1,3-Diketone moiety

IR spectra of PAN obtained from the CAN-1,3-diketone systems revealed that, besides the characteristic absorption band of CN group at 2244 cm , the characteristic absorption bands at 1727 and 1700 cm (keto form of 1,3-diketone) and 1625 cm (enol form of 1,3-diketone) were observed simultaneously. Therefore, the 1,3-diketone moiety is present as an end group in PAN. 

Depending on the substitution pattern in the amidrazonium and 1,3-diketone moieties, 1,3-diketone monobenz- or monoacetamidrazonium salts (86ZOR500) may exist exclusively as the open-chain isomer 59A-Z (R1 = R3 = H R2 = Ph R4 = Me R5 = CMe2COMe) or exclusively as the cyclic isomers 59B (R1 = H R2 = Ph R3 = R4 = Me R5 = CH2COMe) or they may exist as a tautomeric mixture containing not only 59A-Z, but also the enhydrazine-like open-chain tautomer and the cyclic pyrazoline tautomer formed by intramolecular N(2) —H group (R3 = H) addition to the second C=0 group of the 1,3-diketone. 

Chebanov and co-workers [130] described an efficient synthetic route for the synthesis of some novel derivatives of 5a-hydroxy-4,5,5a,6,7,8-hexahydropyra-zolo[4,3-c]quinolizin-9-ones 94 which is based on a multicomponent condensation of a 5-aminopyrazole with a cyclic 1,3-diketone and an aromatic aldehyde under microwave irradiation. The reaction runs via an unusual base-mediated ring-opening/recyclization of the cyclic 1,3-diketone moiety (Scheme 71)... 

From the rhizomes of C. longa, several curcuminoids (237-240) [191], (245,246) [192] and two curcumin related phenolic compounds (247,248) [191] were isolated. Antioxidant activity of the two phenolic compounds 247 and 248 was determined by inhibiting the autooxidation of linoleic acid and comparing the activity with that of curcumin [191]. Compounds 247 and 248 showed stronger activity than that of curcumin. It seems to indicate that the chelation of the 1,3-diketone moiety is not so important... 

Potent HPPD inhibitors have a common structural feature in the form of a 1,3-diketone moiety (9, 10, II). Kinetics experiments show that these potent inhibitors exhibit the characteristics of slow-tight binding inhibitors (12, 13, 14, IS). Figure 2 contains examples of various structural classes of inhibitors all with the 1,3-diketone motif. Mesotrione and the diketonitrile form of... 

Typical biodegradants - oxidase and dehydrogenase give p-hydroxylketone as well as 1,3-diketone moieties ... 

In recent years, there has been a considerable effort to expand the range of iodonium salts that can be employed as photoinitiators for cationic polymerizations. Stable iodonium salts can be obtained when one of the aryl groups in 51 is replaced by a moiety that can provide resonance stabilization to the positively charged iodine atom. For example, Koser et prepared stable aryl (phenyl ethynyl)iodonium salts, 55, that were shown by Kitamura et al. and by Hofer and Liska to exhibit good activity as cationic photoinitiators. Similarly, iodonium salts, 56, in which the positively charged iodine atom is attached to the central carbon of a resonance-stabilized 1,3-diketone moiety such as dimedone are also isolable compounds that display the ability to serve as photoinitiators for cationic polymerization. Finally, it has been reported that diaryl(oxo)iodonium salts, 57, can be readily prepared by the base-catalyzed self-condensation of diaryliodyl compounds. Replacement of the initial... 

OS 52] [R 4b] [P 38] See discussions in the preceding and following sections [8]. Reactivity of different substrates with diketone moieties... 

OS 52[ [OS 53[ [OS 54[ [OS 55[ [R 4b[ [P 38[ In a two-micro-mixing tee chip reactor, substrates with diketone moieties of known different reactivity, such as 2,4-pentanedione, benzoylacetone and diethyl malonate, were processed, each with the same acceptor ethyl propiolate [8]. Also, a reaction with the less alkynic Michael acceptor methyl vinyl ketone was carried out. 

