Two‐dimensional NMR spectra of asbestinin diterpenes isolated from <i>Briareum asbestinum</i> (Pallas). Total stereochemical assignment by two‐dimensional NMR techniques

Rodrı́guez, Abimael D.

doi:10.1002/mrc.1260301012

Cited by 10 publications

(4 citation statements)

References 14 publications

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“…An impressive number of marine invertebrates have been found to have promising cytotoxic activity against a variety of cancer cell lines. One such invertebrate, the gorgonian octocoral Briareum asbestinum Pallas, has been the subject of intense investigation in our laboratory (1)(2)(3). The secondary compounds of B. asbestinum are unusually diverse and consist mainly of briarane and asbestinane class diterpenoids (4).…”

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“…Although produced by a different terpene cyclization pathway, both classes consist of bicyclic molecules with fused sixand ten-membered rings. We have recently reported the isolation and structures of nine tetracyclic diterpenes, 4-deoxyasbestinins A-D (1,2), and asbestinins 6-10 (3), from this gorgonian. These diterpenes were found to be active against several human tumor cell lines at a 1-10 µ level.…”

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Isolation and Structures of Sixteen New Asbestinin Diterpenes from the Caribbean Gorgonian Briareum asbestinum

Rodrı́guez

Cóbar²,

Martínez³

1994

J. Nat. Prod.

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Sixteen new diterpenoids, representative of the asbestinane skeletal class, have been isolated from shallow water colonies of the Caribbean gorgonian octocoral Briareum asbestinum. The structures of these secondary metabolites, named asbestinin-11 [1], asbestinin-12 [3], asbestinin-13 [4], asbestinin-14 [5], asbestinin-15 [7], asbestinin-16 [8], asbestinin-17 [9], asbestinin-18 [10], asbestinin-19 [11], asbestinin-20 [12], asbestinin-21 [13], asbestinin-22 [14], asbestinin-23 [15], 11-acetoxy-4-deoxyasbestinin E [16], 11-acetoxy-4-deoxyasbestinin F [17] and 4-deoxyasbestinin G [18], were defined by chemical and spectroscopic methods. These specimens of B. asbestinum, collected in Puerto Rico, yielded almost exclusively diterpenoids possessing the asbestinane carbon skeleton thus suggesting minor biosynthetic variations for this gorgonian. In this paper, we also revise the structures of the known asbestinin-6 and asbestinin-7 to asbestinanes 2 and 6, respectively.

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Isolation and Structures of Sixteen New Asbestinin Diterpenes from the Caribbean Gorgonian Briareum asbestinum

Rodrı́guez

Cóbar²,

Martínez³

1994

J. Nat. Prod.

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“…The relative configurations of C-20, C-23, and C-24 were determined based on J-based configuration analysis [11]. In addition to the 3 J H,H values, 2,3 J C,H values were detected using hetero half-filtered TOCSY (HETLOC) [12,13], phase-sensitive COSY (PS-COSY) [14], and phase-sensitive HMBC (PS-HMBC) [15,16] spectra of 1 in CD 3 OD. The relative magnitudes of coupling constants assigned from the 3 J H,H and 2,3 J C,H values indicated that each of C-17-C-20, C-20-C-22, C-22-C-23, and C-23-C-24 bonds adopted a single dominant con-former (Figure 4), which was further supported by the ROESY correlations (Figure 3).…”

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confidence: 99%

The Triterpenoids from Munronia pinnata and Their Anti-Proliferative Effects

Yang,

Liu,

Wei

et al. 2023

Molecules

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Six new tirucallane-type triterpenoids, named munropenes A–F (1–6), were extracted from the whole plants of Munronia pinnata using a water extraction method. Their chemical structures were determined based on detailed spectroscopic data. The relative configurations of the acyclic structures at C-17 of munropenes A–F (1–6) were established using carbon–proton spin-coupling constants (2,3JC,H) and inter-proton spin-coupling constants (3JH,H). Furthermore, the absolute configurations of munropenes A–F (1–6) were determined through high-performance liquid chromatography (HPLC), single-crystal X-ray diffraction, and electronic circular dichroism (ECD) analyses. The antiproliferative effects of munropenes A–F were evaluated in five tumor cell lines: HCT116, A549, HepG2, MCF7, and MDAMB. Munropenes A, B, D, and F (1, 2, 4, and 6) inhibited proliferation in the HCT116 cell line with IC50 values of 40.90, 19.13, 17.66, and 32.62 µM, respectively.

