Marine sesquiterpenes

Euplotin C Sesquiterpene Marine ciliate Euplotes crassus Analytical NPC UV 215 nm, ESI-MS 98... 

Intramolecular Friedel-Crafts acylations of olefins also give cycHc a,P-unsaturated cycHc ketones. Cyclopropane fused bicyclo[5.3.0]octenones, thus obtained, were used in the preparation of the marine sesquiterpenes, africanol [53823-07-7] and dactjlol [58542-75-9] (174). 

Cyclobuta[fc]chroman-4-ols, derived from chromones by a [2+2] photocycloaddition to ethylene, are prone to acid-catalysed rearrangements. Elaboration of the parent system prior to rearrangement has enabled the marine sesquiterpene filiformin <96JOC4391>, the henzo-1,3-dioxan nucleus of averufin <96JOC9164> and cyclobuta[h][l]benzoxepin-8,9-diones <96CC1965> to be synthesised. 

Naturally occurring marine isonitriles are either sesquiterpenes or diterpenes with one, two, or three isocyano (or isocyano-related) functions. As mentioned previously, it usually is the same carbon that bears the -NC, -NCS, or -NHCHO function. Commonly encountered in sesqui- and diterpenes are... 

The majority of marine isonitriles are sesquiterpenes with the molecular formula, C16H25N. Often cyclic, these are alkanes or alkenes possessing only a single isocyano-related functional group. In the mass spectrum, they exhibit a molecular ion at w/z 231, or an intense fragment ion at m/z 204, indicative of M+-HCN. Some are crystalline (see Table 2). With few exceptions most of the isothiocyano and formamido analogs are minor noncrystalline metabolites (see Table 3). 

Sims JJ, Fenical W, Wing RM, Radlick P (1971) Marine natural products. I. Pacifenol, arare sesquiterpene containing bromine and chlorine from the red alga, Laurenciapacifica. J Am Chem Soc 93 3774-3775... 

Sims JJ, Lin GHY, Wing RM (1974) Marine natural products. X. Elatol, a halogenated sesquiterpene alcohol from the red alga Laurencia elata. Tetrahedron Lett 39 3487-3490 Singh S, Kate BN, Banerjee UC (2005) Bioactive compounds from cyanobacteria and microalgae an overview. Crit Rev Biotechnol 25 73-95... 

Angerhofer CK, Pezzuto JM, Koenig GM, Wright AD, Sticher O. (1992) Antimalarial activity of sesquiterpenes from the marine sponge Acanthella klethra. J Nat Prod 55 1787-1789. 

Laronze and colleagues used a similar procedure to built the dihydrofuran ring of the marine sesquiterpene Aplysin (123). 

Oppolzer and Battig have prepared the marine sesquiterpene via ingenious application of iterative intramolecular magnesium-ene reactions . Aldehyde 672 was converted to the allylic chloride 673, the Grignard of which was heated at 60 °C for 23 hours and subsequently treated with acrolein to furnish alcohol 674 (Scheme LXX). An analogous sequence transformed 675 to 676 and set the stage for final transformations which were patterned after earlier work. 

More recently, the sesquiterpene A -isonakafuran-9-hydroperoxide (76) (P2j, O— O = 1.458 A, H—O—O—C = 63.3°, Figure 30) has been isolated from the dichlorometh-ane/methanol extract of the marine sponge Dysidea sp. nov . The peroxide is inhibitory to the marine fungus Trichophyton mentagrophytes and to murine leukemia cells. In view... 

The isoprenoids contribute most to the list of structural similarities in the sea and on land. They range from common classes in both ecosystems, such as drimane sesquiterpenes, to rare classes in the sea, such as the trichothecenes (Chart 8.3.11). The similarity in marine and terrestrial polyether triterpenes (Chart 8.3.12) may be seen as convergence toward chemically favored structures, starting from squalene as a biosynthetic precursor. Similar conclusions may apply to polycyclic triterpenes. 

Killday, K.B. Longley, R. McCarthy, P.J. Pomponi,S.A. Wright, A.E. Neale, R.F. Sills, M.A. (1993) Sesquiterpene-derived metabolites from the deep water marine sponge Poecillastra sollasi. J. Nat. Prod., 56, 500-7. 

Wright, A.E. Pomponi, S.A. McConnell, O.J. Kohmoto, S. McCarthy, P.J. (1987) (+)-Curcuphenol and (+)-curcudiol, sesquiterpene phenols from shallow and deep wata collections of the marine sponge Didiscus Jlavus. J. Nat. Prod., 50, 976-8. 

The first sesquiterpene thiocyanate to be isolated from a marine sponge was (15, 45, 65, 7/ )-4-thiocyanato-9-cadinene (253) from Trachyopsis aplysinoides. The structures of this compound and of an isothiocyanate with a new carbon skeleton (254), were determined by X-ray analysis and two additional isothiocyanates (255-256) were identified [258]. Isothiocyanate 254 was synthesised using an oxidative radical cyclisation reaction as a key step [259]. 

The diverse, widespread and exceedingly numerous class of natural products that are derived from a common biosynthetic pathway based on mevalonate as parent, are synonymously named terpenoids, terpenes or isoprenoids, with the important subgroup of steroids, sometimes singled out as a class in its own right. Monoterpenes, sesquiterpenes, diterpenes and triterpenes are ubiquitous in terrestrial organisms and play an essential role in life, as we know it. Although the study of terrestrial terpenes dates back to the last century, marine terpenes were not discovered until 1955. 

Marine organisms have also been intensively examined for their sesquiterpene content. Dysidea herbacea is a sponge species which has yielded new metabolites for more than 20 years, and no doubt further collections from different locations will continue to reveal new chemistry. 

From the marine sponge Haliclona sp. (also known as Adocia sp.), a family of hexaprenoid hydroquinones called adociasulfates, have been recently reported as inhibitors of kinesin motors [100,101], These types of compounds were also found in several soft corals, such as Lemnalia africana [102], Okinawan soft coral of Nephthea sp. [103], and the gorgonian Alertogorgia sp., which yielded the cytotoxic tricyclic sesquiterpene, suberosenone [104],... 

The marine isothiocyanates, with more than 80 compounds isolated so far, form the largest group of naturally occurring isothiocyanates. This well-established group of marine natural products is constituted mainly by terpene metabolites present as sesquiterpene and diterpene derivatives. The non-terpene isothiocyanate compounds include two cylindricine alkaloids and a series of long-chain aliphatic metabolites. Marine sponges constitute the main source of these compounds, although they are also found in nudibranches and tunicates. 

Although marine organisms produce a large number of isocyanates, isothiocyanates, and formamides, the corresponding thiocyanates have rarely been encountered. Indeed, the thiocyanate functionality has only been found in six sesquiterpenes (263-268), in four tricyclic quinoline alkaloids (271-274), and in psamaplin B (172) (included in the bromotyrosine derivatives discussed in the disulfide/polysulfide section). They have been found in marine sponges, as well as in nudibranches and tunicates. 

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