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1.
The enantioselective synthesis of indolizidines (−)-203A, (−)-209B, (−)-231C, (−)-233D, and (−)-235B″ has been achieved and the absolute stereochemistry of both indolizidines 203A and 233D was established as 5S,8R,9S. The relative stereochemistry of natural 231C was established by the present asymmetric synthesis. 相似文献
2.
Miguel A. González 《Tetrahedron letters》2004,45(26):5039-5041
The first synthesis of 5-isopropenyl-3-methyl-cyclohex-2-enone, (isocarvone) (2), in enantiomerically pure form is reported. Both enantiomers of 2 can be produced by manipulation of carboxylic acid 5, which is available from R-(−)-carvone (1). These materials provide new chiral building blocks that could be used in total synthesis of natural products and related optically active compounds. 相似文献
3.
Nobuhiro Maezawa 《Tetrahedron letters》2007,48(28):4865-4867
The synthesis of a novel sphingosine kinase inhibitor, (−)-F-12509A ((−)-1), was achieved in a highly efficient manner that included nine longest linear steps and 45% overall yield from (−)-bicyclic β-ketoester (−)-2, and its absolute configuration was determined to be (5S,9S,10S). 相似文献
4.
Toru TachiharaTakeshi Kitahara 《Tetrahedron》2003,59(10):1773-1780
Enantioselective total synthesis of (+)-epiepoformin 1, (+)-epiepoxydon 2 and (+)-bromoxone 3 using a chiral building block, ethyl (1R,2S)-5,5-ethylenedioxy-2-hydroxycyclo- hexanecarboxylate 6, is described. Since the synthesis afforded intermediates 18, 2 and 25, it accomplished a formal synthesis of (−)-theobroxide 19, (−)-phyllostine 22, (+)-herveynone 27 and (−)-asperpentyn 28. The usefulness of 6 for the synthesis of natural epoxycyclohexene derivatives was demonstrated. 相似文献
5.
Pinki PalArun K. Shaw 《Tetrahedron》2011,67(22):4036-4047
Stereoselective total syntheses of aggregation pheromones (+)-exo-brevicomin (9a), (−)-exo-brevicomin (9b), (+)-endo-brevicomin (9c), (−)-endo-brevicomin (9d) and styryllactones (+)-cardiobutanolide (14a), (−)-cardiobutanolide (14b), and (+)-goniofufurone (19a) were achieved in good yields from enantiomerically pure highly functionalized furanoid glycal building blocks (1a-d) involving similar synthetic strategies, thus making these furanoid glycals highly useful building blocks in diversity-oriented synthesis (DOS). 相似文献
6.
The first synthesis of the fungal natural product (−)-xylariamide A 1 is reported. N,O-Bis(trimethylsilyl)acetamide induced coupling of d-tyrosine with (E)-but-2-enedioic acid 2,5-dioxo-pyrrolidin-1-yl ester methyl ester 5 produced the dechloro natural product 6, which was subsequently monochlorinated using oxone and KCl to yield synthetic 1. (−)-Xylariamide A 1, (+)-xylariamide A 2 and (−)-dechloroxylariamide A 6 displayed no cytotoxic or antimicrobial activity. 相似文献
7.
Takashi Kouko 《Tetrahedron》2005,61(9):2309-2318
The total synthesis of the marine bisindole alkaloids, (+)-hamacanthins A (2a) and B (2b), and (−)-antipode of cis-dihydrohamacanthin B (2e) was achieved by transamidation-cyclization of N-(2-aminoethyl)-2-oxoethanamide 18 derived from (S)-indolylglycinol 10. 相似文献
8.
The concise synthesis of (8aR)-(−)-albaconol (1) from (8aR)-albicanol (2) obtained from the lipase-assisted asymmetric acetylation of rac-2, was achieved in 45% overall yield (eight steps). By comparison of the sign of specific rotation of between synthetic (8aR)-(−)-albaconol (1) and natural (+)-albaconol (1), the absolute structure of natural (+)-1 was determined to be 1R,2R,4aS,8aS configuration. 相似文献
9.
