Chamigrane metabolites from a Jamaican variety of laurencia obtusa

Brennan, Mary; Erickson, Karen L.; Minott, Donna A.; Pascoe, Keith O.

doi:10.1016/s0031-9422(00)82349-3

Cited by 35 publications

(43 citation statements)

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“…(1) those belonging to the α-chamigrene series possessing a trisubstituted double bond between C-7 and C-8 (1-26); (2) possessing an exomethylene group at C-7 (27-77); (3) those featuring an oxygenation site at C-7 (78-99); and (4) those with either a 5,10-epoxide ring system (100-117) or another epoxide (118)(119)(120)(121)(122)(123)(124) or a lactone ring connecting the two sixmembered rings (125)(126)(127)(128)(129). Most chamigranes possess various halogen and oxygen substitutions, with C-10 being a favored position for a Br substitution.…”

Section: Chamigranes and Related Sesquiterpenesmentioning

confidence: 99%

The Laurencia Paradox: An Endless Source of Chemodiversity

Harizani

Iοannou

Roussis

2016

Progress in the Chemistry of Organic Natural Products

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Nature, the most prolific source of biological and chemical diversity, has provided mankind with treatments for health problems since ancient times and continues to be the most promising reservoir of bioactive chemicals for the development of modern drugs. In addition to the terrestrial organisms that still remain a promising source of new bioactive metabolites, the marine environment, covering approximately 70% of the Earth's surface and containing a largely unexplored biodiversity, offers an enormous resource for the discovery of novel compounds. According to the MarinLit database, more than 27,000 metabolites from marine macro- and microorganisms have been isolated to date providing material and key structures for the development of new products in the pharmaceutical, food, cosmeceutical, chemical, and agrochemical sectors. Algae, which thrive in the euphotic zone, were among the first marine organisms that were investigated as sources of food, nutritional supplements, soil fertilizers, and bioactive metabolites.Red algae of the genus Laurencia are accepted unanimously as one of the richest sources of new secondary metabolites. Their cosmopolitan distribution, along with the chemical variation influenced to a significant degree by environmental and genetic factors, have resulted in an endless parade of metabolites, often featuring multiple halogenation sites.The present contribution, covering the literature until August 2015, offers a comprehensive view of the chemical wealth and the taxonomic problems currently impeding chemical and biological investigations of the genus Laurencia. Since mollusks feeding on Laurencia are, in many cases, bioaccumulating, and utilize algal metabolites as chemical weaponry against natural enemies, metabolites of postulated dietary origin of sea hares that feed on Laurencia species are also included in the present review. Altogether, 1047 secondary metabolites, often featuring new carbocyclic skeletons, have been included.The chapter addresses: (1) the "Laurencia complex", the botanical description and the growth and population dynamics of the genus, as well as its chemical diversity and ecological relations; (2) the secondary metabolites, which are organized according to their chemical structures and are classified into sesquiterpenes, diterpenes, triterpenes, acetogenins, indoles, aromatic compounds, steroids, and miscellaneous compounds, as well as their sources of isolation which are depicted in tabulated form, and (3) the biological activity organized according to the biological target and the ecological functions of Laurencia metabolites.

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Section: Chamigranes and Related Sesquiterpenesmentioning

confidence: 99%

The Laurencia Paradox: An Endless Source of Chemodiversity

Harizani

Iοannou

Roussis

2016

Progress in the Chemistry of Organic Natural Products

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“…as such or in a different conformation) are limited, to our knowledge, to enones (-)-6 [4] and (+)-8 [5]. 2.3.…”

Section: (+)-I7mentioning

confidence: 99%

“…-This work has shown that chair-chair inversion of ring B of CI -chamigranes to the so far rare inverted-chair conformation, such as in (-)-6 [4], can also occur in the absence of bonding interactions, contrary to previous views [lo]. The driving force to ring-B chair inversion lies mainly in repulsive interactions between Me-C(5) and an axial substituent at C(8), while in P-chamigrenes, repulsive interactions between CH,=C(5) and the axial substituents at C(8) and C(10) can be minimized in the ring-B 'normal'-chair conformation, at least in all cases studied so far [l].…”

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confidence: 95%

“…They are largely overlooked in the literature from the conformational viewpoint. The only exception is enone (-)-6, isolated from Laurencia obtusa collections of Jamaica [4], for which the inverted-chair conformation of ring B was proposed, based on its 'H-NMR coupling pattern (J(8,7) = 12.5 and 4.7 Hz) and on a chemical correlation with an 0-bridged chamigrane of established configuration; however, no dynamic phenomena were described [4].…”

mentioning

confidence: 99%

“…Another case is enone (-)-6 [4], where the additional driving force toward the ring-B inverted-chair conformation may be ascribed to the presence of the sterically demanding Me,,-C(9) in the 'normal'-chair conformation. The reason why, in contrast, (+)-8 has a ring-B 'normal'-chair conformation must be that an axial Br-atom at C(9) is less space demanding than a Me group.…”

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Conformational Studies of Marine Polyhalogenated α‐Chamigrenes Using Temperature‐dependent NMR spectra inverted‐chair and twist‐boat cyclohexane moieties in the presence of an axial halogen atom at C(8)

