Sesquiterpenoid epoxides

Two groups of hormones regulate development and reproduction in insects, namely the ecdysteroids and the JHs. In crustaceans too, ecdysteroids are involved in the hormonal control of growth, and a chemical compound, which is similar to the JHs of insects, is present and thought to play a role in crustacean reproduction and development. The insect JH is a species-specific acyclic sesquiterpenoid epoxide, which is synthesized in a pair of retrocerebral epithelial organs called the corpora allata (CA see Fig. 1). In decapod crustaceans, MF is the unepoxidated form of the insect JH III and it is synthesized and secreted from the MOs (see Section 3.2.4). 

Sesquiterpenoid. 203, 1071 Sex hormone, 1082-1083 Sharpless, K. Barry. 734 Sharpless epoxidation, 735 Shell (electron), 5 capacity of, 5 Shielding (NMR). 442 Si prochirality, 315-316 Sialic acid. 997 Side chain (amino acid), 1020 Sigma (cr) bond, 11 symmetry of, 11 Sigmatropic rearrangement, 1191-1195... 

The first enantioselective total synthesis of the sesquiterpenoid heliannuol D 56 has been reported by Shishido and co-workers. The key step was a base-mediated (NaOH) intramolecular cyclisation of the phenolic epoxide mixture 55 (R1 = MOM, R2 = H and R1 = H, R2 = MOM). Heliannuol D (and the eight-membered congener, heliannuol A) is an allelopathic agent isolated from cultivated sunflowers (Helianthus annuus L.SH-222) <00JCS(P 1)1807>. 

G.l.c. papers of interest include the classification of 22 acyclic monoterpenoid alcohols according to retention indexes, resolution of cyclic ketones [e.g. ( )-menthone, ( )-isomenthone] as diethyl (+)-tartrate acetals, and the use of lanthanide shift reagents to resolve non-terpenoid racemic epoxides.The occurrence and prevention of monoterpenoid hydrocarbon isomerization during silica gel chromatography has been examined and the separation of monoterpenoids and sesquiterpenoids by gel permeation chromatography is reported. Monoterpenoid hydrocarbons have been selectively extracted from essential oils using dimethylsilicone. ... 

The final steps in a recent synthesis of the sesquiterpenoid mycotoxin verrucarol (6) required selective epoxidation of a 2,2-disubstituted double bond in the presence of a IriNuhstiiutcd one. This reaction was effected, in 85% yield, by treatment of 4 with t-Inilyl hydroperoxide and Mo(CO)6. Use of VO(acac), as catalyst resulted in some decomposition in addition to the desired epoxidation. The final step was deprotection ol 8 with lluoridc ion to give 6.2... 

Interest continues in the isolation and structural elucidation of halogenated sesquiterpenoids produced by marine organisms (e.g. algae). Many of these compounds are chamigrane derivatives and new members of this group include prepacifenol epoxide (89)46 from Aplysia californica, elatol (90)47 from Laurencia elata, nidifidienol (91)48 from Laurencia nidifica, and the compounds (92) and (93)49 from... 

The structure of chlorosantonin (491) obtained from santonin 4,5-epoxide with hydrogen chloride gas has been solved by X-ray analysis. Undoubtedly the most remarkable sesquiterpenoid rearrangement is that observed when the dried sodio salt of (492) is heated to reflux in excess phosphorus oxychloride. The rearrangement product in question was isolated by removal of the excess POCI3, followed by neutralization with concentrated aqueous ammonia. The resultant ether extract was treated with hot 15% sodium hydroxide and the product mixture was distilled and purified by column chromatography. One of the products (about 3% yield) has been identified by X-ray analysis as (493), but as yet no mechanism has been suggested... 

Further work on the conformation of certain germacrane sesquiterpenoids has been performed using both X-ray analyses and the intramolecular nuclear Overhauser effect (n.o.e.). Complete details of the X-ray analysis of the silver nitrate adduct of germacratriene have been published. In addition to demonstrating its conformation as (222), this analysis correlates the known reactivity (to epoxidation) of the three double bonds (4=5 > 1=10 > 7=11) with their torsional strains. The X-ray analysis of a heavy-atom derivative of pyrethrosin (223) has revealed that some stereochemical adjustments are required with respect... 

In their synthesis of fukinone, Marshall and Cohen converted the known ene-ol (340) into (341) by acetylation, allylic oxidation, and conjugate methylation with dimethylcopperlithium. A Wolff-Kishner reduction of (341) followed by oxidation of the resultant alcohol and enol-acetylation yielded (342). The epoxide of (342) was thermolysed to give (343) which, on reaction with iso-propenyl-lithium and selective oxidation, gave the ketol (344) which was converted in two steps into fukinone (335). A number of sesquiterpenoids, e.g. fukinanolide (345), with the rearranged eremophilane skeleton viz. fukinane (346 R = Me) are known. Nay a and Kobayashi have now prepared this parent hydrocarbon by Raney nickel reduction of the thioacetal of fukinan-8-al (346 R = CHO). 

A rather different approach to the hydroazulenic synthesis has been adopted by Hendrickson and Boeckman. Treatment of 1-cyclopentenylcarboxalde-hyde (411) with the pyrrolidine enamine of cyclopentanone (412) yielded the thermodynamically most stable adduct (413) which, on quaternization and base-induced fragmentation, gave the acid (414) in 25% yield. Furthermore, the acid (414) has been converted into the epoxide (415) and the (5-lactone (416), both of which are potential synthetic precursors of guaiane-type sesquiterpenoids, e.g. pseudoguaianolides. 

Trichothecene mycotoxins are a group of sesquiterpenoid mycotoxins produced by fungi from the Fusarium family. There are four types Type-B such as nivalenol differs from Type-A such as diacetoxyscirpenol by the presence of the keto-group in the C8 position. Type-C has an additional epoxide group, and Type-D are macrocyclic trichothecenes. Human and animal toxicoses by these toxins have been dne to the consnmption of contaminated grain. The structure of some of the Type-A and Type-B componnds is shown in Table 14.2. 

New bisabolane sesquiterpenoids from a variety of plant sources include (95)— (102).59-64 f-y-Bisabolene-8,9-epoxide (103) has been isolated from the alga Laurencia nipponica.65 This compound is possibly the precursor of various halo-genated chamigranes which are abundant in Laurencia algae. 

Eudesmanolides (such as (3)) constitute a large family of natural sesquiterpenoids, with more than 500 members described to date.tl] Their pharmacological properties include antifungal, anti-inflammatory, and antitumor activities among others,[2] but many of them are scarce in nature. To facilitate their chemical synthesis, a novel procedure has recently been developed that provides satisfactory overall yields.[3] Our method is based on the titanocene-catalyzed cyclization of epoxygermacrolides (such as (2)) easily prepared by selective epoxidation of accessible germacrolides such as ( I )-l 1 (5,13-dihydrocostunolidc (1)[4]. 

A bicyclogermacrane type sesquiterpenoid with a C-14 carboxylic acid, madolin P (290) was isolated from stems and roots of A. kaempferi [244]. It is very similar to madolin B (299) but having a C-l/10 double bond instead of an epoxide. 

The aerial parts of T. densum ssp. sivasicum yielded the known sesquiterpenoids, 8a-hydroxyanhydroverlotorin (119), deacetyltulipi-nolide-lp,10a-epoxide (116), spiciformin (97), deacetyllaurenobiolide (81), isospiciformin (98), la-hydroperoxy-l-desoxo-chrysanolide (55),... 

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