Benzopyran moiety

Classical cannabinoids (CCs) are tricyclic terpenoid derivatives bearing a benzopyran moiety. This class includes the natural product (-)-delta-nine-tetrahydrocannabinol (Fig. 8, 1) and the other pharmacologically active constituents of the plant Cannabis sativa. 

As to the third step of the step-wise one-electron reduction of t//-nilro-spiro(indoline-benzopyran), the third extra electron is again accommodated into the nitrobenzopyran unit without affecting the spin density distribution on the opposite fragment, which therefore remains essentially identical to that of the anion radical of mono-nitro-spiro(indoline-ben-zopyran). Hence, the spiro-nodal carbon atom prevents conjugate interactions between the indoline and benzopyran moieties. 

Ab initio calculations at the ROHF/3-21G level were carried out for the radical anions from compounds 57, 58 and 65 as well as for the dianions and trianions from 65 in order to check whether the formation of the trianions is energetically feasible. The results indicated that the unpaired electron in the naked 65 radical anion is preferentially located on the benzopyranic moiety ( =0) rather than on the indolinic unit (E=0.33 eV) and that the radical trianion would be characterized by a forbiddingly high energy (E = 8.6 eV). 

These structural features lead to different orientations of the 7t-electron density of the O-atom LEP and the Cspjro—N(l ) bond (angle A, Table 1). In SP2, SP3, SP4b, SP6, and SP7, the corresponding angle is only 116-130° in SP4a and SP9-SP11, it is 141-145° and in SPS and in SP1, it is 160.2° Thus, the k(0) a [Cspiro—N(l )] interaction, which has an opposite effect to the nlNOOl-o Cspiro-O) interaction, will increase with an increase of the A value, which means that the benzopyran moiety is bent more toward R. ... 

The specific structural features of SPs affect the photochromic properties of these compounds. Since photophysical and photochemical properties of organic molecules depend essentially on their structure in the excited state, we shall examine the nature of the structural changes in these molecules upon photoexcitation. The nature of such changes, in turn, depends on the type of electronic transition that converts the molecule into a photochemically active state (PCAS). The converstion of SP1-SP4 molecules to a PCAS upon UV irradiation with k > 300 nm is known to be due to electronic transitions of the n-n type in molecules without EA substituents and of the nn -jt 7t type in molecules with EA substituents in the benzopyran moiety.29 These transitions are characterized by intramolecular charge transfer (ICT), mainly from the l orbital of the oxygen atom and the 7t orbital of the C(3)=C(4) bond to the phenyl group and the EA substitutents. 

Thus, an additional benzene nucleus at the 5- and 6-positions of the benzopyran moiety and the N02 group on the added ring cause some contraction and strengthening ofthe Cspiro-Obond in SP7 compared to SP1-SP6. This fact is consistent with the decreased photochemical activity of naphthospiropyrans (NSPs). 

It was demonstrated in Section 7.2.1.3 that the efficiency of orbital hyperconjugation in the spiro center depends both on the geometric configuration of the LEPs of the heteroatoms and adjacent bonds and on the electronic properties of the heteroatoms. Since symmetrical spiropyrans contain the same heteroatoms in the spiro center, efficiency of n-a interactions depends mainly on the electronic state of the heteroatoms as determined by the nature and positions of substituents in the benzopyran moiety. 

Variation of the structure of the heterocyclic nucleus and benzopyran moieties of the SP molecule has no substantial effect on the free energy of activation of the SP. 

The annellation of a benzene ring to the 5 and 6 positions of the benzopyran moiety in CH2, instead of the pyridine ring in CHI, does not essentially affect the structure of the naphthopyran fragment. The pyran rings in CHI and CH2 are nonplanar with folding along O- -C(2) and O- -0(3) in a similar manner as in SPs and SOs. The Cspiro-0 bond in CHI and CH2 is elongated, and the 0-CPh bond is shortened (Table 5). 

Krasieva and co-workers21 mentioned the thermochromic behavior of spiropyrans of the dithiolane series (9, 10). These data confirm that the annellation of the benzopyran moiety favors the thermochromic properties of this class of compounds. 

Further, we cyclized the methyl group on the nitrogen with the CH2 of the ethoxy linker to form a hve- or six-membered ring (Scheme 19.4) to obtain compounds that showed activity superior to that of their parent molecules. The synthesis of these molecules is outlined in Scheme 19.5. The activity of these compounds to reduce blood glucose and triglyceride in db/db mice is shown in Table 19.2. It is observed that the cyclic linker moiety improved the antidiabetic activity of the compounds compared to the N— Me ethoxy linker. The unsaturated analogs showed better activity than that of their saturated counterparts. Benzyl-protected compounds have been found to be better than free OH compounds, despite losing antioxidant activity. Further, the benzopyran moiety in these molecules were shrunk to dihydrobenzofuran and benzofuran derivatives, which showed modest antidiabetic activities. 

Flavan-3-ols, flavan-4-ols, and flavan-3,4-diols are different classes of flavonoid compounds comprising a C15 (C6-C3-C6) general structure of a benzopyran moiety (A and C rings) that presents an aromatic ring (B ring) linked to carbon C-2 of... 

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