Simple lignan

Simple lignans involving a Phe-C -C -Phe structure are illustrated by the antioxidant and Ca2+ channel blocker nordihydroguaiaretic acid (NDGA) (3,4-dihydroxyphenyl-CH2-CH(CH3)-CH(CH3)-CH2-(3, 4 -dihydroxyphenyl)), the bitter-tasting phyllanthin and the cAMP phosphodiesterase inhibitor ar-hinokiresinol. Simple lignans of the C3—Phe—Phe—C3 kind are illustrated by the antibacterials honokiol and the protein kinase inhibitor magnolol. 

The simple lignan nordihydroguaiaretic acid (NDGA) from chaparral Larrea tridentata (Zygophyllaceae) is a potent antioxidant. 

The lignan carpanone 1 would present a formidable synthetic challenge if it were to be constructed from simple starting materials in a linear, stepwise manner. It can, however, be assembled rapidly by the following sequence of four simple reactions (none of the intermediates need be rigorously purified) (i) alkylation of 3,4-methylenedioxyphenol with allyl... 

Further examples of oxidative arylic coupling within this family of lignan precursors include the preparation of (+)-schizandrin (169) and (+)-gomisin A (170) (Figure 5), as published by Tanaka and co-workers. In this instance, the key Ar-Ar coupling step with 194 was realized using either ruthenium tetrakis(trifluoroacetate) or iron perchlorate (Scheme 47) [124, 131-133]. As pointed out by the authors, this result was noteworthy as this simple... 

It has been noted that the chemical diversity of plant phenolics is as vast as the plant diversity itself. Most plant phenolics are derived directly from the shikimic acid (simple benzoic acids), shikimate (phenylpropanoid) pathway, or a combination of shikimate and acetate (phenylpropanoid-acetate) pathways. Products of each of these pathways undergo additional structural elaborations that result in a vast array of plant phenolics such as simple benzoic acid and ciimamic acid derivatives, monolig-nols, lignans and lignin, phenylpropenes, coumarins, stilbenes, flavonoids, anthocyanidins, and isollavonoids. 

In connection with the synthesis of podophyllum lignans, ester (62) was deprotonated and the resulting enolate condensed with 3,4,5-trimethoxybenzaldehyde to give a 1 1 mixture of diastereomeric aldols (equation 68). The structure of (63) was established by X-ray analysis the other diastereomer was assigned the 2,3-anti relative stereochemistry (64) on circumstantial evidence. It was suggested that the 1 1 mixture of isomeric products results from a 1 1 mixture of the ( )- and (Z)-enolate, each of which shows complete simple and diastereofacial selectivity in its reactions with 3,4,5-trimethoxybenzaldehyde. For this to be true, it is also necessary that the ( )-enolate reacts through a non-Zimmerman , boat-like transition state, whereas the (Z)-enolate reacts through the normal chair-like transition state. 

Phenolics and their functional derivatives are widely found throughout the plant kingdom. One defining characteristic of these compounds is that their aromatic ring usually contains at least one hydroxyl substituent. In a broad sense, phenolics, which are classified according to their structural skeleton, are basically derivatives from simple phenols and phenolic acids, phenylpropanoids including coumarins and lignans, flavonoids and related compounds, and stilbenes. Some of these compounds which show anti-inflammatory activity are reviewed in this section. 

Several experimental data supported that VOQ contains a higher concentration of three phenolic antioxidants classes, simple phenols, secoiridoids and lignans, and squaiene than RVO and seed oils. For these reasons, in the Mediterranean region, where olive oil is an essential constituent of the diet, there is a lower incidence of cancer and heart disease [63],... 

Even within the bryophytes, the simple 8,8 linked lignans (+)-megacerotonic and (+)-anthocerotonic acids, lacking regiospecific O-methylation at C3, have been identified in some hornworts (Anthocerotae). However, the lignans found in the Blechnaceous tree ferns, within the Pterydophytes, have 0-specific methylation and reductive modifications [2]. 

Another simple synthesis of lignans of the lariciresinol type (11) involves a straightforward reduction of a functionalised dibenzylbutyrolactone such as (75) or (76) followed by acid-catalysed cyclisation (scheme 24) [77,78]. Cyclisation of the doubly functionalised precursor (77) affords access to the furofuran skeleton (78) (scheme 25). A second synthesis which has also been extended to the furofuran series involves a radical cyclisation step, which proceeds with high stereoselectivity (scheme 26) [79]. This route has been used to synthesise (79) which is a precursor for the synthesis of sesamin and eudesmin [80]. 

Owen, R.W., Mier, W., Giacosa, A., Hull, W.E., Spiegelhalder, B., and Bartsch, H., Phenolic compounds and squalene in olive oils The concentration and antioxidant potential of total phenols, simple phenols, secoiridoids, lignans and squalene, Food Chem. Toxicol., 38, 647-659, 2000. 

In this chapter, the origin of cinnamic and p-coumaric acids and their simple derivatives will be discussed initially, as these intermediate substances are precursors to most other groups of related compounds. Various other modified C6-C3 compounds, such as simple phenylpropanoids, lignans, neolignans, lignin, and hydroxybenzoic acids, will then be covered. 

Nonflavonoid compounds comprise simple phenols, phenolic acids, coumarins, xanthones, stilbenes, lignins, and lignans. Phenolic acids are further divided into benzoic acid derivatives, based on a C6-C1 skeleton and cinnamic acid derivatives, which are based on a C6-C3 skeleton [6], The conmarins are phenolic acid derivatives composed of a benzene ring fnsed with an oxygen heterocycle. Xanthones consist of a C6-C1-C6 basic structure, and stilbenes are composed of a C6-C2-C6 skeleton with various hydroxylation patterns [13], Lignins are polymers of C6-C3 units, whereas lignans are made up of two phenylpropane units [13]. The structures of each of these classes are shown in Table 16.1. 

At the moment, such generalisations are without scientific foundation, but remain tempting when one examines lignans such as the justicidins and related compounds, which are simple arylnaphthalenes with no stereochemical complications (Fig. 8). The tests on these closely related compounds have been carried out in different laboratories mainly on the basis of folk medicine. 

Chapman s (O. L. Chapman, then at Iowa State and later at UCLA) classic total synthesis of ( )-carpanone is so remarkably simple that it is used as an imdergraduate laboratory preparation. It is modeled on a possible biosynthetic route for this lignan-derived natural product. Phenol oxidations figure prominently in many such bios)mtheses of natural products. In one step, this reaction creates no less than five contiguous chiral centers, all in the correct relative configuration. 

A straightforward classification attempts to divide the broad category of phenolics into simple phenols and polyphenols, based exclusively on the number of phenol subunits present, but many plant phenolic compounds are polymerized into larger molecules. Thus, the term plant phenolics encompasses simple phenols, phenolic acids, coumarins, flavonoids, stilbenes, hydrolyzable and condensed tannins, lignans, and hgnins [4]. 

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