Synthetic approaches to fumitremorgins. III. Synthesis of optically active pentacyclic ring systems, and their oxidation at ring C.

Nakagawa, Masako; Fukushima, Hiroshi; Kawate, Tomohiko; Hongu, Mitsuya; Une, Teruaki; Kodato, Shinichi; Taniguchi, Mikio; Hino, Tohru

doi:10.1248/cpb.37.23

Cited by 25 publications

(17 citation statements)

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“…of 0.80 g (2.79 mmol) of (-)-4 [9] in 30 ml of 1,4-dioxane and 1.6 ml of pyridine were added 0.43 ml(3.07 mmol) of (CF,CO),O with efficient stirring at 5". After 30 min, the mixture was worked up as usual to give 1.00 g (94%) of (+)-6 after chromatography (20 g of silica gel, AcOEt/p.e.…”

Section: Syntheses ( I S3 S J -Methyl I 234-tetrah-vdro-i-(2-metmentioning

confidence: 99%

“…General Procedure A , starting with 3.0 g (10.5 mmol) of (-)-4 [9], followed by chromatography (silica gel, AcOEt/p.e. 1:9+1:4) produced 3.12 g(90%) of(+)-7.…”

Section: (19) 265 (29) 169 (22) 168 (23) 156 (10)mentioning

confidence: 99%

“…[3,4-b]indole-3-carbonitrile ((+)-S). As described above, starting with (+)-5 [9] (5)), 3.55 (H-N(5')), 2.26 (H,,,,,-C(7')), 1.1X and 0.92 (2 H-C(8')); 2.26 (H,,,,,-C(7')) +7.30 (H-C(4)), 2.85 (HCl,?-C(7')); 2.85 (Hczy-C(7'))+ 4.12 (H-C(6)), 2.26 (H,,,,,-C(7')); 4.12 (H-C (6) 21.8 (q). MS: 287 (65, M'), 243 (49), 199 (20), 185 (11).…”

Section: (19) 265 (29) 169 (22) 168 (23) 156 (10)mentioning

confidence: 99%

“…In the is0 series both of them are shielded relative to their counterparts in the epimeric series by the aromatic z-system laying beneath, and this holds especially for the corresponding low-field branch which is arbitrarily named HA-C(8'). The "C-NMR spectra of the epimeric pairs are very similar (Table 2) [9] (not included in Exper. Part). '…”

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confidence: 93%

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Total Synthesis of (+)‐Elacomine and (−)‐Isoelacomine, Two Hitherto Unnamed Oxindole Alkaloids from Elaeagnus commutata

Pellegrini¹,

Weber

Borschberg³

1996

Helvetica Chimica Acta

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Racemic elacomine ((%)-2), a hemiterpene spiro oxindole alkaloid from Elueagnus commutata, was synthesized in five steps from 6-methoxytryptamine (19) in 16% overall yield (Scheme 3 ) . The final oxidative rearrangement of the corresponding 8-carboline precursor (%)-21 furnished isoelacomine ((%)-22) as a by-product (6% overall yield). A more elaborate route that started from L-tryptophan furnished (+)-2 and (-)-22 with optical purities of 76% (Scheme 4 ) and established the absolute configuration of these compounds. A reinvestigation of the alkaloidal content of the roots of E. cornmututu showed that both elacomine and isoelacomine occur naturally in racemic form. ( [ a ] , = +174.8) hemiterpene oxindole alkaloid3) from the roots of the shrub Elaeagnus commutata (Elaegnaceae) [ 11. Chemical degradation studies and spectroscopic evidence led to structure proposal 1 which, however, left open the exact position of the phenolic OH group and the relative configuration at the two asymmetric centres C(3) and C(4')4). These questions were addressed subsequently by James and Williams by means of an X-ray diffraction study that allowed them to established formula 2 for this compound which they had obtained from Locock and Slywka [2]. Curiously enough, the sample investigated by X-ray crystallography must have been racemic, since the crystal was composed of alternating layers of both optical antipodes of 2, a fact that is consistent with the reported space group P2,lc. Surprisingly, the evident conflict concerning the enantiomeric purity of 2 was not commented by James and Williams, and in the context of our interest in the chemo-and diastereoselective transformation of indole alkaloids into their oxindole (1,3-dihydro-2H-indol-2-one) or pseudoindoxyl (1,2-dihydro-3H-indo1-3-one) derivatives [4-81, we decided to synthesize (+)-elacomine ((+)-2) in a way that would allow to delineate its hitherto unknown absolute configuration. Introduction. ~ In 1968, Slywka reported the isolation of a novel, optically active

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Section: Syntheses ( I S3 S J -Methyl I 234-tetrah-vdro-i-(2-metmentioning

confidence: 99%

“…General Procedure A , starting with 3.0 g (10.5 mmol) of (-)-4 [9], followed by chromatography (silica gel, AcOEt/p.e. 1:9+1:4) produced 3.12 g(90%) of(+)-7.…”

Section: (19) 265 (29) 169 (22) 168 (23) 156 (10)mentioning

confidence: 99%

Section: (19) 265 (29) 169 (22) 168 (23) 156 (10)mentioning

confidence: 99%

mentioning

confidence: 93%

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Total Synthesis of (+)‐Elacomine and (−)‐Isoelacomine, Two Hitherto Unnamed Oxindole Alkaloids from Elaeagnus commutata

