Exciton chirality method and its application to configurational and conformational studies of natural products

Harada, Nobuyuki; Nakanishi, Koji

doi:10.1021/ar50056a001

Cited by 476 publications

(268 citation statements)

References 34 publications

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“…2). The dominant negative contributions are due to the exciton chirality of the 1,2-dibenzoate [6] and the allylic benzoate [10], as shown in Fig. 2.…”

mentioning

confidence: 97%

“…1). Additionally, the orientation of the i-Pr group was established by the observed interactions between HÀC(11) and H b C (6) and H b ÀC (8), as shown in Fig. 1.…”

mentioning

confidence: 99%

“…(15) The relative configuration of 2 was determined by a NOESY experiment, which showed relevant interactions between H b ÀC(1) and H b ÀC(3), H b ÀC(6), H b ÀC (8), and H b ÀC (9), between H a ÀC(2) and Me (14), and between H a ÀC(5) and both H a À C(7) and Me (14), confirming the cis-indane fusion, as established before for 1. The absolute configuration of 2 was derived by circular dichroism (CD), with the aid of the exciton-chirality method of the corresponding 1,2-dibenzoate [6]. Thus, 2 was reacted with (E)-cinnamoyl chloride to afford the ester derivative 2a, which exhibited a negative Cotton effect in the CD spectrum.…”

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confidence: 99%

“…The associated p ! p* intramolecular charge-transfer band at 297 nm constitutes the negative contribution between the two coupled electric-dipole transition moments of the dibenzoate system of 2a, which, according to the 'dibenzoate chirality rule' [6], corresponds to the (1R,2R) absolute configuration ( Fig. 2).…”

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confidence: 99%

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Uncommon Sesquiterpenoids and New Triterpenoids fromJatropha neopauciflora (Euphorbiaceae)

García

Delgado

2006

HCA

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Dedicated to Professor Albert Eschenmoser on the occasion of his 80th birthdayEight new terpenoids (1 -8) were isolated from the bark of Jatropha neopauciflora, together with eight known compounds. The new isolates include the sesquiterpenoids (1R,2R)-diacetoxycycloax-4(15)-ene (1) (4), (1R,2R)-dihydroxyisodauc-4-en-14-ol (5) and its acetonide 6 (artifact), as well as the two triterpenoids (3b,16b)-16-hydroxylup-20(29)-en-3-yl (E)-3-(4-hydroxyphenyl)prop-2-enoate (7) and (3b,16b)-16-hydroxyolean-18-en-3-yl (E)-3-(4-hydroxyphenyl)prop-2-enoate (8). The structures of these compounds were established by extensive 1D-and 2D-NMR spectroscopic methods, and their absolute configurations were determined by circular-dichroism (CD) experiments, and by X-ray crystallographic analysis (compound 7; Fig. 3). A plausible biosynthesis of the sesquiterpenoids 1 -5 is proposed (Scheme), starting from (À)-germacrene D as the common biogenetic precursor.

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“…2). The dominant negative contributions are due to the exciton chirality of the 1,2-dibenzoate [6] and the allylic benzoate [10], as shown in Fig. 2.…”

mentioning

confidence: 97%

“…1). Additionally, the orientation of the i-Pr group was established by the observed interactions between HÀC(11) and H b C (6) and H b ÀC (8), as shown in Fig. 1.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Uncommon Sesquiterpenoids and New Triterpenoids fromJatropha neopauciflora (Euphorbiaceae)

García

Delgado

2006

HCA

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“…2. Since these Cotton effects accorded with the UV absorption of the benzoyl group, application of Nakanishi's dibenzoate rule 7) disclosed negative chirality for these benzoyl group, i.e. (4S,5R)-configuration.…”

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confidence: 99%