Ruzicka, isoprene rule

Bloch therefore suggested isoprene units could be condensed first to give squalene and then cholesterol, an extension of Ruzicka s isoprene rule for the biosynthesis of linear and cyclic terpenoids. It was then necessary to show that selectively labeled 14C-acetate could get incorporated into squalene with the correct distribution of 14C and that this squalene could give rise to cholesterol, also with the appropriate position of the 14C label. 

Terpenoids are compounds derived from a combination of two or more isoprene units. Isoprene is a five carbon unit, chemically known as 2-methyl-1,3-butadiene. According to the isoprene rule proposed by Leopold Ruzicka, terpenoids arise from head-to-tail joining of isoprene units. Carbon 1 is called the head and carbon 4 is the tail . For example, myrcene is a simple 10-carbon-containing terpenoid formed from the head-to-tail union of two isoprene units as follows. 

Ruzicka, L. (1953). The isoprene rule and the biogenesis of terpenic compounds. Experi-entia 9 357-367. 

Terpenes are most familiar, at least by odor, as compounds of the so-called essential oils obtained by steam distillation or ether extraction of various plants. Thousands of different terpenes are known. According to the isoprene rule proposed by L. Ruzicka in 1921, they can be considered to arise from head-to-tail joining of simple five-carbon isoprene (2-methyl-1,3-butadiene) units. Terpenes are subdivided into groups depending on the number of isoprene units [9]. For example, monoterpenes are 10-carbon substances biosynthesized from two isoprene units, which can be divided into aliphatic, monocyclic, or bicyclic species Some typical exponents of each monoterpene subgroup are shown in Fig 1... 

Isoprene rule. In the light of the fact that the then known mono- and sesquiterpenes were built up of two or three isoprene units, respectively, O. Wallach in 1887 prtmosed his simple isoprene rule . In 1953 L. Ruzicka formulated his biogenetic isoprene rule which proved to be a milestone in the chemistry of the terpenoids. According to this rule, all terpenoids are derived from acyclic parent structures monoterpenes are formed from geranyl pyrophosphate (GPP, Cio), sesquiterpenes from famesyl pyrophosphate (FPP,... 

About 30 000 terpenes are known at present in the literature Their basic structure follows a general principle 2-Methylbutane residues, less precisely but usually also referred to as isoprene units, (Cs), build up the carbon skeleton of terpenes this is the isoprene rule found by Ruzicka and Wallach (Table 1). Therefore, terpenes are also denoted as isoprenoids. In nature, terpenes occur predominantly as hydrocarbons, alcohols and their glycosides, ethers, aldehydes, ketones, carboxylic acids and esters. 

In 1921, Leopold Ruzicka (1887-1976) established the isoprene rule for the biosynthesis of terpenes through a formal head-to-tail coupling of isoprene units. Deviations from the rule (as in the case of chrysanthemic acid), as well as Wagner-Meerwein rearrangements, occasionally complicate the analysis. Only in the mid-1950s it could be shown that terpenes are indeed formed by active isoprene emits . [24,25]... 

Ruzicka, L., Faraday Lecture (History of the isoprene rule), Proc. Chem. Soc. (Lond.), 341-360 (1959). 

Ruzicka, L. History of the Isoprene Rule. Proceedings of the Chemical Society (London) (1959) 341. 

This chapter contains a discussion of possible ways of separating lipophilic mixtures of natural products, the components of which are built up from isoprene units in accordance with Ruzicka s isoprene rule [219]. Wallach [321] has divided the hydrocarbons and their derivatives into the following groups ... 

Wallach proposed that one isoprene (2-methyl-l, 3-butadiene) unit of five carbon atoms could serve as this function. This idea was eventually elaborated on by Ruzicka and Bloch into the isoprene rule. Eventually, as we will see, the family of terpenes (Cio), sesquiterpenes (C15), diterpenes (C20), sesterpenes (C25), triter-penes (C30), and truly large compounds (polymers) found in latex and gutta-percha comprises tens of thousands of individual, unique compounds all of which may be considered as derived from isoprene (2-methyl-l,3-butadiene) and that the pair of C5 isomers, isopentenyl diphosphate and dimethylallyl diphosphate, compounds linked by interconversion (Scheme 11.41) under the influence of the isopentenyl isomerase (EC 5.3.3.1) serve as the biochemical parents to the family. ... 

Ruzicka, L. Experientia, 1953,9,357 where the isoprene rule is defined. 

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