Pellegrini¹,

Weber

Borschberg³

1996

Helvetica Chimica Acta

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“…This method has an advantage in that the reaction can be carried out without the isolation of the acid-labile imines under a one-pot procedure. Although the Pictet-Spengler reactions using tryptophan and aldehydes which produce chiral 1,3-disubstitued 1,2,3,4-tetrahydro-b-carbolines (THbCs) have been extensively investigated, [6][7][8][9][10][11][12] the reaction with ketone has not been hitherto investigated. Here we describe the Pictet-Spengler reaction of tryptophan methyl ester with aryl methyl ketones, which may provide a convenient method of synthesizing chiral 1,1,3-trisubstituted THbCs.…”

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confidence: 99%

A Synthesis of Chiral 1,1,3-Trisubstituted 1,2,3,4-Tetrahydro-β-carbolines by the Pictet–Spengler Reaction of Tryptophan and Ketones: Conversion of (1R,3S)-Diastereomers into Their (1S,3S)-Counterparts by Scission of the C(1)–N(2) Bond

Horiguchi¹,

Nakamura²,

Saitoh³

et al. 2003

Chem. Pharm. Bull.

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The Pictet-Spengler reaction 1) has long been an important reaction for the syntheses of biologically important isoquinolines and b-carbolines.2,3) Recently, we have developed a highly efficient method of synthesizing 1,1-disubstituted tetrahydroisoquinolines 4) and tetrahydro-b-carbolines 5) by the Pictet-Spengler reaction of arylethylamines and ketones using titanium(IV) isopropoxide as an iminating reagent. This method has an advantage in that the reaction can be carried out without the isolation of the acid-labile imines under a one-pot procedure. Although the Pictet-Spengler reactions using tryptophan and aldehydes which produce chiral 1,3-disubstitued 1,2,3,4-tetrahydro-b-carbolines (THbCs) have been extensively investigated, [6][7][8][9][10][11][12] the reaction with ketone has not been hitherto investigated. Here we describe the Pictet-Spengler reaction of tryptophan methyl ester with aryl methyl ketones, which may provide a convenient method of synthesizing chiral 1,1,3-trisubstituted THbCs. Results and DiscussionsPictet-Spengler Reaction of Tryptophan Methyl Ester (1) with Aryl Methyl Ketones (2) The condensation reaction of L-tryptophan methyl ester (1) and aryl methyl ketones (2a: acetophenone, 2b: 1-(4-chlorophenyl)-2-ethanone, 2c: 1-(4-methoxyphenyl)-2-ethanone) to the imine intermediates (3a-c) was carried out by heating in titanium(IV) isopropoxide at 70°C for 3 h without using any solvent. To the mixture of the in situ formed imines (3) was added a large excess amount of trifluoroacetic acid (TFA) or formic acid (HCOOH). The reaction mixture was then allowed to react at 70°C or at room temperature for appropriate times to complete the Pictet-Spengler cyclization. During the imination, the ester exchange reaction from the methyl ester to the isopropyl ester occurred. The reactions, in all cases, produced two diastereometric 1-aryl-3-isopropoxycarbonyl-1-methylTHbCs (4) and (5) in good total yields (Chart 1, Table 1).

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A Reinvestigation of the Oxidative Rearrangement of Yohimbane‐Type Alkaloids. Part B. Formation of Oxindol (= 1,3‐Dihydro‐2H‐indol‐2‐one) Derivatives

Stahl¹,

Borschberg

Acklin

1996

Helvetica Chimica Acta

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The methanolysis of the epimeric 7-chloro-7H-yohimbine derivatives 2 and 3 was reinvestigated. In case of the 7a-epimer 2, the reaction was uneventful and conformed with earlier observations, i.e., under sufficiently mild conditions, only the imino ether 4 ( = imino ether A) was produced. Under the same conditions, the less reactive p-isomer 3 furnished a mixture of both imino ethers 4 and 5, accompanied by the elimination product 11, and by equal amounts of yohimbine (1) and 3,4,5,6-tetradehydroyohimbine (12), which are believed to arise through a disproportionation process of the putative intermediate 5,6-didehydroyohimbine (23). The nature of this divergent reactivity and of the ready equilibration of 4 and 5 was investigated by means of extensive force-field and semi-empirical calculations (AM1 and PM3) of various conformers of the compounds 2-5 and of some possible reaction intermediates.

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Synthetic approaches to fumitremorgins. III. Synthesis of optically active pentacyclic ring systems, and their oxidation at ring C.

Cited by 25 publications

References 1 publication

Total Synthesis of (+)‐Elacomine and (−)‐Isoelacomine, Two Hitherto Unnamed Oxindole Alkaloids from Elaeagnus commutata

Total Synthesis of (+)‐Elacomine and (−)‐Isoelacomine, Two Hitherto Unnamed Oxindole Alkaloids from Elaeagnus commutata

A Synthesis of Chiral 1,1,3-Trisubstituted 1,2,3,4-Tetrahydro-β-carbolines by the Pictet–Spengler Reaction of Tryptophan and Ketones: Conversion of (1R,3S)-Diastereomers into Their (1S,3S)-Counterparts by Scission of the C(1)–N(2) Bond

A Reinvestigation of the Oxidative Rearrangement of Yohimbane‐Type Alkaloids. Part B. Formation of Oxindol (= 1,3‐Dihydro‐2H‐indol‐2‐one) Derivatives

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