Triterpenes tetracyclic

Takano et al. 69) exploited the asymmetric aldolization for the synthesis of more functionalized chiral products which possess units suitable for the construction of certain tetracyclic triterpenes, such as gibberellins and kaurenes. They described the enantioselective synthesis of the tricyclic enone (33) from the symmetric triketone (32) and its conversion into the gibbane framework. Again, (S)-proline was used as the catalyst. 

While squalene, the parent of all triterpenoids, is a linear acyclic compound, the majority of triterpeneoids exist in cyclic forms, penta- and tetracyclic triterpenes being the major types. Within these cyclic triterpenoids distinct structural variations lead to several structural classes of triterpenoids. Some of the major structures types of triterpenoids are shown helow. 

Van Tamelen has examined extensively the cyclization of monoepoxide-polyolefins (94). For example, he found (95) that the treatment of racemic epoxide 247 with SnCl in nitromethane provided a major product (35% yield) which was identified as the racemic tetracycle 248. This represents an over all, close simulation of the squalene tetracyclic triterpene bioconversion (except for optical activity). 

Bryodulcoside (= Bryodulcosigenin glycoside) (oxygenated tetracyclic triterpene cucurbitacin glycoside) Bryonia dioica (Cucurbitaceae) [root] Sweet... 

Although previous workers have suggested bacterial synthesis as a possible source of biogenic PAHs in modem sediments, Hase and Hites (1976) have shown that bacteria more likely only bioaccumulate them from the growth medium. Anaerobic aromatization of tetracyclic triterpenes appeared to have been demonstrated by Lohmann et aL (1990) by incubating radiolabeled j8-amyrin. 

The silver nitrate-impregnated silica gel G was used to obtain a separation with a group of tetracyclic triterpene alcohols, which could not be separated on untreated silica gel. However, on silica gel G (Ag impregnated), the Rf values were sufficiently different so as to enable the substances to be identified separately. Chloroform was used as the mobile phase. The tetracychc triterpenes were detected by spraying with one of the three reagents 50% sulfuric acid in water or 10% phosphomohbdic acid in ethanol or chlorosulfonic and acetic acids (1 2) followed by heating in an oven at 150°C. ... 

Various attempts to oxidize 7,8- and 8,9-unsaturated tetracyclic triterpenes such as (1) to the corresponding epoxides by reaction with perbenzoic acid afforded mixtures of epoxide with the 7,9(1 l)-diene. Fried et al. found that the difficulty is eliminated by use of m-chloroperbenzoic acid in chloroform, which gave exclusively... 

P. anthracophilus found on a Eucalyptus species were established at the same time. The work on eburicoic acid was carried out by Robertson in Liverpool. The elucidation of the structure of polyporenic acid A (5.161) benefited from experience gained in studies on the structure of lanosterol and on the penta-cyclic triterpenes. The identification of some structural features also showed the developing role of UV and IR spectroscopic methods in the 1950s. However, the purification of these compounds was impeded by the difficulty of separating the 8(9)-enes from the 7(8),9(ll)-dienes that often accompanied them. Initial studies on polyporenic acid A revealed the presence of a carboxylic acid, two hydroxyl groups and two double bonds, each of differing reactivity. One double bond was a terminal methylene since formaldehyde was obtained on ozonolysis whilst the other was more hindered. Typical of the tetracyclic triterpenes. 

One step in the production of (5), a key intermediate in a synthesis of the tetracyclic triterpene a-onocerin, involved allylic oxidation of the a,)3-unsaturated ester (1). This was accomplished with Se02 in boiling acetic acid.18b The unsaturated hydroxy lactone produced (2) was next to be converted into the saturated keto acid (5), presumably by a stepwise process. However, the Israeli investigators were pleas-... 

Helvolic acid (164) originally isolated from Aspergillus fumigatus has also been identified in Gliocladium species where it cooccurs with the 1, 2-dihydro analogue [59]. Helvolic acid shares the unusual tetracyclic triterpene skeleton of the fusidanes with fusidic acid and the cephalosporin Pi and all show antibacterial activity [230, 231]. 

