Steroidal saponins from the rhizomes of Polygonatum prattii

Article abstract of DOI:10.1080/10286020.2015.1070832

Seven steroidal saponins including two new furostanol glycosides were isolated from the rhizomes of Polygonatum prattii collected from Panzhihua, Sichuan province of China. The new compounds were determined as 26-O-β-d-glucopyranosyl-(25R)-3β,22-dihydroxy-furost-5-en-7-one (pratioside G) and 26-O-β-D-glucopyranosyl-(25R)-22-hydroxy-furost-5-en-3β-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-(1→2)-[β-D-xylopyranosyl-(1→3)]-β-D-glucopyranosyl-(1→4)-β-D-galactopyranoside (pratioside H), on the basis of detailed spectroscopic and chemical analysis.

Full text of DOI:10.1080/10286020.2015.1070832

Journal of Asian Natural Products Research
ISSN: 1028-6020 (Print) 1477-2213 (Online) Journal homepage: http://www.tandfonline.com/loi/ganp20
Steroidal saponins from the rhizomes of
Polygonatum prattii
Ying Zhang, Chong-Ren Yang & Ying-Jun Zhang
To cite this article: Ying Zhang, Chong-Ren Yang & Ying-Jun Zhang (2015): Steroidal saponins
from the rhizomes of Polygonatum prattii, Journal of Asian Natural Products Research, DOI:
10.1080/10286020.2015.1070832
To link to this article: http://dx.doi.org/10.1080/10286020.2015.1070832
Published online: 26 Oct 2015.
Submit your article to this journal
Article views: 18
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=ganp20
Download by: [Orta Dogu Teknik Universitesi]
Date: 04 January 2016, At: 08:41

Journal of Asian Natural Products Research, 2015
http://dx.doi.org/10.1080/10286020.2015.1070832
Steroidal saponins from the rhizomes of Polygonatum prattii
Ying Zhanga,b, Chong-Ren Yangb,c and Ying-Jun Zhangb*
aCollege of Pharmaceutical Engineering, Jilin Agricultural Science and Technology College, Jilin
132101, China; bState Key Laboratory of Phytochemistry and Plant Resources in West China,
Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, China; Weihe
c
Biotech Research and Development Center, Yuxi 653101, China
(Received 7 April 2015; final version received 6 July 2015)
Seven steroidal saponins including two new furostanol glycosides were isolated from
the rhizomes of Polygonatum prattii collected from Panzhihua, Sichuan province of
China. The new compounds were determined as 26-O-b-D-glucopyranosyl-(25R)-
3b,22j-dihydroxy-furost-5-en-7-one (pratioside G) and 26-O-b-D-glucopyranosyl-
(25R)-22j-hydroxy-furost-5-en-3b-O-b-D-glucopyranosyl-(1→2)-b-D-glucopyrano-
syl-(1→2)-[b-D-xylopyranosyl-(1→3)]-b-D-glucopyranosyl-(1→4)-b-D-galactopyra-
noside (pratioside H), on the basis of detailed spectroscopic and chemical analysis.
Keywords: Convallariaceae; Polygonatum prattii; steroidal saponins; pratioside G;
pratioside H; polymorphism
1. Introduction
secondary metabolites in the genus and the
morphological aspects were discussed.
In which, six new steroidal saponins,
pratiosides A, B, C, D1, E1, and F1, were
also identified from the rhizomes of
P. prattii collected from Yungui Plateau
(Chuxiong, Yunnan province, China) [5].
As a continuing research on molecular
diversity of steroidal glycosides and to
search for chemical support of polymorph-
ism in P. prattii, the phytochemical study
on the rhizomes of the same species
collected from dry-hot valley region
(Panzhihua, Sichuan province, China)
was conducted to obtain seven steroidal
saponins including two new furostanol
glycosides.
Polygonatum prattii Baker (Convallaria-
ceae), with a Chinese name “Kangding
Yuzhu,” is a polymorphic species mainly
distributed in the Western Sichuan and the
Northwestern Yunnan province of China
[1]. The fresh rhizomes are used as
substitutes of “Yuzhu” in Chinese Phar-
macopoeia by local people for the treat-
ment of lung disease, palpitations,
diabetes, and upset stomach [2–3].
It is well known that taxonomy of
genus Polygonatum is difficult due to the
complex features between genus caused by
the overlap in geographical distribution,
conspicuous intersectional transition of
interspecific and intraspecific morphologi-
cal characteristic, and complicated vari-
ation. However, plant secondary
metabolites showed important physiologi-
cal, ecological, and morphological signifi-
cance. In our previous work [4], the
correlations between the molecular evol-
ution of steroidal saponins as the main
2. Results and discussion
Five known compounds were obtained and
identified as funkioside B (3) [6], proto-
aspidistrin (4) [7], aspidistrin (5) [7],
dioscin (6) [8], and Tu2 [9] (Figure 1),
*Corresponding author. Email: zhangyj@mail.kib.ac.cn
q 2015 Taylor & Francis

