Triterpenoids:

Triterpenoids (C30 compounds) are the most ubiquitous of the terpenoids and are found in both terrestrial and marine flora and fauna (Mahato et al., 1992). Diterpenoids and triterpenoids rarely occur together in the same tissue. In higher plants, triterpenoid resins are found in numerous genera of broad-leaved trees, predominantly but not exclusively tropical (Mills and White, 1994 105). They show considerable diversity in the carbon skeleton (both tetracyclic and pentacyclic structures are found) which occur in nature either in the free state or as glycosides, although many have either a keto or a hydroxyl group at C-3, with possible further functional groups and/or double bonds in the side-chains. 

A number of important resins are composed of triterpenoids, including the dammar resins which derive from a sub-family of the family Dipterocarpaceae. Dammar resins are fluid, balsamic oleoresins highly suited for caulking and waterproofing. Frankincense (olibanum) is known as a gum-resin collected from various Boswellia spp. and contains amyrin epimers and triterpenoid acids. The gum component is polysaccharide in origin and is water soluble. The Anacardiaceae family contains the genus Pistacia (Mills and White, 1977 21 Mills and White, 1989). 

Newly described triterpenoids from lichens are summarized in Table 10. 

Zeorin and hopan-3p,6a,15P,22-tetrol were found in the higher plants Iris missouriensis 737), Tripterygium regelii 435) and Mollugo pentaphylla 663) respectively. The C-70 polyterpene ficaprenol (588) was found in serveral lichens 618). 

16P-diol 3 P-Methoxy serrat-14- 571 Evernia prunastri (684a) 

Bitter and nonbitter forms of the many Cucur-bitaceae are known. The bitter forms contain cu-curbitacins (III) in fruits and seeds. For example, Citrullus lanatus (watermelon) contains HIE in glycosidic form while Cucumis sativus (cucumber) contains IOC and Cucurbita spp. (pumpkin) contains IIIB, D, E and I (cf. Formula 18.6). 

L-Malic and citric acids are the major organic acids of fruits (Table 18.13). Malic acid is predominant in pomme and stone fruits, while citric acid is most abundant in berries, citrus and tropical fruits. (2R 3R)-Tartaric acid occurs only in grapes. Many other acids, including the acids in the citric acid cycle, occur only in low amounts. Examples are cis-aconitic, succinic, pyruvic, citramalic, fumaric, glyceric, glycolic, glyoxylic, isocitric, lactic, oxalacetic, oxalic and 2-oxoglutaric acids. In fruit juices, the ratio of citric acid to isocitric acid (examples in Table 18.14) serves as an indicator of dilution with an aqueous solution of citric acid. 

The common precursor in the biosynthesis of limonoids and cucurbitacins is squalene-2,3-oxide (IV). Based on some identified intermediary compounds, the biosynthetic pathway is probably as postulated in Reaction 18.7. 

The biogenetic-type rearrangement of terpenoids has been reviewed.  

Further detailed study of the substrate specificity of yeast squalene synthetase has been reported (see Vol. 7, p. 130). The enzyme is very sensitive to changes in substrate. For example, 10,11-dihydrofarnesyl pyrophosphate was converted into 2,3,22,23-tetrahydrosqualene with only 60% of the efficiency of farnesyl pyrophosphate whereas 6,7-dihydro- and 6,7,10,11-tetrahydro-farnesyl pyrophosphates were not metabolized. The first of the two binding sites has a greater preference for farnesyl pyrophosphate and this accounts for the formation of the unsymmetrical squalene product when mixtures of farnesyl pyrophosphate and a modified substrate are used. The importance of the methyl groups, especially that at C-3, for binding is emphasized by the low efficiency of conversion of 3-desmethylfarnesyl, , -3-methylundeca-2,6-dien-l-yl (1), and E,E-7-desmethylfarnesyl pyrophosphates. The prenylated cyclobutanones (2) and (3) 

The biosynthesis of triterpenoids in the latex of Hoya australis, H. camosa. Euphorbia pulcherrima, and related species has received detailed attention.  

