method can conveniently be utilized for the preparation of further related γ‐lactone and tetrahydropyran derivatives.     

Menverins A–D,New Highly Oxygenated Guaiane Lactones from Hainan Gorgonian Menella verrucosa (Brundin)

Four new highly oxygenated guaiane lactones, menverins A–D ( 1 – 4 ), were isolated from the gorgonian Menella verrucosa (Brundin ) from the South China Sea. Their structures and relative configurations were elucidated on the basis of spectroscopic data. All compounds contain a conjugated α‐methyl‐substituted α, β‐unsaturated γ‐lactone moiety, a C(8)?C(9) conjugated with the γ‐lactone moiety, and an exocyclic methylene group at C(4) (trivial numbering).     

Synthesis of New Furo[3,4‐b]quinolin‐1(3H)‐one Scaffolds Derived from γ‐Lactone‐Fused Quinolin‐4(1H)‐ones

In the context of our aim of discovering new antitumor drugs among synthetic γ‐lactone‐ and γ‐lactam‐fused 1‐methylquinolin‐4(1H)‐ones, we developed a rapid access to 5‐methyl‐1,3‐dioxolo[4,5‐g]furo[3,4‐b]quinoline‐8,9(5H,6H)‐dione ( 9 ) exploiting the γ‐lactone‐fused chloroquinoline 10 previously synthesized in our laboratory (Scheme 1). We also elaborated efficient synthetic methods allowing for a rapid access to two nonclassical bioisosteres of 9 , i.e., a deoxy and a carba analogue. The deoxy analogue 11 was prepared in two steps from the γ‐lactone‐fused quinoline 13 which was also the synthetic precursor of 10 (Scheme 1). The carba analogue 6,9‐dihydro‐5‐methyl‐9‐methylene‐1,3‐dioxolo[4,5‐g]furo[3,4‐b]quinolin‐8(5H)‐one ( 12 ) was easily prepared by HCl elimination from the 9‐(chloromethyl)dioxolofuroquinoline 15 , which was obtained via a three‐component one‐pot reaction from N‐methyl‐3,4‐(methylenedioxy)aniline (=N‐methyl‐1,3‐benzodioxol‐5‐amine; 16 ), commercially available chloroacetaldehyde, and tetronic acid ( 17 ) (Scheme 2).     

Tropone Is a Mere Ketone for Cycloadditions to Ketenes

Tropone ( 1 ) reacts with ketenes 2 to yield [8+2] cycloadducts, the γ‐lactones 3 . The concerted [8+2] cycloaddition path is formally symmetry‐allowed, but we established that it is unfavorable. Careful low‐temperature NMR (¹H, ¹³C, and ¹⁹F) spectroscopies of the reaction of diphenyl ketene ( 2b ) or bis(trifluoromethyl) ketene ( 2c ) with tropone ( 1 ) allowed the direct detection of a β‐lactone intermediates 5b , c and novel norcaradiene species 6b , c in head‐to‐head configurations. The [2+2] cycloadducts 5b , c equilibrated with the norcaradienes 6b , c . The β‐lactones 5b and 5c were converted to the γ‐lactones 3b and 3c , respectively, in quantitative yields. The DFT calculations showed that the concerted [8+2] cycloaddition is unfavorable. The first step of the calculated reaction 1 + 2c is a cycloaddition which leads to a dioxetane intermediate. This initial [2+2] cycloadduct is isomerized to the β‐lactone 5c via the first zwitterionic intermediate. The β‐lactone 5c is further isomerized to the product γ‐lactone 3c via the second zwitterion intermediate. Thus, 3c is not formed via the well‐established two‐step mechanism including zwitterionic intermediates but via a five‐step mechanism composed of a [2+2] cycloaddition and subsequent isomerization (Scheme 12).     