2
Y. Zhang et al.
OH
O
HO
HO
O
OH
R2O
O
O
O
R1
R3O
R2O
R1
R1 R2 R3
R1 R2
1
O
H2
H
H
H
5
6
7
H
H
Gal(4-1)Glc[(3-1)Xyl](2-1)Glc
Glc[(2-1)Rha](4-1)Rha
2
3
4
Gal(4-1)Glc I[(3-1)Xyl](2-1)Glc II(2-1)Glc III
H
H2 CH3
OH Glc[(2-1)Rha](4-1)Rha(4-1)Rha
H2 CH3 Gal(4-1)Glc[(3-1)Xyl](2-1)Glc
Figure 1. Steroidal saponins 1–7 isolated from Polygonatum prattii.
respectively, on the basis of their physical
and spectroscopic data and by comparison
with reference values.
Table 1. 13C NMR spectroscopic data of
compounds 1–2 (in pyridine-d5)
Both new compounds 1 and 2 were
furostane steroidal saponins showing posi-
tive reaction to Ehrlich’s reagent, sup-
ported by the typical quaternary carbon
signals belonging to the characteristic
C-22 of furostanol skeleton at d 110.7
and d 110.9, respectively [10–11].
No.
1
2
No.
2
1
2
3
4
5
6
7
8
36.8
30.0
70.1
42.9
166.7 141.2
125.8 121.8
201.3 32.5
45.1
50.0
38.7
21.2
39.0
41.6
50.1
34.7
81.3
63.0
16.6
17.5
40.7
16.6
37.6
30.3
78.4
39.4
Gal-1
2
3
4
5
6
Glc I-1
2
3
4
102.9
73.3
75.0
79.9
76.3
60.8
104.7
81.4
87.0
70.9
77.9
63.1
104.9
81.5
77.7
71.9
78.7
62.6
The molecular formula of 1 was
assigned as C33H52O10 on the basis of the
13C NMR data (Table 1) and negative
mode ion HRESI-MS at m/z 607.3486
[M 2 H]2. The negative ion FABMS
showing a fragment ion peak at m/z 445
[M 2 162 2 H]2, together with only one
anomeric proton signal (d 4.81, d,
J ¼ 7.7 Hz) in the 1H NMR spectrum,
indicated the existence of one hexosyl
sugar unit in 1. Six carbon signals at d
105.0, 75.2, 78.6, 71.7, 78.5, 62.8 arising
from one glucosyl unit were observed in
the 13C NMR spectrum, and its linkage to
C-26-OH was further determined by the
correlation between the only anomeric
proton at d 4.81 with C-26 (d 75.3) in
HMBC spectrum. The 13C NMR spectral
data of 1 were very similar to those of
funkioside B [26-O-b-D-glucopyranosyl-
(25R)-3b, 22j-dihydroxy-furost-5-ene]
[6], except for the B-ring data. In the 13C
NMR spectrum of 1, one carbonyl unit at d
31.8
50.5
37.2
21.3
40.1
40.8
56.7
32.6
81.3
63.9
16.6
19.6
41.0
16.6
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
5
6
Glc II-1
2
3
4
5
6
Glc III-1 105.0
2
3
4
74.8
76.9
70.5
76.6
62.2
105.1
75.7
78.8
71.2
67.4
110.7 110.9
32.1
28.4
34.3
75.3
17.2
30.3
28.5
34.4
75.4
17.6
5
6
Xyl-1
2
3
4
5
26-Glc-1 105.0 105.0
2
3
4
5
6
75.2
78.6
71.7
78.5
62.8
75.2
78.6
71.9
78.5
63.0

