Oxygen heterocycles compounds

P Dugo, L. Mondello, E. Sebastian , R. Ottana, G. Eirante and G. Dugo, Identification of minor oxygen heterocyclic compounds of citi us essential oils by liquid chromatography-atmospheric pressure chemical ionisation mass specti ometiy , J. Liq. Chromatogr. 22 2991-3005 (1999). 

The distribution of oxygen heterocyclic compounds differs in Robusta and Arabica roasted coffees some concentration values are given in Table 9.39 Roasted Robusta contains relatively high proportions of furfuryl alcohol and the caramel flavored maltol (Figure 7) in comparison with roasted Arabica.39... 

Girgis, M. J., and Gates, B. C., Catalytic Hydroprocessing of Simulated Heavy Coal Liquids. 2. Reaction Networks of Aromatic Hydrocarbons and Sulfur and Oxygen Heterocyclic Compounds. Ind. Eng. Chem. Res, 1994. 33 pp. 2301-2313. 

A variety of names has been used for the benzologues of pyran and its derivatives, many of which have been described in two treatises on oxygen heterocyclic compounds <77HC(3l)l, 81HC(36)l). It is of value to indicate the nomenclature which has been adopted in this and the two following chapters, since it is not always considered appropriate to use the more cumbersome and less familiar systematic names. 

The presence of a six-membered oxygen heterocyclic ring in a range of naturally occurring compounds provided the stimulus for the development of synthetic routes to these compounds. Many of the methods which evolved in the closing years of the 19th century and the earlier decades of this century are still of value today. These routes have been supplemented by modern approaches and consequently there is often a choice of methods available for the synthesis of a particular oxygen heterocyclic compound. 

In general, the synthetic routes described provide adequate and convenient routes to chromones, such that their synthesis from other oxygen heterocyclic compounds is not of significant value. The following examples are therefore better considered as reactions of the heterocycle and are dealt with in more detail in the appropriate sections of Chapter 2.23. 

Dugo, P., Mondello, L., Dugo, L., Gugo, L., Stancanelli, R., and Dugo, G. (2000). LC-MS for the identification of oxygen heterocyclic compounds in citrus essential oils. J. Pharm. Biomed. Anal. 24,... 

Six-membered unsaturated oxygen heterocyclic compounds are based on three molecules 2/7-pyran 1,4/7-pyran 2, and the pyrylium ion 3. Based on this, the benzo analog of 2/7-pyran is named 277-1-benzopyran (commonly 2H-chromene) and the benzo analog of 477-pyran is called 4/7-1-benzopyran (commonly 477-chromene). The benzo analog of 3 is known as 1-benzopyrylium 6 (sometimes chromylium). Related naphthyl analogs are exemplified by 2/7-naphtho[l,2,A]pyran 7, the xanthylium ion 8, and xanthene 9. 

A number of other rather unusual reactions have, however, been observed during the degradation of oxygen heterocyclic compounds and these are worth illustrating ... 

Table III lists some of the compounds which have been identified in these fractions which are mainly mono phenolic types and oxygenated heterocyclic compounds. All the chromatograms of F3 to FIO showed well resolved peaks but Fll suffered from peak broadening which is more likely due to the contamination from F12. Examples of a few chromatograms are presented in Fig. 3 and are compared with a chromatogram of the total oil from H-VI (Fig. 3a). From Fig. 3a, we could only identify a few compounds and the rest...

The oxygen heterocyclic compounds present in the nonvolatile residue of citrus essential oils have also been extensively investigated by means of HPLC-atmospheric pressure ionization-mass spectrometry (HPLC-API-MS) [99]. The mass spectra obtained at different voltages of the sample cone have been used to build a library. Citrus essential oils have been analyzed with this system, using an optimized NP-HPLC method, and the mass spectra were compared with those of the laboratory-constructed library. This approach allowed the rapid identi cation and characterization of oxygen heterocyclic compounds of citrus oils, the detection of some minor components for the rst time in some oils, and also the detection of authenticity and possible adulteration. 

Dugo, P L. Mondello, E. Cogliro, A. Verzera, and G. Dugo, 1996. On the genuineness of citrus essential oils. 51. Oxygen heterocyclic compounds of bitter orange oil Citrus aurantium L.). 

McHale, D. and J.B. Sheridan, 1989. The oxygen heterocyclic compounds of citrus peel oils,... 

Some natural complex matrices do not need sample preparation prior to GC analysis, for example, essential oils. The latter generally contain only volatile components, since their preparation is performed by SD. Citrus oils, extracted by cold-pressing machines, are an exception, containing more than 200 volatile and nonvolatile components. The volatile fraction represents 90-99% of the entire oil, and is represented by mono- and sesquiterpene hydrocarbons and their oxygenated derivatives, along with aliphatic aldehydes, alcohols, and esters the nonvolatile fraction, constituting 1-10% of the oil, is represented mainly by hydrocarbons, fatty acids, sterols, carotenoids, waxes, and oxygen heterocyclic compounds (coumarins, psoralens, and polymethoxylated flavones—PMFs) [92]. 

Figure 8 presents a selected part of a gas chromatogram recorded for the extracts A and B. The extract B consisting of furan derivative contains more oxygen heterocyclic compounds compared to extract A. The excess of 0-heterocycles is responsible for the observed (better) antioxidant activity of extract B (Figure 9). Careful analysis of GC, FT-IR, and NMR results let to identify more than 50 compounds which conld be accounted to the compounds potentially exhibiting antioxidant activity. Some of them are listed in Table 3 which contains names, formulas and information on most typical MS ions observed during the GC-MS identification. In general, most of the identified compounds may be seen as derivatives of the three basic structures (Figure 10) (A) cumarol alcohol, (B) coniferyl alcohol, and (C) synapine alcohol.

Scheline RR. Metabohsm of oxygen heterocyclic compounds. In CRC Handbook of mammalian metabohsm of plant compounds. Boca Raton, FL CRC Press,... 

---