Prenyl substituents

Benzophenones and xanthones have the C6-C1-C6 structure. The basic structure of benzophenone is a diphenyl ketone, and that of xanthone is a lO-oxy-10/7-9-oxaanthracene. More than 500 xanthones are currently known to exist in nature, and approximately 50 of them are found in the mangosteen with prenyl substituents. 

Some of the compounds listed in Table 15.3 not only bear prenyl substituents, but also C-methyl or related groups, e.g., flavanone 50 from Dalea caerulea (Leguminosae), the regioisomers 53 and 54 from Eysenhardtia texana (Leguminosae), and the regioisomers... 

Losses of small molecules and/or radicals from [M+H]" are observed in the positive-ion mode losses of HjO, CO, and HjC=C=0, and combinations thereof. The loss of a methyl radical CHj is characteristic for O-methylated isoflavones, flavones, and flavonols [13]. Loss of C4H8 indicates the presence of prenyl substituents (at 3-, 6-, and/or 8-position) [t4]. Kuhn et al. [t5] demonstrated the differentiation between isomeric flavones and isoflavones by means of positive-ion MS-MS in an ion-trap instmment. tsoflavones show an abundant fragment ion due to the loss of 2 CO molecules from the C-ring, while flavones only show a single CO loss. 

In this group, some compounds are prenylated, such as dimethyl-moracin I (88), artoindonesianin O (103), 3-(, -dimethylpro-penyl)moracin M (106) and flavescenone C (109). Lakoochin A (89) possesses two prenyl groups, while lakoochin B (90) has a prenyl substituent at C-2 and a geranyl substituent at C-6. Another new benzofuran derivative macrourin A (107) from the barks of Morns macroura Miq., is identified as both prenylated and geranylated with a chromene partial structure [58], Fig. 

MK biosynthesis by the OSB pathway has been elucidated on the basis of isotopic tracer experiments, isolation of mutants blocked in the various steps, isolation and identification of intermediates accumulated by the mutants, and by enzyme assays. Early isotopic tracer experiments with various bacteria established that methionine and prenyl PPi contribute to the methyl and prenyl substituents of the naphthoquinone. The early isotopic tracer studies and other work have been reviewed by Bentley and Meganathan. " In 1964, Cox and Gibson observed that [G- " C] shikimate was incorporated into both MK and ubiquinone by E. coli, thus providing the first evidence for the involvement of the shikimate pathway." Chemical degradation of the labeled isolated menaquinone (MK-8) showed that essentially all of the radioactivity was retained in the phthalic anhydride. It was concluded that the benzene ring of the naphthoquinone (sic) portion of vitamin K2 arises from shikimate in E. coli The authors further suggested that shikimate was first converted to chorismate before incorporation into MK. A more complete chemical degradation of the MK derived from... 

Prenylquinoline Alkaloids.—This group includes those alkaloids derived notion-ally by cyclization of a 3-prenyl substituent. This process was used to synthesize the pyranoquinolone alkaloid, haplamine (18), which was formed by reaction of the... 

Danishefsky and coworkers developed a method for introducing the tcrt-prenyl group at the indole C-2 position based on C-3 chlorination followed by nucleophilic delivery of the ferf-prenyl group from a borane [99]. The intermediate was used in synthesis of gypsetin and breviamide E, both of which contain the 2-(tert-prenyl) substituent. 

IMoracln(s). A group of phytoalexins from the mulberry tree (Monts alba). They are formed after infection of the tree with the fungus Fusarium solani. All 26 of the currently known M. (M. A to Z) have the 2-phenylbenzofuran skeleton bearing hydroxy, methoxy, and prenyl substituents. 

Scheme 22. Possible mechanism for introduction of the reverse prenyl substituent [44]...

According to the structure, pterocarpans are divided into simple pterocarpans (an example is medicarpin with a methoxyl group and maackiain with a methylenedioxy group), pterocarpans (such as coumestrol) and 6-hydroxypterocarpans (such as pisatin), some of which, such as glyceollin III (10-103) with a prenylated substituent on the furan ring, have a more complex structure. 

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