Journal of Asian Natural Products Research
3
201.3 and a pair of olefinic carbon signals
at d 166.7 (C) and 125.8 (CH) were
observed. The IR spectrum also displayed
two absorption bands at 1675 and
1635 cm21 due to a, b-unsaturated ketone
[12]. Thus, one ketone at C-7 and the
double bond between C-5 and C-6 were
deduced. These were further confirmed by
the HMBC correlations of H-4 (d 2.62,
2.71) with C-5 (d 166.7), C-10 (d 38.7),
C-6 (d 125.8), and C-3 (d 70.1), the
olefinic proton at d 5.85 (s, H-6) with C-4
(d 42.9), C-10 (d 38.7), and C-8 (d 45.1),
and H-8 (d 2.46) with C-7 (d 201.3) and
C-10 (Figure 2). The 25R configuration
depended on the chemical shifts of H2-26,
and H3-27 [13]. Therefore, compound 1
was determined to be 26-O-b-D-glucopyr-
anosyl-(25R)-3b,22j-dihydroxy-furost-5-
en-7-one, and named pratioside G.
5.15 (d, J ¼ 7.4 Hz), 5.25 (d, J ¼ 7.8 Hz),
1
and 5.55 (d, J ¼ 7.2 Hz) in the H NMR
spectrum. All b-configuration of sugar
units were reflected by their J values.
Comparing 13C NMR spectral data of 2
with those of protoaspidistrin (26-O-b-D-
glucopyranosyl-(25R)-22j-hydroxy-fur-
ost-5-en-3b-
O-b-D-glucopyranosyl-
(1→2)-[b-D-xylopyranosyl-(1→3)]-b-D-
glucopyranosyl-(1→4)-b-D-galactopyra-
noside, 4) [7] revealed that 2 had one more
glucosyl unit (d 104.9, 81.5, 77.7, 71.9,
78.7, 62.6) than 4. The linkage of the
additional glucosyl unit was determined by
HMBC experiment (Figure 2), in which
correlations of the anomeric proton at d
5.14 (Glc II H-1) with the carbon at d 81.4
(Glc I C-2) and the terminal glucosyl
anomeric proton at d 5.55 (Glc III H-1)
with the additional glucosyl C-2 (d 81.5,
Glc II) were observed. Furthermore, other
HMBC correlations of Gal H-1 at d 4.87
with C-3 at d 78.4, Glc I H-1 at d 5.15 with
Gal C-4 at d 79.9, and Xyl H-1 at d 5.25
with Glc I C-3 at d 87.0 confirmed the
sugar linkages in 2. The configuration of
25R in 2 was also identified according to
reference [13]. The absolute configur-
ations of monosaccharides were deter-
mined as D-galactose, D-glucose, and D-
xylose, on the basis of acid hydrolysis and
GC analysis of the corresponding tri-
methylsilylated L-cysteine adducts [14].
Accordingly, pratioside H (2) was deduced
to be 26-O-b-D-glucopyranosyl-(25R)-
Compound 2 had a molecular formula
C62H102O33, as deduced by the HRESIMS
at m/z 1373.6257 [M 2 H]2. The FABMS
(negative ion mode) showed the molecular
ion peak at m/z 1374 [M]2 and fragment
ion peaks at m/z 1242 [M-132]2, 1212 [M-
162]-, 1080 [M-132-162]-, 1050 [M-162-
162]-, 918 [M-132-162-162]-, 755 [M-
132-162-162-162-H]2, 431 [M-132-162-
162-162-162-162-H]-, suggesting the
existence of one terminal pentosyl and
five hexosyl units. These were coincident
with the observation of six anomeric
proton signals at d 4.73 (d, J ¼ 7.7 Hz),
4.87 (d, J ¼ 7.8 Hz), 5.14 (d, J ¼ 7.6 Hz),
Glc I
HO
HO
O
HO
O
HO
O
O
O
HO
OH
O
OH
O
O
HO
HO
O
HO
HO
OH
OH
O
HO
O
HO
Glc II
HO
O
HO
HO
HO
O
HO
O
Glc III
H
C
OH
2
1
Figure 2. Important HMBC correlations of compounds 1 and 2.

