Skeletons representative compounds

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. 

The terpenoids form a large and structurally diverse family of natural products derived from C5 isoprene units (Figure 5.1) joined in a head-to-tail fashion. Typical structures contain carbon skeletons represented by (Cs) , and are classified as hemiterpenes (C5), monoterpenes (C10), sesquiterpenes (C15), diterpenes (C2o), sesterterpenes (C25), triterpenes (C30) and tetraterpenes (C40) (Figure 5.2). Higher polymers are encountered in materials such as rubber. Isoprene itself (Figure 5.1) had been characterized as a decomposition product from various natural cyclic hydrocarbons, and was suggested as the fundamental building block for these compounds, also referred to as isoprenoids . Isoprene is produced naturally but is not involved in the formation of... 

Yohimbine alkaloids possess a characteristic pentacyclic indole skeleton. Representative members of the family include the rauwolfia (reserpine and deserpidine) and the yohimbines. A wide range of medicinal properties has been associated with these compounds and extensive studies have been carried out on the synthesis of the yohimbine alkaloids, including enantioselective syntheses [13,14]. In our approach, we view the acetylenic sulfoxide as a two-carbon synthon for the C3-C14 segment of the pentacyclic system (see 27). The chirali-... 

Fig. 1. Skeletons of the macrolides. The compound name for each ring size is the representative compound for each class. These compounds are described in the text.

Among the antimalarial active quassinoids, bruceolide (248) is one of the representative compounds as a common core skeleton. 

Quite different are the chemical features of some newer antiperoxidative triterpenoids from Trypterigium wilfordii, because they have highly unsaturated A and B rings with a quinonoid-like structure over a friedooleanane skeleton. The main datum to be noted is that celastrol, the most representative compound of this series, inhibits mitochondrial LP, with an IC50 - 7 iM. Its potency is then 15 times higher than that of a-tocoferol. Furthermore, it has been observed that while celastrol and its acetyl derivative affect the radical chain reaction in a biphasic manner, a-tocoferol and pristimerin, a celastrol-methyl ester, do it monotonously. 

In the year 2010, a novel C2o-diterpenoid alkaloid named piepunine (70) has been isolated from A. piepunense containing both atisine and denudatine skeletons [48]. Compound 70 represents the first example of this type. 

Members of the yohimbine alkaloid family possess a characteristic penta-cyclic indole skeleton 1. Representative compounds in this family include the Rauwolfia alkaloids, such as reserpine (2) and deserpidine (3), and the yohimbines (4-9). These compounds exhibit a wide range of medicinal properties (1,2). Reserpine, for example, has been used extensively in the treatment... 

The distance between the two reactive centers in each component is given by numbering the skeleton atoms for example, 1,3 [n,n] represents a 1,3-dinucleo-philic compound For further details see reference 79. 

Suppose a reaction is performed on a substrate molecule that can be represented as XGY, where Y is the site of the reaction, X a variable substituent, and G a skeleton group to which X and Y are attached, and we find that changing X from H to CH3 results in a rate increase by a factor, say, 10. We would like to know just what part of the increase is due to each of the effects previously mentioned. The obvious way to approach such a problem is to try to find compounds in which one or two of the factors are absent or at least negligible. This is not easy to do acceptably because factors that seem negligible to one investigator do not always appear so to another. The first attempt to give numerical values was that of Hammett. For the cases of m-and P-XC6H4Y, Hammett set up the equation... 

Bond-line drawings show the carbon skeleton (the connections of all the carbon atoms that build up the backbone, or skeleton, of the molecule) with any functional groups that are attached, such as - OH or -Br. Lines are drawn in a zigzag format, where each comer or endpoint represents a carbon atom. For example, the following compound has 7 carbon atoms ... 

This next example involves the well-known plant kawa. A psychoactive beverage made from the roots of this plant is used widely in the islands of the southwestern Pacific Ocean either for ritualistic or routine consumption. Kava is the common name for Piper methysticum Forst. f. from which several compounds responsible for the pharmacological activity have been isolated and identified. Representative structures of the family of styrylpyrones, commonly called kavalactones, are given in Fig. 6.6. The compounds are based upon a carbon skeleton consisting of a styryl function (C C ) attached to a six-membered lactone ring. The fundamental compound, kawain, is shown as structure [547]. Structural variants include... 

In general, the triarylmethane leuco skeleton can be represented by structures 1-4. Traditional leuco di- and triphenylmethane dyes frequently include compounds of type 1 and 3. The closely related compounds 2 and 4 are derived from 1 and 3. Another closely related type is the lactone or phthalide 5 (see Chapter 4). In all of these leuco dyes, one or more of the phenyl rings can be replaced by a hetaryl ring or by a fused aromatic ring such as a naphthalene. 

Dicyano-substituted triafulvenes react with enamines to produce exclusively the cross-conjugated dicyanomethylene compounds 519, whose formation can be rationalized by a methylene bicyclo(2,l,0)pentane intermediate 51879 296 Since cyclanone enamines 520 and other cyclic enamines 522 react analogously, this C-C-insertion 237) of the triafulvene ring skeleton into the enamine C=C bond represents a versatile ring expansion mode (C + C3), which makes accessible a series of unsaturated medium-ring compounds (521/523) that are otherwise difficult to synthesize. 

The acyclic (ammonioorganyl)tetrafluorosilicates 4,18 5,19 6-8,20 and 9-1621 represent zwitterionic A5S/-silicates with an Si 4C skeleton. Compounds of this particular formula type can be synthesized as demonstrated in Scheme 2 for compounds 6 (with NH group) and 7 (without NH group). Typically, the syntheses were carried out at 0°C using mixtures of hydrofluoric acid and ethanol as the HF source. 

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