Bryoniae radix Bryony root Bryonia alba L. and B. cretica ssp. dioica PLANCH. Cucurbitaceae, MD Tetracyclic triterpenes cucurbitadn gliicosides 1,L,E and dihydro-cucurbitacins E,B and aglycones Bryonia alba and B. dioica qualitatively similar contents of cucurbitacins Fig. 11,12... 

Colocyiithidis fructus Citrullus colocynthis (L.) SCHRAD, Ciicurbitaceae Tetracyclic triterpenes Cucurbitacin gliicosides E,i,L... 

Graliolae herba Giatiola officinalis L, Scropliulariaceae Tetracyclic triterpenes Cucurbitacin glucosides E,1,L and aglycones... 

Ecballii fructus Ecballium elaterium (L.) A.RICH. Cucurbitaceae Tetracyclic triterpenes Cucurbitacin glucosides and aglycones... 

Tetracyclic triterpene glycosides actein (acetyl-acteol xyloside), cimicifugoside (cimidgenol xyloside)... 

Biogenetically quassinoids can be regarded as degraded triterpenoids and are almost certainly derived from tetracyclic triterpenes. The conversion of the tetracyclic triterpene into quassinoid has been experimentally verified by using labeled mevalonate precursors [3-5] and follows the route originally proposed by Arigoni et ah [6] but extended by further degradation to quassinoids as shown in Scheme 1. 

The lanostanes are the most relevant group of the tetracyclic triterpenes (Tables 12-13). Many of this type of compounds are described as antiinflammatories and their mechanism of action has been studied frequently. Cycloartenol and some 3,4-seco-lanostane derivatives have been reported to have activity also. 

As is the case with other tetracyclic triterpenes, cucurbitacins are formed upon cyclization of the 35 isomer of 2,3-epoxy-2,3-dihydrosquaIene. This initial cyclization is followed by a more extensive rearrangement to give, among other compounds, cucurbitacins, as shown in Fig. (3) [37-39],... 

These four plants are endemic to the Mediterranean Area but have been introduced to other parts of Europe the bitter apple is also found in the savannahs of Africa. All parts of the plants are poisonous, especially roots and fruits. The compounds responsible are the cucurbitacines, a rather big family of tetracyclic triterpenes, occurring either in free form or as glycosides. They have been studied intensively (2, 43, 44, 45, 46). 

Ehrhardt, J.D., L. Hirth, and G. Ourisson Etude des tri-terpenes tetracycliques des feuiUes de tabac. Presence de cycloartenol absence de lanosterol [Study of the tetracyclic triterpenes in tobacco leaf. Presence of cycloartenol absence of lanosterol] Compt. Rendu Acad. Sci. 260 (1965) 5931-5934. 

As part of an investigation into the synthesis of tetracyclic triterpenes of the lanostane (27)-cycloartane (28) group, Packer and Whitehurst described the synthesis of the indan-2-one 29. Compound 29 has potential as a key intermediate in the synthesis of tetracyclic triterpenes, possessing the trans-CD ring junction and a carbonyl suitably positioned for introduction of the side chain at C-17. 

In their continuing work on the synthesis of pentacyclic triterpenes, Ireland s group proposed the tetracyclic ketone 69 as a key intermediate. However, such a structure could also be elaborated to the tetracyclic triterpene, ( )-shionone... 

CjoHsoO, Mr 426.73, mp. 215 C (anhydrous), 99 C (hydrate), [a]o +54 (CHCy. Tetracyclic triterpene alcohol with an extra cyclopropane ring. C. is isolated technically e.g. from the fruits of Artocarpus integri-folius, the poison nut (Strychnos nux-vomica), leaves of the potato plant (Solatium tuberosum), and the latex of Euphorbiaceae. It is present, at least in traces, in all green photosynthetically active plants since it is the first detectable cyclization product of 2,3-epoxysqua-lene in the course of the biosynthesis of cholesterol (and thus all other plant steroids) in plants. 

Step 4 Rearrangement and deprotonation of protosteryl cation gives the tetracyclic triterpene lanosterol. 

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