Synthesis of the oxindole alkaloid (−)-horsfiline

Pellegrini, Claudio; Strässler, Christoph; Weber, Michael; Borschberg, Hans‐Jürg

doi:10.1016/s0957-4166(00)86273-4

Cited by 93 publications

(34 citation statements)

References 21 publications

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“…[21] (for reviews, see [22]), the great ease with which compounds 2,12,13, and 22 epimerize, seems to be unprecedented. During the reductive decyanation of (+)-33 in a recent synthesis of (-)-horsfiline ((-)-34), e.g., less than 5% of racemization was observed [8] (Scheme 5), while (-)-11 racemized and epimerized completely under the same conditions. The marked difference in stability between (+)-2 and (-)-34 is caused conceivably by the presence of the isobutyl side chain which probably destabilizes the spiro form and in turn renders the retro-Mannich intermediates I and 111 more stable as compared to VII.…”

mentioning

confidence: 99%

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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mentioning

confidence: 99%

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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“…F.v.p. of compounds (16)- (18) gave small amounts of pyrolysates containing the 3-methylidene compound (19), but polymerization was extensive and we concluded, as did Palmisano and coworkers, 16 that compound (19) is not a practical precursor of horsfiline.…”

Section: Cycloaddition Of Nitrogen Ylides To 3-methylideneindolin-2-onementioning

confidence: 51%

“…Horsfiline (4) has been a popular synthetic target, and successful strategies have included radical cyclization, 17 oxidative ring contraction of a ␥-carboline 18 or of a chiral ␤-carboline ester, 19 internal Mannich cyclization of an oxindole derived from 5-methoxytryptamine 18 and finally cycloaddition of the ylide (11) to the substituted methylideneindolin-2-one (20), in which the ester group serves both to increase the reactivity of the C=C bond as a dipolarophile and to stabilize (20) against polymerization. 16 The necessity for later removal of the carboxy group is compensated by the high initial yields, and by the capacity for chiral synthesis using (20) with R = (+)-or (-)-menthyl.…”

Section: Cycloaddition Of Nitrogen Ylides To 3-methylideneindolin-2-onementioning

confidence: 99%

An Approach to Some Spiro Oxindole Alkaloids Through Cycloaddition Reactions of 3-Methylideneindolin-2-one

Bell¹,

Brown²,

Eastwood³

et al. 2000

Aust. J. Chem.

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3-Methylideneindolin-2-one (3-methylideneoxindole) (1) was prepared in 60–89% yield by flash vacuum pyrolysis of the acetate or methyl carbonate of 3-hydroxy-3-methylindolin-2-one, and was fully characterized, but application of the same procedure to 3-hydroxy-5-methoxyindolin-2-one did not give useful yields. Cycloaddition reactions of CH2= +NR–CH2 – and of the related ylide (25) (from 1-(trimethylsilylmethyl)piperidine-2-carbonitrile and AgF) to 3-methylideneindolin-2-one (1) gave 4–20% yields of spiro oxindoles, but yields were markedly below those achieved in cycloadditions to the more electrophilic N-phenylmaleimide (70–79%). Attempted alkylation of weakly basic secondary amines, e.g. piperidine-2-carbonitrile, with Me3SiCH2Cl in dimethyl sulfoxide/K2CO3 gave only carbamates Me3SiCH2OOCNR2.

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“…On the other hand, a clear NOE between H-9 and H-3 was observed in the differential NOE experiment of 57a, revealing its 7(S) configuration. The predominant formation of diastereomeric oxindole derivatives through the lead tetraacetate oxidation/solvolytic rearrangement may be interpreted from the plausible mechanism discussed in previous papers [27][28][29][30]. In contrast, the facile interconversion of rhynchophylline (6) and isorhynchophylline (8) under acidic conditions is well known [24,[31][32][33].…”

Section: -2 Alkaloids In Uncaria Attenuatamentioning

confidence: 85%

Chemistry of Indole Alkaloids Related to the Corynanthe-Type from Uncaria, Nauclea and Mitragyna Plants

Takayama¹,

Kitajima²,

Kogure

2005

COC

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A number of monoterpenoid indole and oxindole alkaloids have been isolated from botanical sources, and many of them have been found to possess significant pharmacological activities and are utilized as key lead compounds in new drug development. In this review, the recent results of our phytochemical and synthetic studies of indole alkaloids having the Corynanthe-type related skeleton from genera Uncaria, Nauclea, and Mitragyna, which are classified under tribe Cinchoneae, family Rubiaceae, are described.

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Synthesis of the oxindole alkaloid (−)-horsfiline

Cited by 93 publications

References 21 publications

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

An Approach to Some Spiro Oxindole Alkaloids Through Cycloaddition Reactions of 3-Methylideneindolin-2-one

Chemistry of Indole Alkaloids Related to the Corynanthe-Type from Uncaria, Nauclea and Mitragyna Plants

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