Guella

Chiasera

Pietra

1992

Helvetica Chimica Acta

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a-Chamigren-3-one (+)-8 bearing an axial C1-atom at C(8) exists as a largely dominant conformer with MeeC(5) at the envelope-shaped enone ring pointing away from CI,,-C(8) at the cyclohexane ring ( = B) in the 'normal' chair conformation, as shown by 'H-NMR. In contrast, the a -chamigren-3-ols (+)-9 and (+)-lo, obtained from hydride reduction of (+)-8, show a temperature-dependent equilibrium of conformers where the major conformers have ring B in the inverted-chair (and twist-boat for (+)-9) conformation to avoid repulsions between Me-C(5) and CI,,-C(8) (Scheme 1). This is in agreement with the conformation of the epoxidation product (+)-12 of (+)-9 where Me-C(5) is pushed away from CI,,-C(8) in a ring-B chair similar to that of (+)-8 (Scheme 2). Introduction of a pseudoequatorial Br-atom at C(2) of (+)-8, as in enone (+)-15 (Scheme 3 ) , does not affect the conformation; but a pseudoaxial Br-C(2) experiences repulsive interactions with H,,-C(7), as shown by the 'H-NMR data of the isomeric enone (+)-16 where the 'normal'-chair conformer Ca-16 is in an equilibrium with the inverted chair conformer ICP-16 (Scheme 3 ) . These results and the accompanying paper allow a unifying view on the conformational behavior of marine polybalogenated a -chamigrenes. This view is supported by the acid-induced isomerization of c( -chamigrene (+)-9 (inverted chair) to 8-chamigrene (+)-17 ('normal' chair; Scheme 4 ) , the driving force being the lesser space requirement of CH2=C(5) than of Me-C(5). This explains why P-chamigrenes are so common in nature.

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The IntramolecularMichael Reaction

et al. 1995

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Like its intermolecular counterpart, the intramolecular Michael reaction involves the addition of a nucleophile, often referred to as the donor, to an acceptor, usually an olefin bearing one or more functional groups capable of stabilizing a carbanion. Strictly speaking, the term Michael reaction refers to the 1,4‐, or conjugate, addition of a carbanion to an acceptor under basic conditions. However, just as the scope of a previous review dealing with the Michael reaction was expanded to encompass a wide range of acceptors and noncarbon‐centered donors, so too has the scope of this chapter. Furthermore, reactions occurring under both basic and acidic conditions are discussed. As suggested by the name, the intramolecular Michael reaction most often leads to the formation of a ring, either carbo‐ or heterocyclic. However, there are many examples of sequential, or tandem, Michael reactions wherein the first inter‐ or intramolecular Michael reaction is followed directly by an intramolecular variant leading to the formation of more than one ring. In other instances, a nucleophile is delivered to the β‐carbon atom of an acceptor in a process which does not lead to the production of a ring. These transformations are referred to as heteroconjugate addition reactions. In contrast to the intermolecular counterpart, the intramolecular Michael reaction has been formally reviewed only once. Two contemporary publications, however, have focused on the reaction and serve to highlight recent developments. The first example dates back to 1898 when Guthzeit reported that on standing at room temperature for a year, or upon treatment with a “small amount” of pyridine, ethyl α‐carboxyglutaconate transforms to the “bimeric” ester. Subsequent reinvestigation by Ingold and co‐workers led to the revised structure and to the suggestion that it arose via an initial inter‐ followed by an intramolecular Michael reaction. The first systematic study of the intramolecular Michael reaction appeared in 1945. Thus, treatment of a variety of substituted ethyl coumarinates with sodium alkoxide in alcohol solvent leads to coumarins. Of particular interest is the fact that the reaction proceeds efficiently even when the β carbon of the acceptor is substituted with two sterically demanding groups. This apparent lack of retardation by double substitution at the β carbon contrasts sharply with the intermolecular Michael reaction and appears to be general. Another example highlighting the susceptibility of sterically hindered systems to participate in intra‐ but not intermolecular Michael reactions comes from studies concerning the mode of activation of the antibiotics calicheamicin and esperamicin. Access to the tetracyclic precursor of a taxol analog was achieved via an intramolecular Michael addition to the relatively hindered β carbon of enone. The intramolecular Michael reaction again formed the subject of publications appearing in 1951, 1957, and 1962. During the 1960s, comparatively little study or use of the reaction was reported. A notable and historically significant exception, however, was Corey's use of it in a total synthesis of longifolene. This approach to the construction of tricyclic systems is similar to that suggested mechanistically in the base‐induced conversion of santonin to santonic acid. The 1970s and 1980s witnessed a dramatic increase in uses of the intramolecular Michael reaction. Much of the chemistry discussed in this chapter focuses upon material discovered during this time period.

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Chamigrane metabolites from a Jamaican variety of laurencia obtusa

Cited by 35 publications

References 15 publications

The Laurencia Paradox: An Endless Source of Chemodiversity

The Laurencia Paradox: An Endless Source of Chemodiversity

Conformational Studies of Marine Polyhalogenated α‐Chamigrenes Using Temperature‐dependent NMR spectra inverted‐chair and twist‐boat cyclohexane moieties in the presence of an axial halogen atom at C(8)

The IntramolecularMichael Reaction

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