Fig. 5 Enzymatic oxidation of highly hydrolysed PVA proceeds in two steps 1,3-diol elements in PVA are oxidised via the [l-OH-ketone to form a diketone moiety. Three enzyme systems using different electron acceptors as cofactors/cosubstrates are shown...

The a, p-unsaturated diketone moiety in the curcuminoids is a Michael reaction acceptor, which belongs to the major class of phase II enzyme inducers... 

Further studies are required to unravel this mystery of how the methoxy substitutions and the a, p-unsaturated p-diketone moiety actually influence conformational changes, lipophillicity, electron density distribution, and redox properties of curcuminoids. Correlating these physicochemical properties with the unique pleiotropic effects of curcuminoids is a rewarding exercise. Such studies would definitely provide proper reasoning in understanding these markedly different antioxidant, antitumor, and anti-inflammatory activities of natural curcuminoids from turmeric. 

Cyclocurcumin differs from curcumin in the p-diketone link. In this molecule, the a, p-unsaturated p-diketone moiety of curcumin is replaced by a, p-unsaturated dihydropyranone moiety. Up to now, not many biological studies are reported with cyclocurcumin except for one study on inhibition of MCF-7 tumor cell proliferation by Simon et al. [1998] where it has been found to be ineffective in inhibiting cell proliferation and arrest of cell-cycle progression. 

The quaternary carbon at C 12a separates the chromophores of the tetracyclines into two relatively distinct regions. The B-tricarbo-nyl system of ring A contributes a strong absorption band at about 260 nm while the aromatic ring D conjugates with the B-diketone moiety in rings B and C to produce a visible band at about 360 nm (21). the molecular extinction coefficients and Alj of TC-HC1 in different solvents are reported to be (22) ... 

In a straightforward refinement of their concept Rubin et al. have turned to cyclophyne 14 [32] in which the vinylic hydrogens of 13 are replaced by 1,2-dioxocyclobuteno groups. This cyclic diketone moiety has been used previously [18, 33, 34] as a synthetic equivalent for alkynyl groups which can be generated from the dione by thermally or photochemically induced CO expulsion. Successive decarbonylation of 14 should ultimately lead to cyclophyne 15 with the composition Q0H6. 

Other nucleophiles such as trimethylsilyl azide or trimethylsilyl acetate reacted in the same way and the azido or acetoxy group was similarly introduced to the aromatic substrate. Phenol ethers incorporating a /i-diketonic moiety at the metaposition underwent an analogous intramolecular aromatic alkylation [24] ... 

Stable metal complexes can be favorably formed when a bidentate metal-binding site is available, such as a- and -diketone moieties which are the tautomeric forms of a- and /3-ketoenols. Some /S-diketonate complexes of paramagnetic lanthanides such as Pr(III), Eu(III) and Yb(III) have been extensively utilized as paramagnetic shift reagents for structural assignment of molecules with complicated stereochemistry prior to 2D techniques in NMR spectroscopy. Their syntheses and application are discussed in separate chapters in this volume. The examples below provide some dynamic and structural basis for better understanding of metal enolates in biomolecules and biochemical processes. 

The /3-diketone moiety in conjugation with the phenolic groups contributes greatly to the anti-inflammatory and anti-tumor activity of curcumin/ The rate constants for the reactions of several oxidizing free radicals with quercetin and curcumin are given in Table 2. 

A particularly interesting copper-barium-2-methoxyethoxide derivative, Ba2Cu2(OC2H40Me)4(acac)4 2HOC2H4OMe, was recently (386) isolated from the reaction of (acac)Cu(OC2H4OMe) with Ba(OC2H4OMe)2. The solid state structure is shown in Fig. 61 and indicates that a /3-diketonate moiety was transferred from the copper center to barium. 

Recently, another antioxidant mechanism was proposed for cnrcnmin which involved an initial carbon-centered radical at the -diketone moiety that snbsequently nndergoes rapid intramolecnlar hydrogen shift to a phenoxyl radical . Obvionsly, this mechanism does not acconnt for the antioxidant activity results with peroxyl radicals . 

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