Phenols simple

Phenols are one of the largest gronps of secondary plant constitnents. They are aromatic alcohols since the hydroxyl gronp is always attached to a benzene ring. 

Like all alcohols the names of phenols always end in the letters oP. In addition the ring system may bear other snbstitntes, especially methyl gronps. 

Simple phenols consist of an aromatic ring in which a hydrogen is replaced by a hydroxyl gronp. Their distribntion is widespread among all classes of plants. General properties of simple phenols are bactericidal, antiseptic and anthelmintic. Phenol itself is a standard for other antimicrobial agents. 

The simplest phenols are Cg strnctnres consisting of an aromatic ring with hydroxyl gronps attached. These inclnde pyrogallol and hydroquinone. 

Addition of a carboxyl gronp to the basic phenol strnctnre prodnces a gronp of CgCj componnds, inclnding some of widespread distribntion among plants and with important therapentic activity. The most important of these are gallic acid and salicylic acid. 

The enormous reactivity of the phenolic ring towards electrophilic halogena-tion has led to a multitude of natural halogenated phenols, both terrestrial and marine (1). 

The previously reported 2,6-dichlorophenol, which is a sex pheromone of several species of tick (1), is also produced by the African tick Amblyomma hebraeum (1662, 1663). This pheromone has been used to control the African bont tick on 

The wood-rotting fungi of genus Bjerkandera produce a number of chlorinated phenols and derivatives (398,1677). 

The brown alga Leathesia nana from the gulf of the Yellow Sea in China has yielded the new bromophenols 1855 and 1856 (1736-1738), and the Chinese red 

A study of the natural radiocarbon (14C) in the acorn worm Saccoglossus bromophenolosus, which was collected off the Maine coast, revealed that the 2,4-dibromophenol produced by these worms is of recent origin, in contrast to that from petroleum-derived anthropogenic 2,4-dibromophenol (1746). Thus, this result combined with the earlier study (1223) supports a natural source of 2,4-dibromophenol in these animals. It should be noted that the more recent radiocarbon work utilizes improved methodology (1746). 

---

The chemical resistance of the mouldings depends on the type of filler and resin used. Simple phenol-formaldehyde materials are readily attacked by aqueous sodium hydroxide solution but eresol- and xylenol-based resins are more resistant. Provided the filler used is also resistant, phenolic mouldings are resistant to acids except 50% sulphurie aeid, formic acid and oxidising acids. The resins are stable up to 200°C. Some reeently developed grades of moulding compounds are claimed to be capable of exposure to 300°C for short periods. 

The TBDPS ether has been used for the monoprotection of a catechol (TBDPSCl, Im, DMF, 5 h, 83% yield) or simple phenol protection. It is cleaved with Bu4N F- (THF, 94% yield). ... 

Cured phenol-formaldehydes are resistant to attack by most chemicals. Organic solvents and water have no effect on them, though they will swell in boiling phenols. Simple resins are readily attacked by sodium hydroxide solutions, but resins based on phenol derivatives, such as cresol, tend to be less affected by such solutions. Simple phenol-formaldehyde polymers are resistant to most acids, though formic and nitric acids will tend to attack them. Again, cresol-based polymers have resistance to such attack. 

For most simple phenols this equilibrium lies well to the side of the phenol, since only on that side is there aromaticity. For phenol itself, there is no evidence for the existence of the keto form. However, the keto form becomes important and may predominate (1) where certain groups, such as a second OH group or an N=0 group, are present (2) in systems of fused aromatic rings and (3) in heterocyclic systems. In many heterocyclic compounds in the liquid phase or in solution, the keto form is more stable, although in the vapor phase the positions of many of these equilibria are reversed. For example, in the equilibrium between 4-pyridone (118) and 4-hydroxypyridine (119), 118 is the only form detectable in ethanolic solution, while 119 predominates in the vapor phase. " In other heterocycles, the hydroxy-form predominates. 2-Hydroxypyridone (120) and pyridone-2-thiol (122) are in equilibrium with their tautomers, 121 and 123, respectively. In both cases, the most stable form is the hydroxy tautomer, 120 and 122. ... 

Ethell BT, Ekins S, Wang J, Burchell B. Quantitative structure activity relationships for the glucuronidation of simple phenols by expressed human UGT1A6 and UGT1A9. Drug Metab Dispos 2002 30 734-8. 

Tenerife and La Palma, revealed the existence of luteolin and an array of simple phenolic derivatives as well as three known phytosterols, B-amyrin, sitosterol, and stigmasterol. The phenols identified comprised a set of phenylpropanoids myristicin [566] (see Fig. 6.16 for structures 566-573), methyleugenol [567], todadiol [568], todatriol [569], crocatone [570], elemicin [571], apiole [572], and the coumarin scopoletin [573]. The occurrence of these compounds is recorded in Table 6.5. The differences between the two profiles were taken by Gonzalez and his co-workers... 

Table 6.5 Distribution of simple phenols and phytosterols in Todaroa aurea (from Gonzalez etal., 1988)...

Fig. 7.3 Compounds 590-601, flavonoids of Chrysosplenium, and simple phenolic derivatives from Encelia...