Ypsilactosides A and B,Two New C22‐Steroidal Lactone Glycosides from Ypsilandra thibetica

Two new C₂₂‐steroidal lactone glycosides, ypsilactosides A ( 1 ) and B ( 2 ), were isolated from the EtOH extract of the whole plant of Ypsilandra thibetica. Their structures were established as (3β,5α,16β,20S)‐3,16‐dihydroxy‐6‐oxopregnane‐20‐carboxylic acid γ‐lactone 3‐(β‐D ‐glucopyranoside) ( 1 ) and (3β,16β)‐3,16‐dihydroxypregna‐5,20‐diene‐20‐carboxylic acid γ‐lactone 3‐{O‐α‐L ‐rhamnopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→4)‐O‐[α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐glucopyranoside} ( 2 ) on the basis of extensive spectroscopic analyses and chemical degradations.     

Novel Concise Synthesis of (-)-Clausenamide

A six‐step synthesis of (?)‐clausenamide is described. Optically pure (R,E)‐1,3‐diphenylallylic alcohol was acetylated and then subjected to an Ireland‐Claisen rearrangement, giving the γ,δ‐unsaturated acid, which underwent a substrate‐induced stereoselective bromolactonization to afford the expected all‐equatorial substituted bromo‐δ‐lactone. An unusual chemo‐selective aminolysis of the lactone resulted in the formation of a γ,δ‐epoxy‐amide in stereospecific manner. Base‐promoted cyclization of this intermediate and the subsequent Davis oxidation furnished the synthesis, delivering the final product in >99% ee and up to 34% overall yield.     

Verticillane and Norverticillane Diterpenoids from the Formosan Soft Coral Cespitularia hypotentaculata

Five new diterpenes, cespihypotins W–Z ( 1 – 4 , resp.) and cespihypotone ( 5 ) have been isolated from the AcOEt‐soluble fraction of the Formosan soft coral Cespitularia hypotentaculata. Two of them having the norverticillane skeleton, i.e., 1 and 2 , and the other three, 3 – 5 , possessing a verticillane skeleton. The structures were established as (+)‐(1βH,7E)‐6β,11β‐dihydroxynorverticilla‐4(18),7‐diene‐10,12‐dione ( 1 ), (+)‐(1βH,7E)‐6β‐acetoxy‐11β‐hydroxynorverticilla‐4(18),7‐diene‐10,12‐dione ( 2 ), (?)‐(1βH,7E)‐6β‐acetoxyverticilla‐4(18),7,11‐triene‐10,12‐γ‐lactone ( 3 ), (+)‐(1βH,7E)‐6β‐acetoxy‐10‐hydroxyverticilla‐4(18),7,11‐triene‐10,12‐γ‐lactone ( 4 ), and (+)‐(1βH,3Z)‐10β‐hydroxy‐6‐oxoverticilla‐3,11‐diene‐10,12‐γ‐lactone ( 5 ), respectively, on the basis of 1D‐ and 2D‐NMR spectroscopic analyses.     

A Novel Atisane Diterpenoid from Spiraea japonica var. acuta

A novel ent‐atisane lactone, spiramilactone E ( 1 ), was isolated from Spiraea japonica var. acuta Yu . Its structure was elucidated by extensive spectroscopic analyses, and unequivocally confirmed by single‐crystal X‐ray diffraction (Fig. 2). Compound 1 contains a γ‐lactone moiety between the 6‐OH function and C(20), and β‐configuration for the 7‐OH group, in contrast to known related diterpenes previously isolated from the S. japonica complex.     

Synthetic Studies on Camptothecins. Part 1

A six‐step asymmetric total synthesis of (20S)‐camptothecin ( 1 ) has been accomplished in 25% overall yield starting from the known pyridone 3 . The key steps in this synthesis are the chemoselective Ni‐catalyzed hydrogenation of 3‐cyanopyridone 6 to 3‐formylpyridone 7 in AcOH/pyridine/H₂O and the Davis asymmetric hydroxylation of tricyclic lactone 4 utilizing a chiral N‐sulfonyloxaziridine into (4′S)‐tricyclic hydroxylactone 2 .     

