Diterpenes marine

Clare, A.S., Rittschof, D., Gerhart, D.J., Hooper, I.R., and Bonaventura, J., Antisettlement and narcotic action of analogues of diterpene marine natural product antifoulants from octocorals, Mar. Biotechnol., in press. 

Provided that the silanolate elimination proceeds with anti selectivity, it must be concluded, that the intermediate homoallylic alcohol has an anti configuration, and thus the reagent has an ( -configuration. Acidic hydrolysis of the enol ether leads to enones the overall sequence consists of a nucleophilic acroylation. This has also been applied in the total synthesis of the marine diterpene ( )-aplysin-2067. 

The first total synthesis of the marine dolabellane diterpene (+)-4,5-deoxy-neodolabelline (70) was accomplished by D. R. Williams et al. [58]. The trans-disubstituted dihydropyran moiety in key intermediate 69 was efficiently prepared from mixed acetal 66 by RCM with second-generation catalyst C and subsequent Lewis acid-catalyzed allylation of ethyl glycosides 67 with allylsi-lane 68 (Scheme 12) [59]. 

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... 

Frankincense, also called olibanum, is a natural oleo gum resin that exudes from incisions in the bark of Boswellia trees [46, 47]. Diterpenes like incensole or isoincensole and their oxide or acetate derivatives (see Figure 10.3) are characteristic biomarkers of olibanum [48]. Although diterpenoid hydrocarbons possessing the cembrane skeleton have been isolated from a variety of terrestrial and marine organisms, their occurrence and particularly that of cembrenes A and C (see Figure 10.3) is supplementary proof of the presence of olibanum in a sample. Optimisation of the SPME conditions was done with the aim of trapping these low volatile diterpenes. 

Danise B, Minale L, Riccio R, Amico V, Oriente G, Piattelli M, Tringali C, Fattorusso E, Magno S, Mayol L (1977) Further perhydroazulene diterpenes from marine organisms. Experientia 33 413 115... 

In the course of dolastane synthesis (the dolastanes are a group of marine diterpenes) interesting rearrangements catalyzed by Lewis acids were found. Treatment of the trienone 293 with excess (1.5 eq) ethylaluminum dichloride at low temperatures (—5°C, 48 h) gave the tetracyclic enone 295 in 53% yield while the tricyclic dienone 296 (50%) was formed at room temperature (equation 102)156. It was assumed that both products can be derived from the common zwitterion 294 which undergoes intramolecular alkylation at low temperatures (path a) whereas an alkyl shift takes place at elevated temperatures (path b), followed by a 1,2-hydride shift (equation 102). 

Phytene is an example of a diterpene. It is found as the phytyl side chain in chlorophyll a and vitamin K. Haslene is an example of a sesterpene. It is an imsaturated and branched simple lipid synthesized by marine pennate diatoms. One of the largest femilies of terpenes... 

Koenig GM, Wright AD, Angerhofer CK. (1996) Novel potent antimalarial diterpene isocyanates, isothiocyanates, and isonitrile from tropical marine sponge Cymbastela hooperi. J Org Chem 61 3259-3267. 

Abstract The isolation, structure and total synthesis of members of four classes of diterpenes has been summarized. Dolabellanes, neodolabellanes, dolastanes and neodolas-tanes are structurally related bi- or tricyclic diterpenes. Dolabellanes belong to a continuously growing class of diterpenes being isolated from marine and terrestrial sources. The published work on isolation and synthesis since 1998 has been summarized. Neodolabellanes represent a scarce class of diterpenes that have been isolated exclusively... 

About 25 diterpenes (107-130) of the dolastane-type featuring a hydroben-zo[/]azulene ring system have been isolated exclusively from marine sources (Fig. 14) [61-76]. 

Kohmoto, S. McConnell, O.J. Wright, A. Cross, S. (1987) Isospongiadiol, a cytotoxic and antiviral diterpene from a Caribbean deep water marine sponge, Spongia sp. Chem. Lett., 1687-90. 

Matthie. G.F. Konig, G.M. Wright, A.D. (1998) Three new diterpenes from the marine soft coral Lobophytum crassum. J. Nat. Prod., 61, 237-40. 

Vuong, D. Capon, R.J. (2000) Phorbasin A a novel skeleton diterpene from a southern Australian marine sponge, Phorbas species. J. Nat. Prod., 63, 1684-5. 

Research to date focused on isolating insecticidal prototype leads from marine origin has resulted in the report of about 40 active compounds.44 In an attempt to summarize these compounds and their activity margins, they have been categorized into seven classes of chemical structures polyhalogenated monoterpenes, polyhalogenated C15-metabolites, diterpenes, peptides and amino acids, phosphate esters, sulfur-containing derivatives, and macrolides. 

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. 

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. 

In contrast to the small number of known halogenated (chlorinated) terrestrial diterpenes (vide supra), the number of marine diterpenes is very large, and more than 130 were documented in the initial survey (7). 

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