4
Y. Zhang et al.
22j-hydroxy-furost-5-en-3b-O-b-D-glu-
copyranosyl-(1→2)-b-D-glucopyranosyl-
(1→2)-[b-D-xylopyranosyl-(1→3)]-b-D-
glucopyranosyl-(1→4)-b-D-galactopyra-
noside.
ment (Bruker, Rheinstetten, Germany),
with TMS as internal standard. VG
AutoSpe 3000 (VG, Manchester, UK)
and API Qstar Pulsar LC/TOF spec-
trometers (PE Biosystems, Waltham in
Massachusetts, America) were the instru-
ments for FABMS (negative ion mode)
and HRESIMS (negative ion mode),
respectively. GC analysis for the absolute
configuration of monosaccharides was run
on Agilent Technologies HP5890 gas
chromatograph (Agilent, Santa Clara,
America) with conditions as former work
[14]. Silica gel (200–300 mesh and 10–
40 mm, Qingdao Makall, China), MCI gel
CHP 20P (Mitsubishi, Japan), Sephadex
LH-20 (Pharmacia, Sweden), and reversed
phase silica gel RP-8 (40–63 mm, Merck,
Germany) were used for column chroma-
tography (CC).
As the main chemical constituents in
P. prattii, steroidal saponins displayed
significant differences in not only the
sapogenins, but also the sugar linkage and
sequence. Six saponins with only one form
of sugar chain (galactopyranosyl-(4→1)-
glucopyranosyl-(2→1)-glucopyranosyl)
attached to C-3-OH, but five types of
sapogenins including pennogenin, iso-
narthogenin, gentrogenin, isochiapagenin,
and (25R)-spirost-3b,12a,17a-triol-5-ene
were identified [5]. However, the present
study on the same species from dry-hot
valley region (Panzhihua, Sichuan pro-
vince) led to the isolation of seven
steroidal saponins involving only three
sapogenins, diosgenin, pennogenin and
(25R)-spirost-3b-ol-5-ene-7-one, while
these saponins displayed diversity of
sugar moieties. Two saponins have free
C-3-OH, but C-26-OH is glycosylated
with glucosyl units. Rhamnosyl and
xylosyl moieties existed in the molecules,
in addition to galactosyl and glucosyl unit,
while glucosyl unit also appeared at the
inner position linked to the aglycone
directly. Two samples were all collected
in October, and the results would provide
chemical evidences for evolution of the
morphologic diversity and the poly-
morphic of secondary metabolites in the
title plant from different environments.
3.2. Plant material
The fresh rhizomes were collected from
Panzhihua, Sichuan province, China, and
identified by Prof. Heng Li of Kunming
Institute of Botany (KIB), Chinese Acad-
emy of Sciences (CAS). A voucher speci-
men is deposited at the Herbarium of KIB,
CAS.
3.3. Extraction and isolation
The fresh rhizomes (30 kg) of P. prattii
were extracted with MeOH under reflux
for three times. After removal of the
solvent in vacuo, the MeOH extract was
suspended in H2O and then partitioned
with n-BuOH. The organic solution frac-
tion (160 g) was applied to a silica gel
(4 kg) column chromatography (CC), elut-
ing with CHCl3-MeOH-H2O (7:2.5:0.4),
to give five fractions (Frs. 1–5). Fr. 2
(14 g) was chromatographed over silica gel
3. Experimental
3.1. General experimental procedures
Optical rotations were measured on a
HORIBA SEPA-3000 automatic digital
polarimeter (JASCO, Tokyo, Japan). IR
spectra were conducted on a Bio-Rad FTS-
135 spectrometer (Bio-Rad, Hercules,
California, America) with KBr pellets.
NMR spectra were recorded in pyridine-d5
on Bruker AM-400 and DRX-500 instru-
(CHCl3-MeOH-H2O,
8:2:0.2)
and
reversed-phase Rp-8 (MeOH–H2O, 6:4–
1:0) columns to afford 1 (4 mg) and 3
(45 mg). Fr. 3 (9.5 g) was subjected to
silica gel CC eluting with CHCl3 –

