Marine sesquiterpene

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. 

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. 

Ritter reaction of the triene 287 in triflic acid, performed to accomplish the synthesis of a marine sesquiterpene, gave the product acetamide derivative via a predominant trans antiparallel addition of H+ and acetonitrile to the endocyclic double bond920 [Eq. (5.343)]. 

The diversity of ring systems found in Laurencia is shown in Scheme 3.2 (553), although the present organization of marine sesquiterpenes does not follow these categories, but rather continues the previous one (1). 

The photo-cycloaddition of ethylene to 3-alkoxy chromones such as 315 has been applied to the synthesis of marine sesquiterpene filiformin and congeners (Scheme 43) <1996JOC4391>. Tandem [2+2] 7i-photo-cycloaddi-tion and y-hydrogen abstraction provided tetracyclic intermediate 316 which was converted to terpene 317 by subsequent oxetane ring reduction and acid-catalyzed rearrangement. 

The marine sesquiterpene nakijiquinones were synthesized and biologically evaluated by H. Waldmann et al. The core structure of the natural product was assembled via a reductive aikyiation of a bicyclic enone with tetramethoxybenzyl iodide. This aryl iodide was obtained in a two-step procedure treatment of the corresponding 1,2,4,5-tetramethoxybenzene with HBr/paraformaldehyde/AcOH followed by the Finkeistein reaction to replace the bromide with iodide. 

In the laboratory of T.-L. Ho, the total synthesis of the novel marine sesquiterpene (+)-isocyanoallopupukeanane was completed." In the endgame of the synthesis, it was necessary to install the isocyano group onto the tricyclic trisubstituted alkene substrate so that it will occupy the more substituted carbon atom (according to Markovnikov s rule). The Ritter reaction was chosen to form the required carbon-nitrogen bond. The alkene substrate was dissolved in glacial acetic acid and first excess sodium cyanide followed by concentrated sulfuric acid was added at 0 °C. The reaction mixture was stirred at ambient temperature for one day and then was subjected to aqueous work-up. The product A/-alkyl formamide was subsequently dehydrated with tosyl chloride in pyridine to give rise to the desired tertiary isocyanide which indeed was identical with the natural product. 

The capnellene and hirsutene marine sesquiterpenes are ideal candidates for radical cyclizations and both have been elaborated via carbonyl-alkyne cyclizations (equations 141-143). Thus treatment of the ketone (117) with the sodium naphthalene radical anion gives the triquinane (118). Subsequent allylic... 

Ilimaquinone (29) is a marine sesquiterpene quinone first isolated in 1979 from the sponge Hippospongia metachromia90 It has been reported to have mild antibacterial, antiviral, antifungal, and anti-inflammatory activities, but more interestingly, ilimaquinone has been found to break down the Golgi apparatus into small vesicles, thereby blocking cellular secretion.91 92... 

Intramolecular Friedel-Crafts acylation provides a useful synthetic approach to cyclic ketones. The cyclization is well-suited to the preparation of six- and particularly five-membered rings, as used in key steps in routes to methyl dihydrojasmonate (equation 3), and precursors to some marine sesquiterpenes (equation 4) and the theoretically interesting spiro[4.4]nonatetraene (equation 5). Extension to cyclo-heptanones has been achieved, - but tars were formed on attempting to prepare cyclooctanones. ... 

Table 1 provides an update of the Chang-Scheuer summary and lists the structures of all new marine sesquiterpene isocyanides and related compounds including isothiocyanates, (1 - 67), by compound class,... 

Every effort has been made to include all known naturally occurring marine sesquiterpene/quinones as of September 1992. While compounds 9 0 to 93 appear not to satisfy the criteria of the survey, they are in fact aromatic ring contracted analogues. Likewise, although compounds 97 to 108 have received recognition in the literature as polyketides, in the absence of any definitive biosynthetic evidence to the contrary it is the contention of this author that they be considered as... 

Careful examination of these stereochemical assignments revealed that in many instances a simple chemical transformation could have provided a more secure correlation. Over the last few years we have pursued several chemical correlations between marine sesquiterpene/quinones with interesting and useful consequences. Some of these results are highlighted below. 

More recently we completed a re-examination of the marine sesquiterpene/quinone spongiaquinone (33). This investigation was prompted by our discovery from a southern Australian marine sponge of the... 

Additional opportunities exist to chemically inter-relate naturally occurring marine sesquiterpene/quinones, and in doing so to both resolve their absolute stereostructures and to explore their chemical reactivity. 

The present volume reflects these developments, and there is a growing emphasis on bioactive natural products. Articles in this volume include those on structure-activity relationships of highly sweet natural products, chemical constituents of cchinodenns, diterpenoids from Rabdosia and Eremophila sp., structural studies on saponins, marine sesquiterpene quinoncs and antimicrobial activity of amphibian venoms. The reviews on bioactive metabolites of Phomopsis, cardenolide detection by ELISA, xenocoumacins and bioactive dihydroisocoumarins, CD studies of carbohydrate-molybdate complexes, oncogene function inhibitors from microbial secondary metabolites and Gelsemium and Lupin alkaloids present frontier developments in several areas of natural product chemistry. It is hoped that the present volume, which contains articles by eminent authorities in each field, will be received with the same enthusiasm as the previous volumes of this series. 

Balme, G. and Bouyssi, D. (1991) Total synthesis of the triquinane marine sesquiterpene ( )A 02) capneUene using apaUadium-catalyzed bis-cyclization step. Tetrahedron, 50,403-14. 

Recently, the MacMillan group reported the organocatalytic three-step total synthesis of (+)-Frondosin B (131), a marine sesquiterpene isolated from the marine... 

In syntheses of two marine sesquiterpenes, africanol 172 and dactylol 173, Paquette [39] prepared the bicydic aUylic alcohol 175 in nine steps from 4,4-di-methyl cyclohexanone 174. The Claisen-Johnson rearrangement was highly stereoselective and gave rise to ester 176 with the proper configuration of the side chain methyl in relation to dactylol 173 (Scheme 6.26). 

El Sayed, K.A., M. Yousaf, M.T. Hamann, M.A. Avery, M. Kelly, and P. Wipf, 2002. Microbial and chemical transformation studies of the bioactive marine sesquiterpenes (5)-(-r) -curcuphenol and -curcudiol isolated from a deep reef collection of the Jamaican sponge Didiscus oxeata. LNoL t., 65 1547-1553. 

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