Total synthesis and biological activity of neopeltolide and analogues

Combining the core structure of neopeltolide, lactone 16 a, with the oxazole-containing side chain 23 via a Mitsunobu reaction provided the cytotoxic natural product neopeltolide (2). The side chain 23 was prepared from oxazolone 24 via the corresponding triflate. Key steps in the preparation of 23 were a Sonogashira coupling, an enamine alkylation, and a Still-Gennari Horner-Emmons reaction. By changing the Leighton reagent in the allylation step, the 11-epimer of lactone 16 a, compound 50 was prepared. This led to 11-epi-neopeltolide 51. The 5-epimer of neopeltolide, compound 52, could be obtained from the minor isomer of the Prins cyclization. Furthermore, a range of analogues with modifications in the side chain were prepared. All derivatives were checked for toxicity effects on mammalian cell cultures and inhibitory effects on NADH oxidation in submitochondrial particles of bovine heart. Modifications in the lactone part are tolerated to some degree. On the other hand, shortening the distance between the oxazole and the lactone causes a significant drop in activity. Analogue 65 with an additional double bond is equally or even more active than neopeltolide itself.     

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.     

Synthesis of the fully functionalized core structure of the antibiotic abyssomicin C

[reaction: see text] The fully functionalized core structure 23 of abyssomicin C (6) containing an oxabicyclooctane ring and a tetronate was prepared via a Diels-Alder approach. After hydroxylation of lactone 10 to the alpha-hydroxylactone 12, lactone opening led to the hydroxy ester 16. A directed epoxidation furnished the desired syn-epoxide 20. Acetylation of the tertiary hydroxyl group, followed by intramolecular Claisen condensation, gave directly the core structure 23.     

An improved synthesis of (−)-brevisamide, a marine monocyclic ether amide of dinoflagellate origin

An improved synthesis of (−)-brevisamide a marine cyclic ether isolated from the red-tide dinoflagellate Karenia brevis was achieved. The ether ring portion was constructed from an unsaturated lactone, which was prepared enantioselectively via an Evans aldol reaction and one-pot lactonization in the presence of excessive base after an Ando reaction. The ether ring and a dienol side chain fragment were connected via Suzuki-Miyaura coupling.     

Enantioselective synthesis of (S)-homocitric acid lactone and (R)-per-homocitric acid lactone involving organocatalysis

A concise enantioselective synthesis of (S)-homocitric acid lactone and its homolog, via an organocatalytic vinylogous Mukaiyama–Michael reaction of a silyloxy furan derivative and acrolein, is described.     

Lactone synthesis based on atom transfer carbonylation

[reaction: see text] Five- to seven-membered lactones were prepared from omega-hydroxyalkyl iodides and CO by atom transfer carbonylation without the need for transition metal catalysts. The reaction proceeds via a hybrid radical/ionic mechanism in which the intramolecular alcoholysis of an omega-hydroxyacyl iodide, arising from atom transfer carbonylation, leads to the lactone.     

Approach toward the total synthesis of griseoviridin: formation of thioethynyl and thiovinyl ether-containing nine-membered lactones through a thioalkynylation-macrolactonization-hydrostannylation sequence

Synthesis of the lactone core 17 of 8-epi-griseoviridin is reported. Thioethynyl derivative 11 was easily prepared via an anionic coupling reaction between acetylenic compound 9 and sulfone 10. After desilylation of 11, saponification of the resulting hydroxy ester 12 followed by a Mitsunobu macrolactonization furnished the unusual triple-bond-containing nine-membered lactone 13 in 50% yield for the last two steps (39% after recrystallization). Stannylation under Magriotis conditions led to the pure regio- and stereocontrolled vinyltin 14 (80% yield). After a Sn/I exchange, palladium-catalyzed carbonylation delivered either the ester lactone 16 in 67% yield or the propargyl amide 17 in 65% yield. Synthesis of propargyl amide 17 of the lactone core of 8-epi-griseoviridin was achieved in 11.9% overall yield from commercial L-cystin dimethyl ester (nine steps).     

Asymmetric total synthesis of bacillariolide III, a marine oxylipin

[reaction: see text] The asymmetric total synthesis of bacillariolide III has been achieved via 15 linear steps in 14.6% overall yield. The key feature of this synthetic route involves the highly stereoselective construction of the vinyl-substituted bicyclic lactone by an intramolecular Pd(0)-catalyzed allylic alkylation and its facile conversion to the hydroxy bicyclic lactone skeleton of bacillariolide III, induced by stereoselective vinylcerium addition to the aldehyde. In addition, the (Z)-pentenoic acid was efficiently introduced by the internal hydroxy group tethered ring-closing metathesis (RCM).     

Accidental discovery of a ‘longer-range’ vinylogous Pummerer-type lactonization: formation of sulindac sulfide lactone from sulindac

Unexpected formation of sulindac sulfide lactone occurred when sulindac was treated with oxalyl chloride and triethylamine. Structurally analogous sulindac sulfide and indomethacin did not undergo such lactonization under similar reaction conditions. We believe that the sulfoxide function in sulindac plays a pivotal role possibly via a ‘longer-range’ vinylogous Pummerer-type reaction as a driving force for the observed lactonization. The structure of the lactone was confirmed by single crystal X-ray analysis.     

Total synthesis of crisamicin A

Stereoselective total synthesis of natural product crisamicin A (1) was accomplished for the first time via the Pd/TMTU-catalyzed alkoxycarbonylative annulation to generate a unique cis-pyran-fused lactone, an intermolecular Diels-Alder reaction to construct the pyranonaphthoquinone unit, and a novel Pd-thiourea pincer complex-catalyzed homocoupling of functionalized naphthoquinones.     