The timing of triterpenoid biosynthesis in developing Sorghum bicolor grains and in Pinuspinea has been investigated. 

The detailed structure of caldariellaquinone (12), a unique benzo[6]thiophen-4,7-quinone from Caldariella acidophila, has been elucidated. Feeding experiments with C-labelled acetate helped to define the nature and biosynthetic origin of the C30 isoprenoid chain. 

This chapter follows the pattern of last year s Report with the addition of a section on Triterpenoid Saponins. The highlight of this year s Report is undoubtedly the total synthesis of /-quassin by Grieco and his co-workers.1 

Reviews have appeared on the occurrence of triterpenoid saponins and sapo-genins,2 the mass spectra of pentacyclic triterpenoids,8 and the possible role of triterpenoids as membrane components.4 The plenary lectures from the 12th IUPAC Symposium on the Chemistry of Natural Products have been published.5 

The biosynthesis of triterpenoids is discussed at some length in a new book.8 The bacterium Acetobacter pasteurianum forms hopanoids such as diploptene (1) by 

The bacterium Methylococcus capsulatus is unique among prokaryotes in that it produces not only hopanoids but also lanosterol derivatives. Evidence for the 

Details have been published of the biosynthesis of olean-12-ene and urs-12-ene type triterpenoids in tissue cultures of lsodon japonicus (Labiatae).10 The results are fully in accord with the original biogenetic postulates of Ruzicka and his colleagues.11 By using [5-13C, 5-2H2]MVA as substrate it was shown that, as expected, both squalene 2,3-epoxides [part structures (12) and (13)] are involved in the biosynthesis of 2a-hydroxyursolic acid (14), 3-epimaslinic acid (15), and j3-sitosterol in I. japonicus. The 13C n.m.r. spectra of (14) and (15) suggested 

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Farnesol pyrophosphate is an immediate precursor of squalene, the key intermediate in steroid and triterpenoid biogenesis, which arises from the coupling of two farnesol pyrophosphate molecules or of C,s units derived therefrom. The numerous types of sesquiter-penoid carbon skeletons represent various modes of cyclization of farnesol (sometimes with rearrangement) and it is probable that farnesol pyrophosphate is also the source of these compounds. 

Soybeans and peanuts also contain saponins, which are glucoside derivatives of triterpenoid alcohols (37). Saponins range from 0.09 to 0.32% in 457 soybean varieties (38). 

Sterols, triterpenoids (e.g. lupeol), primary and secondary alcohols... 

Terpenes (and terpenoids) are further classified according to the number of 5-carbon units they contain. Thus, monoterpenes are 10-carbon substances biosynthesized from two isoprene units, sesquiterpenes are 15-carbon molecules from three isoprene units, diterpenes are 20-carbon substances from four isoprene units, and so on. Monoterpenes and sesquiterpenes are found primarily in plants, but the higher terpenoids occur in both plants and animals, and many have important biological roles. The triterpenoid lanosterol, for example, is the precursor from which all steroid hormones are made. 

The terpenoid precursor isopentenyl diphosphate, formerly called isopentenyl pyrophosphate and abbreviated IPP, is biosynthesized by two different pathways depending on the organism and the structure of the final product. In animals and higher plants, sesquiterpenoids and triterpenoids arise primarily from the mevalonate pathway, whereas monoterpenoids, diterpenoids, and tetraterpenoids are biosynthesized by the 1-deoxyxylulose 5-phosphate (DXP) pathway. In bacteria,... 

Further combination of GPP with another IPP gives the C15 unit farnesyl diphosphate (FPP), and so on, up to C25. Terpenoids with more than 25 carbons—that is, triterpenoids (C30) and tetraterpenoids (C40)—ate synthesized by dimerization of Cj5 and C2q units, respectively (Figure 27.8). Triterpenoids and... 

Steroids are heavily modified triterpenoids that are biosynthesized in living organisms from farnesyl diphosphate (Cl5) by a reductive dimerization to the acyclic hydrocarbon squalene (C30), which is converted into lanosterol (Figure 27.12). Further rearrangements and degradations then take place to yield various steroids. The conversion of squalene to lanosterol is among the most... 

