Xanthene derivatives

Polymer supported xanthene derivatives have been used in the solid phase synthesis of 1-aminophosphinic acids, RCH(NH2)PH(0)0H, <%TL1647> and of C-terminal peptide amides <96JOC6326>. Xanthene units also feature in crown ethers <96JCS(P2)2091>, calixarenes <96JOC5670> and in a flexible template for a P-sheet nucleator <96JOC7408>. 

Chibale K, Visser M, van Schalkwyk D, Smith PJ, Saravanamuthu A, Fairlamb AH (2003) Exploring the potential of xanthene derivatives as trypanothione reductase inhibitors and chloroquine potentiating agents. Tetrahedron 59 2289-2296... 

Several xanthene derivatives are applied as acid dyes. For example, condensation of 3-diethylaminophenol with benzaldehyde-2,4-disulphonic acid, followed by cyclisation and oxidation, gives Acid Rhodamine B (6.197 Cl Acid Red 52). This dye is used in drop-on-demand ink-jet printing [36]. 

Xanthene dyes are used as colour formers. These so-called fluorans usually contain amino groups sited para and meta to the central carbon atom. Such a substitution pattern gives rise to broad absorption bands and leads to almost black colour production the lactone 6.200 is a typical example. This xanthene derivative finds use in direct thermal printing [36]. The chemistry of fluoran leuco dyes has been reviewed [78]. 

Various xanthene derivatives, including fluorescein, are also used as laser dyes to cover the spectral region from 500 to 700 nm. A modern example is the julolidine-based dye Rhodamine 101 (6.201), which absorbs at 576 nm and lases at 648 nm [79]. 

In this respect, Johansson 1 reported that ro is the same (within experimental accuracy) for fluorophores belonging to the same family, e.g. perylene and per-ylenyl compounds (0.369 + 0.002), or xanthene derivatives such as rhodamine... 

Double lithiation of the xanthene derivative 146 is the key step in an important synthesis of the ligand xantphos 147 Benzofuran 148 is also doubly lithiated by excess BuLi/TMEDA (Scheme 72) . 

Ma et al used TSIL [Rmim]HS04 to synthesize xanthene derivatives like 9-Aryl-3,4,5,6,7,9-hexahydroxanthene-l,8-dione. They also found that ILs such as [bmim][HS04] gave much higher yields of the product than [bmim][Br], [bmim][BF4] and [bmim][PF6]. The TSIL could easily be recovered and reused many times without any significant loss of activity. 

The anion derived from 2,3-dimethyl-l,4-naphthoquinone behaves as a quinone methide and undergoes a [l,4]-cycloaddition with the benzoquinone (193). The product is the xanthene derivative (194) (70JCS(C)722). There is no indication of the formation of the isomeric xanthene. A [l,3]-cycloaddition occurs simultaneously which leads to the fluorene derivative (195). 

Pyronines. Pyronines are diphenylmethane derivatives synthesized by the condensation of m-dialkylaminophenols with formaldehyde, followed by oxidation of the xanthene derivative to the corresponding xanthydrol. W hich in the presence of acid forms the dye (5). If R is methyl, the dye is pyronine G (Cl 45005) if R is ethyl, pyronine B (Cl 45010) is obtained. 

Arakawa et al.82) employed various 9-phenyl xanthene derivatives as the dye for DSC, and found that Eosin Y (EY Dye 18) shows relatively high conversion efficiency of 1.3% under 100 mW-cm"2 irradiance. They clarified the efficiency of 9-phenyl xanthene derivatives as follows EY > Dibromofluorescein > Fluorescein = Fluorescin > Rhodamin B > Dichlorofluorescein > Uranine >... 

In Section II.C we will present novel tricyclic xanthene derived amino acid templates, which allow the construction of libraries of cyclic conformationally constrained peptide loop mimetics using the split-and-mix method without having to use tagging and deconvolution strategies. In Section III we will focus on parallel and combinatorial approaches devoted to the synthesis of small molecule, non-peptidic compound collections, which in addition offer the possibility to incorporate structural features derived from protein epitope mapping into conformationally constrained peptide mimetics. 

Figure 27. Unsymmetrically substituted xanthene derived templates.

The reaction of indoles and pyrrole with pyrylium catalyzed by ceric ammonium nitrate in methanol furnishes the indole- and pyrrole-substituted xanthene derivatives in high yields <2007SL2222>. 

Intramolecular cyclisation following halogen-metal exchange in the benzonitrile derivatives 25 provides a route to xanthones and thioxanthones. Incorporation of a second aryl halide function into the benzonitrile substrate allows an anionic cascade ring-closing sequence and the formation of pentacyclic xanthene derivatives 26 <03JOC4091>. 

The anion derived from furobenzopyrandione 28 reacts with Michael acceptors regiospecifically to yield xanthones and various annulated derivatives <03OL3753> and intramolecular trapping of the anion by a carbamate side-chain leads to spiro- pyrrolidine and piperidine 9-xanthene derivatives <03TL9291>. 

The structure of the fluorescent sensor Fluo-3 consists of BAPTA attached to a xanthene derivative as the fluorophore (Fig. 18.2). Many xanthene-based (sometimes referred to fluorescein-based) fluorescent sensors such as Fluo-3 have been reported. These compounds have an aromatic moiety that recognizes or reacts with the target at the 9-position of the xanthene ring. 

The mechanism of the change of fluorescence intensity of xanthene-based fluorescent sensors was also studied, and it was hypothesized that photo-induced electron transfer between the xanthene and 9-aromatic moiety might be important. Nagano and Urano et al. systematically synthesized xanthene derivatives bearing various substituted phenyl groups at the 9-position, and confirmed that electron transfer has a significant role in their fluorescence properties they also showed that the determinants of electron transfer efficiency are physical parameters of the xanthene or... 

Dunayevskiy et al. showed the ability of HPCE-MS to determine the purity and composition of a library theoretically composed of 171 disubsti-tuted xanthene derivatives, with the possibility of analyzing libraries of up to 1000 components (92). Previously, the ability of MS alone to analyze a library of up to 55 components was shown (93), but it was suggested that for more... 

Figure 10 CE-MS electropherogram of different mixtures of xanthene derivatives in Tris-acetate buffer at pH 7.9. (a) Mixture 2, Ile/X/Ile(l), Ile/X/Pro (2), Ile/X/Ala (3), Pro/X/Pro (4), Pro/X/Ala (5), and Ala/X/Ala (6). (b) Mixture 2 dissolved in 20 mM Tris-acetate buffer at pH 7.9 containing 40% (vol/vol) MeOH. E + 07 = 107 (92). (Reproduced with permission of the copyright holder, publisher and the Proceedings of the National Academy of Science USA).

Inspired by the rapidly emerging model systems of artificial life [40], we were confronted with the question of whether synthetic replicators shuffle their components to generate new hybrid replicators. To answer this, we made use of a self-replicating system developed at the same time as the adenine biphenyl replicator, but which had never been fully explored. The replicator, pictured at the top of Figure 25, was based on molecular recognition of thymine derivative (41) and xanthene derivative (40) by template (42). Coupling of the... 

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