Green tea consists of a wealth of simple phenolics (monomers), whereas black tea provides more complex polyphenols (dimers and polymers). It was found that with lipids the simple compounds were more effective antioxidants, while under aqueous conditions, polymers tended to have more activity. Weisburger (2001) suggested that polymers formed from a 2-5 unit polymerisation state seemed to be optimal, probably because the monomer is metabolised and excreted too rapidly, whereas the higher 6-10 unit polymers may suffer from difficulty in penetrating cellular membranes and be poorly absorbed. 

As Einhellig (48) correctly stated, "Unless cooperative research between chemists and physiologists is conducted, we will continue to be left with the notion that an array of simple phenols cannon to a wide array of soils and situations are the major chemical allelopa-thic agents." As for the importance of the chemical identity, Putnam and Duke (17) expressed it very well "after all chemicals are identified, studies can be made on genetics, specificity, environmental influences and environmental consequences."... 

The most likely explanation for these results is that simple phenolics inhibit a very large array of enzymes in vitro. The most likely explanation for the CNS effects of Uncaria rynchophylla would be that indole alkaloids, such as dihydrocorynanteine or hirsutine (32), interact with the central neurotransmission and possibly the serotonin ergic system. 

Decarboxylase Decarboxylation of amino adds and simple phenolic adds, primarily p-hydroxylated L-dopa, tyrosine... 

Simple phenolics and their derivatives (benzoic, gallic, ellagic, gallotannins and ellagitannins), flavonoids and condensed tannins... 

Food and plant phenolics are commonly detected using DAD detectors (Tan and others 2008). Photodiode array detection allows collection of the entire UV spectrum during the elution of a chromatographic peak, which makes it possible to identify a phenolic compound by its spectra. Simple phenols, phenolic acids, flavanones, benzophenones, isoflavones, and flavan-3-ols have maximum absorbance at 280 nm, hydroxycinnamic acids at 320 nm, flavonols, flavones, and dihydroflavonols at 365 nm, and anthocyanins at 520 nm (Ibern-G6mez and others 2002 Merken Hand Beecher 2000). Hydrolyzable tannins show a characteristic shoulder at 300 nm, suitable for identifying them (Arapitsas and others 2007). For stilbenes, maximum absorbance of trans-forms are at 306 nm and at 285 nm for cA-forms (Lamuela-Raventos and others 1995). 

Virgin olive oil contains considerable amounts of simple phenols that have a great effect on the stability/sensory and nutritional characteristics of the product. Some of the most representative are hydroxytyrosol (3,4-dihydroxyphenylethanol) and tyrosol (4-hydroxyphenylethanol) however, phenolic compounds are removed when the oil is refined (Tovar and others 2001). The phenolic content of virgin olive oil is influenced by the variety, location, degree of ripeness, and type of oil extraction procedure used, and that is why hydroxytyrosol can be considered as an indicator of maturation for olives (Esti and others 1998). Hydroxytyrosol concentrations are correlated with the stability of the oil, whereas those of tyrosol are not (Visioli and Galli 1998). 

Simple phenolic compounds include (1) the phenylpropanoids, trans-cinnamic acid, p-coumaric acid and their derivatives (2) the phenylpropanoid lactones called coumarins (Fig. 3.4) and (3) benzoic acid derivatives in which two carbons have been cleaved from the three carbon side chain (Fig. 3.2). More complex molecules are elaborated by additions to these basic carbon skeletons. For example, the addition of quinic acid to caffeic acid produces chlorogenic acid, which accumulates in cut lettuce and contributes to tissue browning (Fig. 3.5). 

It seems that the effect of the induction of phenol-content increment by high oxygen atmospheres is affected also by the exposure time of the product to the given atmosphere (Ayala-Zavala and others 2007). Awad and others found no losses of flavonoids in apples stored under conventional or controlled atmosphere (Awad and others 2000). No changes in the concentration of simple phenols, flavonoids, and anthocyanins were observed for Delicious and Ralls apples held for 4 to 5 months under refrigeration (Ju and others 1996). However, they found a decrease in simple phenols in earlier harvested apples after 3 months of cold storage. However, after 7 days at 20°C storage, phenols and flavonoid content decreased rapidly. 

Ju Z, Yuan Y, Liu C, Zhan S and Wang M. 1996. Relationships among simple phenol, flavonoid and anthocyanin in apple fruit peel at harvest and scald susceptibility. Postharvest Biol Technol 8 83—93. 

SPOELSTRA, S.F. (1977). Simple phenols and indoles in anaerobically stored piggery wastes. Journal of the Science of Food and Agriculture 28, 415-423. 

This paper reports on the aspects of dust formation in livestock buildings, the material composition of the dust, the emission of dust-bome odourants like volatile fatty acids (VFA) and simple phenols and indoles from piggeries, the importance of particle-borne... 

Cytochrome P4502E1, also microsomally located, catalyzes the hydroxylation of phenol to form hydroquinone (and to a much lesser extent catechol), which is then acted upon by the phase II enzymes (Benet et al. 1995 Campbell et al. 1987 Gut et al. 1996 McFadden et al. 1996). All three enzyme systems are found in multiple tissues and there is competition among them not only for phenol but for subsequent oxidative products, like hydroquinone. As a consequence, the relative amount of the products formed can vary based on species, dose and route of administration. In vivo, the gastrointestinal tract, liver, lung, and kidney appear to be the major sites of phenol sulfate and glucuronide conjugation of simple phenols (Cassidy and Houston 1984 Powell et al. 1974 Quebbemann and Anders 1973 ... 

---