Triterpenoid, 1071 tRNA, see Transfer RNA Trypsin, peptide cleavage with, 1033 Tryptophan, pKa of, 52... 

The biomimetic approach to total synthesis draws inspiration from the enzyme-catalyzed conversion of squalene oxide (2) to lanosterol (3) (through polyolefinic cyclization and subsequent rearrangement), a biosynthetic precursor of cholesterol, and the related conversion of squalene oxide (2) to the plant triterpenoid dammaradienol (4) (see Scheme la).3 The dramatic productivity of these enzyme-mediated transformations is obvious in one impressive step, squalene oxide (2), a molecule harboring only a single asymmetric carbon atom, is converted into a stereochemically complex polycyclic framework in a manner that is stereospecific. In both cases, four carbocyclic rings are created at the expense of a single oxirane ring. 

Sometimes several of these rearrangements occur in one molecule, either simultaneously or in rapid succession. A spectacular example is found in the triterpene series. Friedelin is a triterpenoid ketone found in cork. Reduction gives 3p-friedelanol (47). When this compound is treated with acid, 13(18)-oleanene (48) is formed. In this case seven 1,2 shifts take place. On removal of H2O from position 3 to leave a positive charge, the following shifts occur hydride from 4 to 3 methyl... 

ATA A, NAZ s, CHOUDHARY M I, ATTA-UR-RAHMAN, SENER B, TURKOZ s (2002) New triterpenoidal alkaloids from Buxus sempervirens. Z Naturforsch [C]. 57 21-8. 

GOODWIN T w and goad l j (1971) Carotenoid and triterpenoids , in Hulme A C, The Biochemistry of Fruits and their Products, London, Academic Press, 305-28. 

Pentacyclic triterpenoids-lantadenes Lantana camara var. aculeate SiOj GF Petroleum + AeOEt + AcOH UV Purification, HPLC 43 ... 

Triterpenoids Picea glehni stem bark SiOj Hx + AcOEt uv Identification 58 ... 

Apart from the use and need as fragrances, the resins are marketed for medicinal use as antiarthritic and antiinflammatory pharmaceutical products. The pharmacological effects are mainly attributed to the presence of the nonvolatile pen-tacyclic triterpenoid boswellic acids. This class of ingredients is not present in the actual valuable B. frereana species hence, B. frereana plays no part in the pharmaceutical area. 

Gunatilaka, A. A. L. Triterpenoid quinonemethide and related compound (celastroloids). In Progress in the Chemistry of Organic Natural Products Hertz, W. Kirby, G. W. Moore, R. E. Steglich, W. Tamm, C., Eds. Springer-Verlag New York, 1996 Vol. 67, 1-123. 

Dirsch, V. M. Kiemer, A. K. Wagner, H. Vollmar, A. M. The triterpenoid quinonemethide pristimerin inhibits induction of inducible nitric oxide synthase in murine macrophages. Eur. J. Pharm. 1997, 336, 211-217. 

Sotanaphun, U. Suttisri, R. Lipipun, V. Bavovada, R. Quinone-methide triterpenoids from Glyptopetalum sclerocarpum. Phytochemistry 1998, 49, 1749-1755. 

Mean-Rejon, G. J. Perez-Espadas, A. R. Moo-Puc, R.E. Cedillo-Rivera, R. Bazzocchi, I. L. Jimenez-Diaz, I. A. Quijano, L. Antigiardial activity of triterpenoids from root bark of Hippocratea excelsa. J. Nat. Prod. 2007, 70, 863-865. 

Murayama, T. Eizuru, Y. Yamada, R. Sadanari, H. Matsubara, K Rukung, G. Tolo,F. M. Mungai, G. M. Kofi-Tsekpo, M. Anticytomegalovirus activity of pristimerin, a triterpenoid quinone methide isolated from Maytenus heterophylla (Eckl. Zeyh.). Antiviral Chem. Chemother. 2007, 18, 133-139. 

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