Isoprene-derived compounds

Organic Syntheses and Organic Reactions, Jack and his students published research papers on organo-boron compounds, furan derivatives, dienes, ketene derivatives, the structure of gliotoxin, and biosynthesis of isoprene derivatives. 

Using an aliphatic monoterpene like myrcene as reaction partner for 1 the formation of silacylobutanes E/Z-1 and E/Z-S in a ratio of 34 30 22 14 is observed an ene product could not be detected. In this case myrcene behaves like an isoprene derivative, which forms only [2+2] cycloadducts with 1 [8]. The reaction with 2, however, yields a product mixture containing the silacyclobutanes E/Z-9 and E/Z-10, the Diels-Alder compounds 11 and 12, the ene product 13, and the silene dimer 7Z-14 [14, 15] (Fig. 2). 

Terpenes are a large class of hydrocarbon compounds constructed from five-carbon isoprene units that are combined to produce a great variety of skeletons, which are then acted upon by various enzymes to add functionality and altered oxidation. Terpene-derived compounds possess a broad array of activities and are produced by animal, plant, and bacterial sources. This pathway has been reviewed extensively elsewhere" but, briefly, involves chain extension of isoprene units into phosphorylated chains in multiples of five carbons. The initially formed linear prenyl chains are then acted upon by other enzymes resulting in cyclization and additional modifications. For example, one class of modification involves oxygenation on the ring before cyclization to yield lactone and furan moieties, or postcyclization to yield carbonyl and alcohol functionalities. 

Cholesterol serves as the biosynthetic precursor for several vital compounds, including a variety of steroid hormones and bile acids. Many of these compounds, and many other polyisoprenoid compounds biosynthetically related to cholesterol, act biologically as important regulatory compounds [105]. In mammals such regulatory compounds include steroid hormones and vitamins A and D. Steroids and other isoprene derivatives also play important regulatory roles in other phyla. Several insect hormones, for example, are isoprenoid derivatives [106] (cf. Chapter 8). Memy of the floral scents of plants are isoprene derivatives. 

Hayakawa et al. 1991a,b) as an antibiotic, although it has alkaloidal attributes. We chose to include this compound here to illustrate an interesting utilization of HMBC data to establish the structure of a long, isoprene-derived chain connecting two portions of the molecular structure. 

Early studies indicated that terpenes were composed of five carbon units. By 1860, isoprene, a compound with the empirical formula C5H8, could be derived by pyrolysis of turpentine and rubber. Further, isoprene could be transformed into a C10H16 compound that subsequently decomposed back to the original five-carbon unit. Wallach recognized that terpenes could be subdivided into several groups hemiterpenes, true terpenes, sesquiterpenes, and diterpenes. In 1887, he proposed that monoterpenes (true terpenes) as well as other terpenoids were composed of isoprene units, a concept that became known as the isoprene rule (Wallach, 1887). The structure of isoprene was not solved until much later (Spurgeon and Porter, 1981). 

Terpene compounds were also examined for inducing activity because they, like the steroids, are isoprene derivatives, although representing simpler molecules than the steroids. The basic structural... 

The compound of simplest structure which had inducing activity several times that of AIA was cyclopentadecanone (14), otherwise known as Exaltone, the perfumery fixative. This compound consists of a large saturated ring with one carbonyl group, and may be written to resemble a steroid in configuration. The most active of the isoprene derivatives was -ionone (15) it was about ten times as active as AIA in porphyrin induction. 

Nitriles can be used as starting material for the bisdithioesters (62 n = 4, 5, lO), whereas the derivatives with shorter chain lengths (62 n = l-3), as well as methyl dithiocinnamate (63), are accessible from /VA -disubstituted thioamides via the corresponding imidothioate iodides. Methyl di-thioacrylate (65), the simplest unsaturated dithioester, was prepared by flash vacuum thermolysis of a precursor dithioester (64), which had been obtained from the corresponding nitrile (equation 64). It can be isolated as a red monomeric compound at 77 K but dimerizes rapidly at room temperature. The p,7-unsaturated isoprene derivative (66) and the methyl 2-arylpropanedithioates (67) were prepared from phenyl isothiocyanate and used as educts for syntheses of lavandulal and ar-curcumene. Also ethyl furane 3-carbodithioate (68), as prepared from the nitrile, has found application in syntheses of the natural products egona ketone and ar-turmerone. ... 