Chemo‐Enzymatic Synthesis and Determination of the Absolute Configuration of Both Enantiomers of Methyl trans‐5‐Oxo‐2‐pentylpyrrolidine‐3‐carboxylate Precursors of the Aza Analogues of (+)‐ and (−)‐Methylenolactocin

Enantiomerically pure methyl esters of (+)‐(2R,3S)‐ and (−)‐(2S,3R)‐5‐oxo‐2‐pentylpyrrolidine‐3‐carboxylic acid with 99% and 98% ee were obtained by enzymatic resolution of the corresponding racemic mixture using α‐chymotrypsin and pig‐liver acetone powder, respectively. Their absolute configurations were established by chemical methods, i.e., conversion of the trans‐γ‐lactam moiety to the corresponding γ‐lactone of known configuration. The favorable interactions between the trans‐γ‐lactam and α‐chymotrypsin were rationalized by molecular‐mechanics calculations, which suggest a different situation for the cis‐diastereoisomer.     

A Short Synthesis of Clionamine D

Herein we describe a scalable four‐step preparation of α‐methylene‐γ‐lactone 3 from steroidal sapogenin. This method allowed a facile synthesis of clionamine D, a natural aminosteroid with potent autophagy bioactivity and unprecedented chemical structure.     

Adenanthusone,a New Ursane Type Nortriterpenoid from Isodon adenanthus

A new ursane‐type nortriterpenoid, adenanthusone (=(11α,12α)‐4‐demethyl‐11,12‐epoxy‐3,13‐dihydroxy‐2‐oxoursa‐3,20(30)‐diene‐28‐oic acid γ‐lactone; 1 ) was isolated from Isodon adenanthus. Its structure was determined by NMR spectra and X‐ray crystallographic diffraction analysis. The biogenetic implication of the nortriterpene is discussed.     

Asymmetric α‐Hydroxylation of a Lactone with Vinylogous Pyridone by Using a Guanidine–Urea Bifunctional Organocatalyst: Catalytic Enantioselective Synthesis of a Key Intermediate for (20S)‐Camptothecin Analogues

We have developed a catalytic asymmetric synthesis of (S)‐4‐ethyl‐6,6‐(ethylenedioxy)‐7,8‐dihydro‐4‐hydroxy‐1H‐pyrano[3,4‐f]indolizine‐3,10(4H)dione ( 5 a ), a synthetic intermediate for (20S)‐camptothecin analogues. A key step in this synthesis is an asymmetric α‐hydroxylation of a lactone with a vinylogous pyridone structure ( 8 a ) by using a guanidine–urea bifunctional organocatalyst. The present oxidation was successfully applied to the synthesis of C20‐modified derivatives of (+)‐C20‐desethylbenzylcamptothecin ( 13 ).     

Four New Eudesmane Sesquiterpenoid Lactones from Chloranthus serratus

Four new eudesmane sesquiterpenoids endowed with an α,β‐unsaturated γ‐lactone five‐membered ring, serralactones A–D ( 1 – 4 , resp.), along with seven known sesquiterpenoids, were isolated from the whole plant Chloranthus serratus. Their structures and relative configurations were established on the basis of extensive spectroscopic analyses.     

Highly Enantioselective Methanolysis of Meso‐Cyclic Anhydride Mediated by Bifunctional Thiourea Cinchona Alkaloid Derivatives: Access to Asymmetric Total Synthesis of (+)‐Biotin

An enantioselective asymmetric total synthesis of (+)?biotin ( 1 ) via the Hoffmann–Roche lactone–thiolactone strategy has been accomplished from commercially available cis‐1,3‐dibenzyl‐2‐imidazolidone‐4,5‐dicarboxylic acid ( 2 ). Strategic transformations include a cinchona alkaloid‐based bifunctional thiourea mediated methanolytic desymmetrization of prochiral cyclic anhydride 3 to produce the enantiomerically enriched precursor of Roche lactone 5 and an improved introduction of the 4‐carboxybutyl side chain at C‐4 position of Roche thiolactone 6 via Grignard reaction.     

New Phenolic Glycosides from Clematis mandshurica

Three new phenolic glycosides, clemomandshuricosides A–C ( 1 – 3 , resp.) and two new D ‐ribono‐γ‐lactone derivatives, 4 and 5 , were isolated from the roots and rhizomes of Clematis mandshurica Rupr ., together with six known compounds. Their structures were elucidated on the basis of chemical, physicochemical, and spectroscopic evidence.