(±)-(4,5-anti)-4-Benzyloxy-5-hydroxy-(2E)-hexenoic acid 6 was subjected to δ-lactonization in the presence of 2,4,6-trichlorobenzoyl chloride and pyridine to give the α,β-unsaturated-δ-lactone congener (±)-7 (87% yield) accompanied by trans-cis isomerization. This δ-lactonization procedure was applied to the chiral synthesis of (+)-(4S,5R)-7 or (−)-(4R,5S)-7 from the chiral starting material (+)-(4S,5R)-6 or (−)-(4R,5S)-6. Deprotection of the benzyl group in (+)-(4S,5R)-7 or (−)-(4R,5S)-7 by the AlCl3/m-xylene system gave the natural osmundalactone (+)-(4S,5R)-5 or (−)-(4R,5S)-5 in good yield, respectively. Condensation of (−)-(4R,5S)-5 and tetraacetyl-β-d-glucosyltrichloroimidate 22 in the presence of BF3·Et2O afforded the condensation product (−)-8 (97% yield), which was identical to tetra-O-acetylosmundalin (−)-8 derived from natural osmundalin 9. 相似文献
10.
Aisling O’ByrneSteven O’Reilly Catherine TighePaul Evans Laura CiuffiniM. Gabriella Santoro 《Tetrahedron letters》2012,53(44):5936-5938
A stereocontrolled synthesis of the marine natural products (+)-bromoxone (1) and (+)-4-acetylbromoxone (2) is reported. The sequence features the enzymatic kinetic resolution of 4-hydroxycyclohexenone (6) via its S-benzyl adduct. Thereafter, a base-mediated elimination-silylation generated an optically active (−)-4S-4-tert-butyldimethylsilyoxycyclohexenone (5), which then underwent diastereoselective epoxidation. Saegusa-Ito oxidation enabled formation of the corresponding α,β-unsaturated ketone 13. Bromination-elimination and subsequent removal of the silicon protecting group afforded (+)-bromoxone (1) which was converted into (+)-(4S,5R,6R)-4-acetoxy-2-bromo-5,6-epoxycyclohex-2-enone (2) [(+)-4-acetylbromoxone]. Using a luciferase gene reporter assay ED50 for NFκB inhibition of 9 μM was determined. 相似文献
11.
The diastereoselective PdCl2/CuCl2-catalysed intramolecular methoxyaminocarbonylation of N-benzyl protected alkenyl amine 4 was used as a key step in the total synthesis of the naturally occurring piperidine alkaloid (−)-pinidinone. Commercially available (S)-propylene oxide was employed as starting material, delivering the key substrate 4 in three steps and 68% overall yield. Subsequently, the influence of various reaction parameters on the diastereoselectivity of the key cyclisation of 4 was scrutinised. Copper(II) chloride proved to be the optimum reagent and/or co-catalyst for the successful aminocyclisation-methoxycarbonylation tandem transformation of alkenyl amine 4 into the desired methyl esters 3 and 8. The latter were subsequently transformed into the title natural product. 相似文献
12.
Xinyuan Zhang 《Tetrahedron letters》2010,51(29):3840-3842
Five products were yielded from the transformation of (−)-Huperzine A (1) by Streptomyces griseus CACC 200300. Their structures were determined as 16-hydroxyl huperzine A (2), 14α-hydroxyl huperzine A (3), huperzine A 8α,15α-epoxide (4), 13N-formyl huperzine A (5), and 13N-acetyl huperzine A (6) on the basis of their chemical and physical data. It is the first report on the microbial transformation of (−)-Huperzine A and would facilitate further structural modification by chemo-enzymatic method. 相似文献
13.
E.J. Alvarez-Manzaneda R. Chahboun E. Cabrera Torres R. Alvarez-Manzaneda 《Tetrahedron letters》2005,46(32):5321-5324
A short and efficient synthesis of the rearranged nor-sesquiterpenes (+)-austrodoral (1) and (+)-austrodoric acid (2), recently isolated from the Antarctic marine mollusk Austrodoris kerguelenensis, from diterpene (−)-sclareol (4) is reported. The key step of the sequence is the pinacol rearrangement of the drimanetriol 11. 相似文献
14.
We describe the efficient formal syntheses of both natural (−)-aphanorphine and unnatural (+)-aphanorphine from the same commercially available amino acid, (2S,4R)-4-hydroxyproline. The tricyclic framework was constructed by intramolecular Friedel-Crafts reaction. (1R,4S)-1-Methyl-8-methoxy-3-(4-toluenesulfonyl)-2,3,4,5-tetrahydro-1,4-methano-3-benzazepine (8) was synthesized in six steps from sulfonamide 3; (−)-aphanorphine methyl ether 24 was obtained in seven steps from lactone 10. Intramolecular etherification of 18 proceeded with excellent stereoselectivity in the presence of BF3·OEt2, which has paved an efficient synthetic route to a series of medicinally attractive heterocycles. 相似文献
15.
