Bis-xanthones

Ondeyka JG, Dombrowski AW, Polishook JP, Felcetto T, Shoop WL, Guan Z, Singh SB (2006) Isolation and Insecticidal/Anthelmintic Activity of Xanthonol, a Novel Bis-Xanthone, from a Non-Sporulating Fungal Species. J Antibiot 59 288... 

Kelly JX, Winter R, Peyton DH, Hinrichs DJ, Riscoe M. (2002) Optimization of xanthones for antimalarial activity The 3,6-bis-co-diethylaminoalkoxyxanthone series. Antimicrob Agents Chemother 46 144-150. 

The key intermediate in the total synthesis of furaquinocin was obtained in good yield by a reductive Heck reaction that proceeded with a sterically hindered base pentamethylpiperidine (PMP) <02JA11616>. A new hypothesis for the major skeletal rearrangement (anthraquinone —> xanthone —> coumarin) that occurs in the complex biosynthesis of aflatoxin Bi was proposed. To test this hypothesis, an intermediate 11-hydroxy-O-methylstergmatocystin (HOMST) was synthesized as shown below. The key transformation in this synthesis involved the treatment of an ester-aldehyde with Pr3SiOTf, which smoothly produced a mixed acetal. Direct reduction with DIBAL-H led to the aldehyde. The desired product was eventually obtained via several steps as shown <02JA5294>. 

Fig. 1. Chemical structure of aflatoxins. (a) The B-type aflatoxins are characterized hy a cyclopeutane E-ring. These compoimds have a hlue fluorescence under long-wavelength ultraviolet hght (h) The G-type aflatoxins have a xanthone ring in place of the cyclopentane, (c) Aflatoxins of the B2 and G2 type have a saturated bis-furanyl ring. Only the bis-firran is shown, (d) Aflatoxins of the Bi and Gi type have a hydrated his-furanyl structure.

Sensitization and quenching of the intramolecular els -> trans isomerization of bis(glycinato)platlnum(II) has been investigated (226). Pyrazine (Ef = 74.9 kcal/mol) and xanthone (E.j = 74.3 kcal/mol) are effective sensitizers, producing the limiting quantum yields = 0.03 and = 0.1, respectively. With... 

Bis(2-diethylaminoethoxy) fluoren-9-one or tilorone dihydrochloride and related compounds e.g. - fluorenone ethers - fluorenone esters - fluorene ketones - fluorenone ketones - dibenzofuran ketones - xanthone ethers - anthraquinone ethers - anthraquinone sulfonamides - fluoranthene esters 2. Thiazine and acridine derivatives - Thiazine derivatives in vivo (mice, rats) Late 85-91)... 

Dichlor-xanthon reagiert bei Verschmelzen mit Kupfer-Pulvcr zu 4,4 -Dichlor-1,1 -bi-xanthonyl2 (F>290°) ... 

Isomerization of the anion 46, analogous to a DiMROTH rearrangement (see p 202), is assumed to be the key step in this reaction. An application of this reaction principle is to be found in the synthesis of xanthone 49, which is effected by a base-catalysed isomerization of the bis-2//-pyran-2-one 48 ... 

Successive treatment of bis-3,3-dimethylallenyl sulphone (357) with butyl-lithium in THF at 0 °C gave a 60% yield of the dithia-adamantane (358), whose structure was confirmed by X-ray crystallography. Photolysis of thietans in the presence of a new triplet sensitizer, l,3-dimethyl-2-thioxoimidazolidine-4,5-dione, has produced interesting results for example, the spiro-xanthone (359) gave the acetate (360), but in u.v. light, and without the sensitizer, the thiopyran (361) was obtained in addition to (360). Among several flavonoids identified in a Chinese plant. Euphorbia lunulata Bge., which is used in the treatment of... 

BiosyntheticaUy, the aflatoxins are all formed from the same precursor, versiconal hemiacetal acetate (12) (25). Compound 12 is formed from acetate, the units of which are converted into a polyketide. The polyketide is then metabolized to the xanthone 12 (see Scheme 2.1) (26). Intermediate 12 can then be transformed either into versicolorin A (13) or versicolorin B (14) in several steps. Versicolorin A (13) may be converted to sterigmatocystin (15), while 14 can lead to dihydro-sterigmatocystin (16). Sterigmatocystin (15) can be metabolized to aflatoxins Gi (3) or Bi (1) and the latter may then be transformed to aflatoxin Mi (5). Aflatoxins B2 (2) and G2 (4) are formed from dihydrosterigmatocystin (16) and aflatoxin M2 (6) is formed by conversion from B2 (2). Pathways also exist to convert aflatoxin Bi (1) to B2 (2), Ml (5) to M2 (6), and Gj (3) to G2 (4), and vice versa. Important biosynthesis steps are shown in Scheme 2.1. 

The fungal metabolite aflatoxin Bi (31) is derived from a cooccurring xanthone sterigmatocystin (32) which is, in turn, produced by oxidative cleavage of the anthraquinone versi-colorin A (28) (Fig. 5.17). Aflatoxins are among the most... 

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