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“…Specifically, a correlation between the acetate methyl group and the C19 methyl group as well as the correlation between the acetate methyl with the C1 methine provide important insights. The original structural assignment was based on the assumption that the cyclohexane ring of C2−C11 cyclized cembranoids must be locked into a boat conformation. , However, if true, then the observed acetate methyl NOEs are inconsistent with an α C11 flagpole acetate. More consistent with the observed NOESY data is a chair cyclohexane in which the C11 acetate resides on the β face and the C20 methyl is equatorial.…”

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Total Synthesis of the Proposed Structure of Briarellin J

Crimmins

Rodrı́guez

2010

Org. Lett.

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The total synthesis of the originally proposed structure of briarellin J is reported in 15 steps from a known compound and in 23 steps from readily available materials. Key reactions include an exo selective intramolecular Diels-Alder and a substrate controlled hydroboration. Discrepancies in the spectroscopic data of the synthetic and natural material led to a revision of the assigned structure.The eunicellins, briarellins, asbestinins, and sarcodyctins are related subclasses of the C2-C11 cyclized cembranoid diterpenes isolated as secondary metabolites of alcyonarians (octocoral) found in the Caribbean and Pacific Ocean. 1 Intense synthetic efforts over the past decade have resulted in numerous total syntheses of members of the various subclasses. 2 While the natural role of these diterpenes is proposed to involve predation deterrence, 3 the briarellin diterpenes also exhibit activity against the malaria parasite Plasmodium falciparum. 4 The presence of all four subclasses in the same organism provides evidence for the biosynthetic proposal advanced by Faulkner in which a cembrane skeleton serves as the precursor to each subclass. 5 Notably, a suprafacial 1,2-methyl shift from C11 to C12 would be required to transform the briarellins into the asbestinins (Figure 1). Briarellin J, like almost all briarellins, 6 was isolated by Rodríguez and co-workers from the gorgonian octocoral Briareum polyanthes. 4 The carbon framework and relative stereochemistry of briarellin J was assigned on the basis of NMR studies and comparison of the NOESY spectrum to that of the previously isolated and assigned briarellin D. Interestingly, briarellins A-D 7 and J-P 4 have been assigned C11 configurations opposite to those assigned for briarellins E-I 8 (Figure 2). The assigned C11 configuration for briarellins A-D and J-P was based on the absence of an NOE correlation between the C11 methyl and the α C14 methine, whereas this correlation is clearly present in briarellins E-I. The proposed β C11 methyl in briarellins A-D and J-P conflicts with Faulkner's biosynthetic proposal since a very unlikely 1,2-antarafacial methyl shift would be required to generate an asbestinin ( Figure 1). 1b Although the relative and absolute stereochemistry of briarellins E and F have been established via total synthesis 9 by the Overman group, no synthetic efforts towards briarellin A-D or J-P have been reported to date.We previously reported the enantioselective preparation of medium ring ethers 10 via a glycolate aldol/ring-closing metathesis strategy and have applied this method to the synthesis of members of the eunicellin 11 and asbestinin classes. 12 Due to the interesting inconsistency with Faulkner's proposed biosynthesis and our experience in the synthesis of C2-C11 cyclized cembranoid diterpenes, we chose briarellin J as a prime target for total synthesis. Retrosynthetically (Scheme 1), the proposed structure of briarellin J (1) was envisioned to arise from a late stage substrate controlled hydroboration of hexahydroisobenzofuran 2 to ...

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Two‐dimensional NMR spectra of asbestinin diterpenes isolated from Briareum asbestinum (Pallas). Total stereochemical assignment by two‐dimensional NMR techniques

Cited by 10 publications

References 14 publications

Isolation and Structures of Sixteen New Asbestinin Diterpenes from the Caribbean Gorgonian Briareum asbestinum

Isolation and Structures of Sixteen New Asbestinin Diterpenes from the Caribbean Gorgonian Briareum asbestinum

The Triterpenoids from Munronia pinnata and Their Anti-Proliferative Effects

Total Synthesis of the Proposed Structure of Briarellin J

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