Stereochemistry of samarcandin-type sesquiterpenoid coumarins. Crystal structures of feshurin and nevskin

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242
0009-3130/15/5102-0242
©
2015 Springer Science+Business Media New York
Chemistry of Natural Compounds, Vol. 51, No. 2, March, 2015
STEREOCHEMISTRY OF SAMARCANDIN-TYPE SESQUITERPENOID
COUMARINS. CRYSTAL STRUCTURES OF FESHURIN AND NEVSKIN
B. Tashkhodzhaev,
1*
 K. K. Turgunov,
1
L. Yu. Izotova,
2
 and Kh. Sh. Kamoldinov
1
The crystal and molecular structures of the sesquiterpenoid coumarins feshurin and nevskin were determined
by x-ray crystal structure analyses. The absolute configuration of feshurin was established as (1
cR,2cR,6cS,9cR
and C10
cS); of nevskin, (1cR,2cR,6cR,C9cR and C10cS). The absolute configurations of eight diastereomers
of the samarcandin-type sesquiterpenoid coumarins were refined. Channel-type cavities (35.4% of the total
volume) along the crystallographic a axis formed as a result of intermolecular H-bonds and contained
disordered solvates in the crystal packing of nevskin
Keywords: sesquiterpenoid coumarins, samarcandin diastereomers, feshurin, nevskin, absolute configuration, XSA.
Plants of the genus Ferula L. (Apiaceae, celery) are rich in sesquiterpenoid coumarins with a bicyclofarnesyl skeleton
[1]. The bicyclic coumarins isolated from these plants contain five asymmetric centers in which chiral atoms C1
c, C2c, and C6c
can adopt R- or S-configurations whereas the other two (C9
cR and C10cS) remain unchanged. Eight diastereomers are formed
in the sesquiterpenoid coumarins if asymmetric C1
c, C2c, and C6c adopt the R- or S-configurations. The structures of the eight
possible natural diastereomers [2] were established at different times in samarcandin, feshurin, isosamarcandin, nevskin,
fepaldin, deacetylkellerin, episamarcandin, and ferucrin.
The absolute configurations of samarcandin (1) and several of its isomers were determined by circular dichroism [3].
The stereochemistry of 1 itself was established by an x-ray crystal structure analysis (XSA) [4]. The XSA of 1 allowed the
relative configurations of C2
c in diastereomers 2 and 3 to be corrected [4]. However, XSA was not used for a reliable and
independent establishment of the absolute configurations of the other samarcandin diastereomers. Therefore, the reported data
[2] contain errors in the assignments of the asymmetric centers. For example, the chemical structures of nevskin and isosamarcandin
(or another pair samarcandin and fepaldin) were indicated to be identical despite their different physicochemical constants [2].
1) S. Yu. Yunusov Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan,
100170, Tashkent, e-mail: [e-mail]; 2) A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences
of the Republic of Uzbekistan, 100125, Tashkent, Prosp. M. Ulugbeka, 83. Translated from Khimiya Prirodnykh Soedinenii,
No. 2, March–April, 2015, pp. 215–219. Original article submitted October 13, 2014.
O
O
R = 
H
HO
OH
OR
9'
6'
10'
2'
1'