A Survey of Recently Discovered Naturally Occurring Organohalogen Compounds

Gribble, Gordon W.

doi:10.1021/acs.jnatprod.3c00803

Cited by 4 publications

(2 citation statements)

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“…The rauvomines ( 1 – 7 , Figure A) are a group of indole alkaloids recently isolated from Rauvolfia vomitoria, a small tree used in various traditional medicines which has proven to be a rich source of monoterpene indole alkaloids (MIAs). , Structurally, rauvomines A–G fall into the sarpagine class of MIAs (exemplified by 8 ) but contain certain features that render them unique among this family . For instance, while all rauvomines incorporate an additional C-19 methyl-bearing stereocenter found in a smaller subset of the class, rauvomines A ( 1 ) and C ( 3 ) contain an alkyl chloride, an uncommon motif for terrestrial indole alkaloids . Rauvomine B ( 2 ) is more unique still, with its proposed structure featuring a cyclopropane ring bridging its indoloquinolizidine unit, formed via an additional C–C bond between C-16 and C-20 in the typical sarpagine scaffold.…”

Section: Introductionmentioning

confidence: 99%

Total Synthesis of (−)-Rauvomine B via a Strain-Promoted Intramolecular Cyclopropanation

Aquilina,

Banerjee,

Morais

et al. 2024

J. Am. Chem. Soc.

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We describe the first total synthesis of the unusual cyclopropane-containing indole alkaloid (−)-rauvomine B via a strategy centered upon intramolecular cyclopropanation of a tetracyclic N-sulfonyltriazole. Preparation of this precursor evolved through two generations of synthesis, with the ultimately successful route involving a palladium-catalyzed stereospecific allylic amination, a cis-selective Pictet−Spengler reaction, and ring-closing metathesis as important bond-forming reactions. The key cyclopropanation step was found to be highly dependent on the structure and conformational strain of the indoloquinolizidine Nsulfonyltriazole precursor, the origins of which are explored computationally through DFT studies. Overall, our synthesis proceeds in 11 total steps and 2.4% yield from commercial materials.

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Section: Introductionmentioning

confidence: 99%

Total Synthesis of (−)-Rauvomine B via a Strain-Promoted Intramolecular Cyclopropanation

Aquilina,

Banerjee,

Morais

et al. 2024

J. Am. Chem. Soc.

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“…Mixed polyhalogenated (interhalogen) natural products are mainly marine-derived; their provenance is mostly from Rhodophycae (red algae), but some are also produced by Porifera (sponges). , Most of the 8000 or more reported halogenated marine natural products are brominated, and about 700 have both Cl and Br in their structures. Of these compounds, the polyhalogenated monoterpene halomon ( 1a )containing a vicinal bromochloro isoprenyl group (hereafter referred to as VBC) from Portieria hornemannii reported in 1975 by the Moore group in Hawaiidrew renewed interest from the National Cancer Institute in the early 1990s with the discovery of its potent antiproliferative activity against cultured human cancer cells lines and expression of highly differential activities within the standard NCI cultured cancer cell panel (NCI-60) …”

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confidence: 99%

Empirical Chiroptical Analyses of Vicinal Bromochloro Natural Products by van’t Hoff’s Principle of Optical Superposition: Assignment of the C-16 Configurations of Callophycols A and B

Molinski

2024

J. Org. Chem.

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A simple empirical method is described that allows the assignment of absolute configurations of natural products containing chiral vicinal bromochloro (VBC) units, including the bromochloro substituted isoprenyl units present in the structures of antiproliferative halomon (1a) and its halogen-swapped isomer iso-halomon (1b) from the red alga, Portieria hornemannii, and callophycols A (3) and B (4) from Callophycus serratus. The relative configurations of 3 and 4, published in 2007, were incomplete: C-16 was left unassigned. It is now shown that the additivity of molar rotations, [M]D (herein, abbreviated [M])a consequence of van’t Hoff’s principle of optical superpositioncould be used to deconvolute rotatory contributions, designated as [M X] and [M Y] of the two remotely spaced chiral substructures within 3 and 4 using simple arithmetic. Input of proxy values, [M Y1 ] and [M Y2 ], for the two different VBC units in two equations for [M X] and application of a “conditional test” returns the same value for [M X] only when a proxy with the correct configuration is included. It is revealed that 3 and 4 have opposite configurations at the C-16 stereocenter: 16S and 16R, respectively. Two important implications lie in these findings: 3 and 4 appear to qualify as paired-regioisomers, coupled through a putative dyotropic rearrangement (DR), and the biosyntheses of other Callophycus secondary metabolites, now numbering over 50, are tightly controlled by stereoelectronic considerations including neighboring group interactions of the DR. It now appears, counter to earlier suggestions, that the chirality of Callophycus secondary metabolites, despite their high chemodiversity, are surprisingly highly conserved. Enantiofacial halogenation additions to the CC double bonds of precursor alkenes appear to direct the formation of the remaining stereocenters at both the halogenated benzoate-decalin core and the distal VBC of 3 and 4. A consistent hypothesis is proposed to account for macrolactonizations in other Callophycus natural products including bromophycolides A and B. The conditional test of molar rotations was applied in a different context to understand the chiroptical properties and trends observed in the highly iodinated meroditerpenes, iodocallophycols A–E, also from Callophycus sp., resulting in the revision of the configuration of callophycol E from (10R,14R) to (10S,14S).

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