Stereospecific Sulfur-Mediated Cleavage of a Spirocyclobutanone: Synthesis of a Fully Functional Precursor to the CP Compounds

A reaction sequence made up of a Sakurai reaction, ketene cyclization, sulfur-directed Baeyer–Villiger reaction, and tandem lactone cleavage/isomerization provided the fully functionalized core of the CP compounds. Key steps were the methanolysis of 1 , which leads via 2 to the CP precursor 3 .     

Transition-metal-catalyzed group transfer reactions for selective C-H bond functionalization of artemisinin

Three types of novel artemisinin derivatives have been synthesized through transition-metal-catalyzed intramolecular carbenoid and nitrenoid C-H bond insertion reactions. With rhodium complexes as catalysts, lactone 11 was synthesized via carbene insertion reaction at the C16 position in 90% yield; oxazolidinone 13 was synthesized via nitrene insertion reaction at the C10 position in 87% yield based on 77% conversion; and sulfamidate 14 was synthesized via nitrene insertion reaction at the C8 position in 87% yield.     

Enantiocontrolled synthesis of jasmonates via tandem retro-Diels-Alder-ene reaction activated by a silyl substituent

[reaction: see text] An enantiocontrolled synthesis of (-)-methyl 6-epi-cucurbate and (+)-methyl jasmonate was established from a chiral tricyclic lactone via a new type of tandem retro-Diels-Alder-ene reaction activated by a trimethysilyl substituent as the key step.     

Asymmetric total synthesis of octalactin B using a new and rapid lactonization

A method for the synthesis of octalactin B is established via a new and quite effective mixed-anhydride lactonization for the synthesis of an eight-membered ring moiety using 2-methyl-6-nitrobenzoic anhydride with DMAP. Both an optically active linear precursor of the lactone and a side chain of octalactins are prepared by the enantioselective aldol reaction of ketene silyl acetals with aldehydes.     

Formal synthesis of (±)-camptothecin via tricyclic lactone as key synthon

Formal synthesis of (±)-camptothecin via CDE tricyclic lactone employing tandem Michael addition, Dieckmann condensation and addition-elimination reaction as key steps starting from glycinate is described.     

Total synthesis of absinthin

(+)-Absinthin, a structurally unique triterpene, has been efficiently constructed in nine reaction steps and in 18.6% overall yield from O-acetylisophotosantonic lactone. The synthesis features Mitsunobu arylselenylation, oxidative elimination of allylic arylselenides, biomimetic dimerization via regio- and stereospecific Diels-Alder reaction, and a four-step stereochemical inversion of a highly sterically congested tertiary alcohol. This approach has not only tackled the formidable synthetic challenges in assembling structurally complex (+)-absinthin but also paved an efficient synthetic route to a series of medicinally attractive absinthin analogues.     

内酯开环塔斯品碱香豆素酯衍生荧光化合物的合成及其抗癌活性

以异香草醛为原料,经溴代、苄基保护、氧化、Ulmman反应和还原等6步反应合成了塔斯品碱内酯开环衍生物（化合物8）。 通过在其结构中分别引入含有2种不同取代基的香豆素衍生物,设计、合成了2个新型荧光性的内酯开环塔斯品碱香豆素酯衍生物（化合物9a和9b）。 产物结构经IR、1H NMR和MS进行了表征。 同时,对产物的荧光特性及其对乳腺肿瘤细胞增殖的抑制活性进行了初步测定。     

A dirhodium(II)-carbenoid route to (-)- and (+)-Geissman-Waiss lactone: synthesis of (1R,7R,8R)-(-)-turneforcidine.

(-)- and (+)-Geissman-Waiss lactone, 4b, was efficiently prepared via the intramolecular C-H insertion reaction of the chiral nonracemic diazoacetates (-)-5a and (+)-5b catalyzed by dirhodium(II) tetrakis[methyl (5R and 5S)-3-phenylpropanoyl-2-imidazolidinone-5-carboxylate]. The cyclization was found to proceed with excellent regioselectivity and cis-diastereoselectivity. The bicyclic lactone (-)-4b was successfully used in the synthesis of the necine base, (-)-turneforcidine 2.     

Alpha-phosphono lactone analogues of farnesyl pyrophosphate: an asymmetric synthesis via ring-closing metathesis

An alpha-phosphono lactone derivative of farnesol has been prepared, in both racemic and nonracemic forms, to provide a new type of farnesyl pyrophosphate analogue. Attempted preparation of the racemic alpha-phosphono lactone through rearrangement of a vinyl phosphate derived from the parent lactone resulted in both rearrangement and lactone ring opening, revealing that the farnesyl lactone was not stable to the excess of strong base required for the rearrangement. A procedure for C-P bond formation based on generation of the lactone enolate, reaction with a P(III) reagent, and oxidation was successful in providing the racemic alpha-phosphono lactone, in part, because only 1 equiv of strong base was required. The same strategy for phosphonate synthesis then was applied to the nonracemic farnesyl lactone, prepared through a sequence including allylation of farnesal with a nonracemic borane reagent, reaction of the product alcohol with acryloyl chloride, and formation of an unsaturated lactone through ring-closing metathesis. A similar strategy gave the corresponding racemic alpha-phosphono lactam through a six-step sequence from farnesal.     

Stereoselective synthesis of the cytotoxic macrolide aspergillide B

A total, stereoselective synthesis of the cytotoxic macrolide aspergillide B has been performed. A cross metathesis and a C-glycosidation via a Mukaiyama-type aldol reaction were key features of the synthesis. The macrocyclic lactone ring was created by means of the Yamaguchi procedure.