Nicolas Robert 《Tetrahedron》2007,63(18):3702-3706
A concise enantiopure synthesis of six monoterpenic alkaloids of the actinidine series possessing a cyclopenta[c]pyridine skeleton, (+)-deoxyrhexifoline (4), (+)-boschniakinic acid (5), (+)-boschniakine (6), (−)-plantagonine (7), (−)-indicaine (8) and (−)-tecostidine (9) is reported starting with the chiral precursor 3-bromo-5-((4R)-phenyloxazolin-2-yl)pyridine (10). It involves a C-4 regioselective connection of a butene appendice and an intramolecular 5-exo-trig Heck annulation sequence followed by hydrogenation of the exocyclic alkene. Mixture of (3R)- and (3S)-7-((4R)-phenyloxazolin-2-yl)cyclopenta[c]pyridines was separated by HPLC before being transformed into enantiopure natural products (4-9) by modification of the oxazoline group. 相似文献
16.
Satoshi ImutaShinya Ochiai Miho KuribayashiNoritaka Chida 《Tetrahedron letters》2003,44(27):5047-5051
The total synthesis of (−)-actinobolin 2, an antipode of the natural product starting from d-glucose is described. A three-component coupling reaction of a functionalized cyclohexenone (+)-6, derived from d-glucose by way of Ferrier's carbocyclization, with vinyl cuprate and an aldehyde (R)-5 effectively constructed the carbon framework of 2 in a highly stereoselective manner. The formal synthesis of the natural enantiomer 1 from d-glucose was also achieved. 相似文献
17.
Enrique Alvarez-Manzaneda Rachid Chahboun Esteban Alvarez Mohammed Hmamouchi 《Tetrahedron letters》2007,48(50):8930-8934
A new route to abietane and podocarpane-type terpenoids from labdane diterpenes is reported. The key step is the transformation of β-ketoester 9 into the corresponding O-acetylsalicylate ester 18, via a manganese(III)-based oxidative free-radical cyclization carried out in Ac2O. Utilizing this, the synthesis of the antitumor (+)-7-deoxynimbidiol (5) from (−)-sclareol (11) has been achieved. (+)-Nimbidiol (6) and the natural terpenoid 20 have also been synthesized. 相似文献
18.
The enantioselective total synthesis of (−)-quinolactacin B (−)-1 was performed in seven steps and 33% overall yield from tryptamine. The synthesis features the use of ruthenium catalytic asymmetric hydrogen reaction to introduce the chirality in dihydro-β-carboline 2. Based on Noyori’s work, the hydrogenation using the (R,R)-TsDPEN-Ru complex produces dihydro-β-carbolines possessing the (S) absolute configuration, the corrected asymmetric center of the natural product. The synthetic quinolactacin B displayed optical rotations that was in accordance with that of the natural product, thereby supporting the (S) configuration for natural quinolactacin B. The final product’s stereochemical assignment is in agreement with that proposed by Nakagawa and co-workers. 相似文献
19.
The asymmetric Michael addition of propionaldehyde to (2E)-(3-nitro-but-2-enyloxymethyl)-benzene 8, catalyzed by the chiral diamine (S,S)-N-iPr-2,2′-bipyrrolidine, afforded, with 93% ee, a precursor 9 of (−)-botryodiplodin. The nitro functionality of 9 was converted to a ketone via a Nef reaction to give, after a few steps, the enantiomerically enriched (−)-botryodiplodin. 相似文献
20.
Shin-ichi NayaMakoto Nitta 《Tetrahedron》2003,59(21):3709-3718
Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac2O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The 13C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol−1 by the variable temperature 1H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF4− and 12a-c·BF4−) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF4−) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF4/Ac2O afforded two kinds of novel products 11a-c·BF4− and 12a,c·BF4− in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF4− and 12a-c·BF4− observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF4− and 12a-c·BF4− were studied, and structural characterization of 11c·BF4− based on the X-ray crystal analysis and MO calculation was also performed. 相似文献