Another group of isoprene polymerization catalysts is based on alanes and TiCl. In place of alkyl aluminum, derivatives of AlH (alanes) are used and react with TiCl to produce an active catalyst for the polymerization of isoprene. These systems are unique because no organometaHic compound is involved in producing the active species from TiCl. The substituted alanes are generally complexed with donor molecules of the Lewis base type, and they are Hquids or soHds that are soluble in aromatic solvents. The performance of catalysts prepared from AlHCl20(C2H )2 with TiCl has been reported (101). 

Steroids (1) are members of a large class of lipid compounds called terpenes that are biogenicaHy derived from the same parent compound, isoprene, C Hg Steroids contain or are derived from the perhydro-l,2-cyclopentenophenanthrene ring system (1) and are found in a variety of different marine, terrestrial, and synthetic sources. The vast diversity of the natural and synthetic members of this class depends on variations in side-chain substitution (primarily at C17), degree of unsaturation, degree and nature of oxidation, and the stereochemical relationships at the ring junctions. 

Isoprene with Alano-derivatives and Titanium Compounds. Makromol. Chem. 71, 134 (1964). 

Treatment of phosphorus trichloride with isoprene in the presence of acetone leads to 1-chlorophospholen 1-oxides (33).33 Evidence has been presented that the diene reacts first with the trichloride to produce (34), which then reacts with acetone.33 l-Bromo-3,4-dimethyl-A3-phospholen (35) does not form a spiro-compound with 2,3-dimethylbuta-l,3-diene, although the bisphospholen derivative (36) has been isolated after hydrolytic work-up.34... 

Interestingly, various phosphonium salts have been applied [13] as constituents of palladium catalysts for hydrodimerization of butadiene and isoprene about the same time when the results of Kuraray were disclosed. These were obtained by quatemization of aminoalkylphosphines with methyl iodide or HQ (Ph2P-R-NH2 type compounds are known to yield phosphonium salts with these reagents). Although the catalysts prepared in situ from [PdCU] were reasonably active (TOF-s of 10-20 h ) the reactions always yielded complex product mixtures with insufficient selectivity towards the desired 1,7-octadienyl derivatives. 

Formally, isoprenoids are derived from a single common building block, isoprene (2-methyl-l,3-butadiene), a methyl-branched compound with five C atoms. Activated isoprene, isopentenyl diphosphate, is used by plants and animals to biosynthesize linear and cyclic oligomers and polymers. For the isoprenoids listed here—which only represent a small selection—the number of isoprene units (1) is shown. 

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. 

In similar fashions, the core pathway up to C25 compounds (five isoprene units) is formed by sequential addition of C5 moieties derived from IPP to a starter unit derived from DMAPP. Thus, sesquiterpenes are formed form the precursor 2E, hS-farnesyl pyrophosphate (FPP), and diterpenes from 2E, 6E, IO -geranylgeranyl pyrophosphate (GGPP). The parents of triterpenes and tetraterpenes are formed by reductive coupling of two FPPs or GGPPs, respectively. Rubbers and other polyisoprenoids are produced from repeated additions of C5 units to the starter unit GGPP. 

Schoenmakers et al. [72] analyzed two representative commercial rubbers by gas chromatography-mass spectrometry (GC-MS) and detected more than 100 different compounds. The rubbers, mixtures of isobutylene and isoprene, were analyzed after being cryogenically grinded and submitted to two different extraction procedures a Sohxlet extraction with a series of solvents and a static-headspace extraction, which entailed placing the sample in a 20-mL sealed vial in an oven at 110°C for 5,20, or 50 min. Although these are not the conditions to which pharmaceutical products are submitted, the results may give an idea of which compounds could be expected from these materials. Residual monomers, isobutylene in the dimeric or tetrameric form, and compounds derived from the scission of the polymeric chain were found in the extracts. Table 32 presents an overview of the nature of the compounds identified in the headspace and Soxhlet extracts of the polymers. While the liquid-phase extraction was able to extract less volatile compounds, the headspace technique was able to show the presence of compounds with low molecular mass... 

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