The furan ring can be replaced by a
pyran one maintaining a good inhibition of IL-8 expression ("
pyran series" 35-36).
Also, it can be observed signals for the carbons of the two rings inserted in the xanthone basic structure: signals for three methyl groups: 18.7 and 27.4 ppm for those connected to the
pyran ring, and 23.6 ppm for the methyl group attached to the [sp.sup.2] carbon; two methylene groups, at 27.7 and 36.8 ppm; two methyne groups, at approximately 31.0 and 44.4 ppm, and a signal to a tetrasubstituted carbon at 78.5 ppm.
The polyphenolic flavonoids share a basic 15-carbon skeleton core structure (represented as C6-C3-C6) consisting of two phenylbenzene (chromanol) rings linked through a
pyran ring.
Flavonoids contain two phenolic moieties and a
pyran unit [1].
This observation was not immediately apparent because
pyran copolymers are well-known antiviral agents [203].
Abdel-Rahman, "Antimicrobial activity of new 4,6-disubstituted pyrimidine, pyrazoline, and
pyran derivatives," Archives of Pharmacal Research, vol.
Khan, "One-pot three-component reaction for the synthesis of
pyran annulated heterocyclic compounds using DMAP as a catalyst," Tetrahedron Letters, vol.
The theoretical and experimental studies of
pyran dyes have been extensively investigated [30-33].
Their structure is characterized by a three carbon chain (C6-C3-C6) system joined together by two phenyl rings, where C3 is an aliphatic chain and two C6 groups are substituted benzene rings containing a
pyran ring (Fig.
Forming a six membered ring sugar termed a pyranose; a derivative from a heterocyclic compound
pyran. Pyranoses are formed by the reaction between an alcohol and an aldehyde forming a hemiacetal.