Juglone derivative

The importance of both electronic and steric effects is clear in cycloadditions as in cross-oxidations. One example is a heterocycHc modification leading to the thermodynamically less stable natural form of juglone derivatives such as ventiloquinones JT [124917-64-2] (84) and I [124917-65-3] (85) (83). The yields are 97% (84) from 6-chloro-2,3-dimethoxy-l,4-ben2oquinone [30839-34-0] and 100% (85) upon hydrolysis. 

Judd-Hunter color difference scale, 7 321 Juglone, in skin coloring products, 7 847 Juglone derivatives, 21 264-265 Juice softening, 23 463 Junctional heart rhythm, 5 107 Junction capacitance, 22 244 Junction devices, 22 180-181 Junction FETs (JFETs), 22 163, 164. See also Field effect transistors (FETs) physics of, 22 241-245, 249 Junction potentials, 9 582 Junctions, stacking, 23 38-39. See also Josephson junctions p-n junction Just-in-Time technique, 21 172 Jute, 11 287, 288, 292, 293. See also China jute... 

Some naturally occurring prenylated juglone derivatives have been synthesized from 2,8-dihydroxy-1,4-naphthoquinone as it is illustrated in Fig. (20) [156],... 

In nature, the oxidative dimerization of phenols is controlled by enzymes, as is demonstrated by the axial chirality of the 6,8 -coupled juglone derivative isodiospyrin. In synthesis, however, phenol oxidation only proceeds in high yields when the enzymatic reaction control is replaced by substituent control, that is, if all but one of the positions with high spin density in the radical (ortho-and para positions) are blocked. 

Diels-AUer reactions. The diene reacts with the juglone derivative 2 to give, after pyrolysis and desilylation, the anthraquinone 3. Other regiospecffic cycloadditions are reported. 

Figure 6.12. Degradation of juglone derived from isotopically labelled (—)-...

Derivatives of the natural product juglone [77189-69-6] eg (109), have been obtained ia 90% yield ia a single reaction involving halogenation and oxidation by A/-bromosucciniinide (115). 

The synthesis of the naphthoquinone 116 is shown in Scheme 3.24. Bromination of juglone (118) afforded the dibromojuglone derivative 134. Protection of the phenol group as its methoxymethyl ether formed the product 135 (50 % yield over two steps). Finally, the C-3 bromide substituent was regioselectively substituted with methoxide by heating 135 in methanol in the presence of sodium carbonate (96 %). The methoxy group was installed to impart electronic bias to the naphthoquinone in the TASF(Et) coupling (vide infra). 

It seems unlikely that the allelopathic chemicals that may be extracted from plant material are actually those that reach the host plant, yet nearly all our information on allelopathic compounds is derived from extracts that have never been exposed to the soil. Some compounds, such as juglone, may remain unchanged in the soil under some circumstances ( ), but many compounds, such as ferulic or salicylic acid, are converted to other chemicals in the soil. 

This enzyme exhibits no hydroxylase activity and is involved in the final synthesis of many naturally occurring /t-quinoncs. e.g. the naphthaquinone juglone in walnut (1.58) and the benzoquinone arbutin (hydroquinone-(3-D-glucopyranoside 2.46). Arbutin is a plant cryo-protectant that stabilizes membranes (Hincha et al., 1999). This compound has medicinal properties and has, for example, been used to treat urinary tract infections in humans. It is also used to lighten skin color, because it inhibits tyrosinase and hence the formation of melanin. The derivative deoxyarbutin (2.47 note the difference in the sugar molecule) was recently reported to be considerably more effective as a skin-lightening compound (Boissy et al., 2005). 

Chiral borane reagents similar to those described above were independently reported by Yamamoto and co-workers in the same year (Eq. 2) [2]. These reagents promote the reaction of juglone and a variety of dienes in the synthesis of anthracycli-nones. The borane reagent used is trimethyl borate. Different tartrate derivatives have been tried and (i ,f )-(+)-tartaric acid diamide has proved to be the most efficient. The best results are obtained in the reaction of juglone and (triethylsiloxy)buta-... 

Although the X-ray structure of a Pinl-dipeptide complex implicated covalent catalysis, a lack of nucleophilic assistance in the catalytic pathway can be derived from the covalent modification of parvulins by 5-OH-l,4-naphthoquinone (juglone). A juglone-inactivated E. coli ParlO contains two inhibitor molecules that are covalently bound to the side-chains of Cys41 and Cys69 because of a Michael... 

The naphthalene derivatives (171, 172), from Daldinia concentrica (Ascomycetes), were significantly active towards C. elegans (10, 25 (ig/ml) and also showed antimicrobial and cytotoxic activity [6]. Since the black fruiting bodies of D. concentrica are highly melanized, it is likely that these compounds arise from melanin biosynthesis. Some naphthoquinones have been found to inhibit the motility and survival of H. contortus (LI). Plumbagin ( 173) was the most potent (ED 1 ig/ml) followed by 1, 4-naphthoquinone, juglone (174) and 1, 2-naphthoquinone [281]. 

The biosynthesis of these anthraquinones parallels those of the menoquinones in bacteria and naphtoquinones of plants for example juglone, vitamin K and lawsone. These compounds are also derived from shikimic (or chorismic) and a-ketoglutaric acids via o-succinylbenzoic acid [5,24]. 1,4-Dihydroxy-2-naphtoic acid is the branching point in the biosynthesis of menoquinones, naphtoquinones and anthraquinones [4],... 

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