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At least 163 records · Page 9Linked to original sources
PubMed1983

Do planar alkaloids from Strychnos usambarensis intercalate into the DNA helix?

The mode of binding of melinonine F and normelinonine F to DNA has been investigated through physico-chemical methods which proved most valuable in the study of dye-DNA interactions, namely absorption spectrophotometry, circular and linear dichroism, fluorescence polarization, viscosity increase of linear DNA and circular DNA unwinding. The spectroscopic properties resembled those observed with planar heterocyclic compounds intercalating between the DNA base pairs: bathochromic shift and hypochromism in the ligand absorption bands; presence of a strong binding process with an association constant of the order of 10(6)M-1 and a number of binding sites of 0.1 to 0.15; appearance of extrinsic optical activity in the ligand absorption bands with a dependence on the binding ratio typical for an excitonic origin; negative reduced electric dichrosim of the ligand chromophore of the same order of magnitude as that of the DNA heterocyclic bases. However the increase of the length of sonicated DNA determined from viscosity changes was much smaller than for most intercalating compounds and no unwinding of PM2 circular DNA was detected.

Alkaloids↗
PubMed2001

Biogenetically inspired approach to the Strychnos alkaloids. Concise syntheses of (+/-)-akuammicine and (+/-)-strychnine.

A linear synthesis of the indole alkaloid (+/-)-akuammicine (2) was completed by a novel sequence of reactions requiring only 10 steps from commercially available starting materials. The approach features a tandem vinylogous Mannich addition and an intramolecular hetero Diels-Alder reaction to rapidly assemble the pentacyclic heteroyohimboid derivative 8 from the readily available hydrocarboline 6. Oxidation of the E ring of 8 gave the lactone 9 that was converted into deformylgeissoschizine (11). The subsequent elaboration of 11 into 2 was effected by a biomimetically patterned transformation that involved sequential oxidation and base-induced skeletal reorganization. A variation of these tactics was then applied to the synthesis of the C(18) hydroxylated akuammicine derivative 36. Because 36 had previously been converted into strychnine (1) in four steps, its preparation constitutes a concise, formal synthesis of this complex alkaloid.

Alkaloids↗
PubMed2003

A novel and general synthetic pathway to strychnos indole alkaloids: total syntheses of (-)-tubifoline, (-)-dehydrotubifoline, and (-)-strychnine using palladium-catalyzed asymmetric allylic substitution.

A method of palladium-catalyzed asymmetric allylic substitution for synthesizing 2-substituted cyclohexenylamine derivatives was established. Treatment of a 2-silyloxymethylcyclohexenol derivative with ortho-bromo-N-tosylaniline in the presence of Pd(2)dba(3).CHCl(3) and (S)-BINAPO in THF afforded a cyclohexenylamine derivative with 84% ee in 80% yield. The Heck reaction was carried out to produce an indolenine derivative in good yield. Using this method, we synthesized indolenine derivative 7, which was recrystallized from EtOH to give an optically pure compound. From this compound, tetracyclic ketone 13, which should be a useful intermediate for the synthesis of indole alkaloids, could be synthesized. The total syntheses of (-)-dehydrotubifoline, (-)-tubifoline, and (-)-strychnine were achieved from 13. All ring constructions for the syntheses of these natural products were achieved using a palladium catalyst.

Allyl Compounds↗
PubMed1996

Syntheses of Strychnos and Aspidospermatan-Type Alkaloids. 8. Selective Total Syntheses of Mossambine and 14-epi-Mossambine by a Radical Cyclization Reaction(1).

Mossambine (6) was obtained by a six-step reaction sequence from the indoloazepine ester 7. Radical cyclization of the tetracyclic vinyl iodide 12a provided a racemic pentacyclic ketone 16E, which could be converted to either enantiomer by condensation with (S or R)-N,S-dimethyl-S-phenylsulfoximine and selective pyrolysis of the resulting diastereomeric alcohols 18 and 19 or 20 and 21. Selective reductions of the resolved (or racemic) ketone 16E provided mossambine (6) and its hydroxy epimer 17.

Journal Article↗
PubMed2001

A new and general synthetic pathway to strychnos indole alkaloids: total syntheses of (-)-dehydrotubifoline and (-)-tubifoline by palladium-catalyzed asymmetric allylic substitution.

[see reaction]. A novel procedure for the synthesis of an indole skeleton was developed. Treatment of a cyclohexenol derivative having a silyloxymethyl group at the 2-position with N-tosyl-o-bromoaniline in the presence of Pd2dba3*CHCl3 and (S)-BINAPO gave compound 6a with 84% ee in 75% yield. Compound 6a was converted into 11, which was treated with Pd(OAc)2 and Me(2)PPh in the presence of Ag2CO3 to give indoline derivative 12. From 12, we succeeded in the total syntheses of (-)-dehydrotubifoline and (-)-tubifoline.

Alkaloids↗