Secondary metabolites characterization

The occurrence in some plants of secondary metabolites characterized by an 0-heterocyclic structure and exhibiting antimicrobial properties is a well-known phenomenon [2,8-10]. Among them, catechins and proanthocyanidins are two classes of compounds exhibiting antimicrobial properties towards both prokaryotic and eukaryotic microorganisms. Yet, despite the large number of studies published so far, the real potentialities and limitations given by the use of this class of molecules as antiviral or antimicrobial (antibacterial, antimycotic, antiprotozoal) agents have not been critically evaluated. The present chapter represents an overview of the re-... 

Chemically, limonoids are unique secondary metabolites, characterized by a tetranortriterpenoid skeleton with a furan ring (Fig. 1.8). They are commonly isolated from Citrous and Maliaceae plants (Hallur et al. 2002 Rahman et al. 2009 Vikram et al. 2010). Besides their health promoting effects, various limonoids have been shown to possess antibacterial, antifungal and antiviral effects (Govindachari et al. 2000 BattineUi et al. 2003 Atawodi and Atawodi 2009). 

Intact bacteria were first introduced into a mass spectrometer for analysis of molecular biomarkers without processing and fractionation around 1975.6 The ionization techniques available at the time limited analysis to secondary metabolites that could be volatilized, such as quinines and diglycerides, and vigorous pyrolysis of bacteria was explored as an alternative.7 Although biomarkers were destroyed in pyrolysis strategies, computer-supported cluster analysis was developed to characterize pure samples. 

Pulmonates are air-breathing molluscs that do not include many families and genera [68]. Siphonaria species from many distinct geographical areas possess a series of secondary metabolites with polypropionate skeletons characterized by the presence of ketal, pyrone and furanone moieties [47]. A rigorous biosynthetic experiment [69] proved that Siphonaria denticulata is able to... 

DMSP is a compound that cannot easily be characterized as either a primary or a secondary metabolite because it has primary functions in some organisms and secondary functions in others (Stefels 2000 Steinke et al. 2002 Yoch 2002) in many, if not most of the organisms that produce it, it probably has both. In addition to their physiological and ecological roles, DMSP and DMS are important to global biogeochemical cycling and possibly climate (Malin et al. 1992 Liss et al. 1994 Malin and Kirst 1997 Yoch 2002). 

The 4-coumarate CoA ligase (4CL EC 6.2.1.12) enzyme activates 4-coumaric acid, caffeic acid, ferrulic acid, and (in some cases) sinapic acid by the formation of CoA esters that serve as branch-point metabolites between the phenylpropanoid pathway and the synthesis of secondary metabolites [46, 47]. The reaction has an absolute requirement for Mg " and ATP as cofactors. Multiple isozymes are present in all plants where it has been studied, some of which have variable substrate specificities consistent with a potential role in controlling accumulation of secondary metabolite end-products. Examination of a navel orange EST database (CitEST) for flavonoid biosynthetic genes resulted in the identification of 10 tentative consensus sequences that potentially represent a multi-enzyme family [29]. Eurther biochemical characterization will be necessary to establish whether these genes have 4CL activity and, if so, whether preferential substrate usage is observed. 

NMR, UV and IR spectroscopies are routinely used for the characterization of the majority of reviewed systems and the reader is referred to the individual references for this information. The special cases of structure elucidation of a secondary metabolite of the Chinese drug Danshen Salvia miltiorrhiza Bunge) by... 

Antibiotics are generally defined as low molecular mass microbial secondary metabolites which, at low concentrations, inhibit the growth of other microorganisms. To date, well in excess of 10 000 antibiotic substances have been isolated and characterized. Overall, antibiotics are a chemically heterogeneous group of molecules, although (as described later) many can be classified into different families based upon similarity of chemical structure. 

Metabolic transformations are characterized by high speed and yield, as well as high regio-, diastereo-and enantio-specificity. Errors in the stereochemistry of the molecules that serve to construct the genetic material are smaller than for the planetary motions. With secondary metabolites, however, enantiomerically inq)ure con unds are also encoimtered, typkally with monoterpenes and alkaloids from terrestrial plants even ant dal pathways in the same organism have been found, albeit as rare events (Guella 1998). 

Saleem M, Akhtar N, Riaz N, Ali MS, Jabbar A. Isolation and Characterization of Secondary Metabolites from Plumeria obtusa. Journal of Asian Natural Products Research 2011 13(12) 1122-1127. 

Phytochemical studies of these species led to the isolation and structural characterization, by NMR and MS analysis, of many secondary metabolites, mainly flavonoids, and expecially flavonol glycosides, clerodane diterpenes, and triterpenes having the lupane, ursane, and oleanane skeletons. Particularly flavonoids and their glycosides have a chemotaxonomic interest in the genus and in general in the Chrysobalanaceae family. 

In the course of our phytochemical work we studied seven Licania species all belonging to Venezuelan flora, collected in Puerto Ayacucho, Estado Amazonas and in the Parque Nacional Henry Pittieri, Maracay, Estado Aragua. A number of new and known secondary metabolites, mainly flavonoids, especially flavonol glycosides, sterols, and triterpenes having the lupane, ursane, and oleanane skeleton were isolated and characterized. The last part of this chapter deals also with the isolation of clerodane diterpenes from the methanol extract of L. intrapetiolaris by Oberlies et al., 2001 [4]. All the Licania species investigated up to now are reported in Table 1. 

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