Journal of Asian Natural Products Research
5
MeOH–H2O (7:3:0.5) to give 5 (60 mg).
Fr.4 (6 g) was applied to silica gel
(CHCl3 –MeOH–H2O, 7:3:0.5–6:4:1)
and MCI gel CHP-20P (MeOH–H2O,
1:1–1:0) CC to afford 6 (6 mg) and 7
(12 mg). Fr. 5 (69 g) was separated by
repeated CC over silica gel (CHCl3–
MeOH–H2O, 6:4:1), RP-8 (40–80%
MeOH), and Sephadex LH-20 (5–40%
MeOH) to yield 2 (22 mg) and 4 (2 g).
1.81 (br d, J ¼ 14.5 Hz, H-7a), 1.91-1.92
(m, H-25), 2.00 2 2.03 (2 H, m, H-1b,
24b), 2.05 2 2.06 (m, H-23b), 2.20 2 2.22
(m, H-20), 2.39 (br t, J ¼ 12.1 Hz, H-4a),
2.63 (br d, J ¼ 12.1 Hz, H-4b), 3.56 2 3.60
(m, H-26), 4.73 (d, J ¼ 7.7 Hz, H-26-Glc-1),
4.87 (d, J ¼ 7.8 Hz, H-Gal-1), 4.92
(q, J ¼ 7.2 Hz, H-16), 5.14 (d, J ¼ 7.6 Hz,
H-Glc II-1), 5.15 (d, J ¼ 7.4 Hz, H-Glc I-1),
5.25 (d, J ¼ 7.8 Hz, H-Xyl-1), 5.27
(br s, H-6), 5.55 (d, J ¼ 7.2 Hz, H-Glc
III-1). 13C NMR (pyridine-d5, 400MHz)
spectral data: see Table 1. FAB-MS
(negative ion mode): m/z 1374 [M]2, 1242
[M 2 132]2, 1212 [M 2 162]2, 1080
[M 2 132 2 162]2, 1050 [M 2 162 2
162]2, 918 [M 2 132 2 162 2 162]2,
755[M 2 132 2 162 2 162 2 162 2 H]2,
431 [M 2 132 2 162 2 162 2 162 2
162 2 162 2 H]2. HRESI-MS (negative
ion mode): m/z 1373.6257 [M 2 H]2
(calculated for C62H101O33, 1373.6225).
3.3.1. Pratioside G (1)
White amorphous powder, [a]D 294.9 (c
0.12, MeOH). IR ymax (KBr) 3440 (OH),
1675 and 1635 (a, b-unsaturated ketone)
cm21. 1H NMR (pyridine-d5, 500 MHz): d
0.91 (s, CH3-18), 0.96 (d, J ¼ 6.7 Hz,
CH3-27), 1.10 (s, CH3-19), 1.34 (d,
J ¼ 6.8 Hz, CH3-21), 1.47-1.49 (2 H, m,
H-9, 14), 1.91 (2 H, m, H-25, 17), 2.20-
2.23 (m, H-20), 2.46 (t, J ¼ 10.8 Hz, H-8),
2.62 (br t, J ¼ 11.0 Hz, H-4a), 2.71 (br d,
J ¼ 11.0 Hz, H-4b), 3.29-3.31 (m, H-15),
3.58-3.60 (m, H-26a), 3.82-3.84 (m, H-
Glc-5), 3.86-3.89 (m, H-3), 3.92–3.95 (m,
H-26b,), 4.00-4.03 (m, H-Glc-2), 4.19 (t,
J ¼ 8.8 Hz, H-Glc-3), 5.85 (s, H-6), 4.81
(d, J ¼ 7.7 Hz, H-Glc-1), 4.22 (H, t,
J ¼ 8.8 Hz, H-Glc-4), 4.39-4.41 (m, H-
Glc-6a), 4.55 (br d, J ¼ 8.6 Hz, H-Glc-6b).
13C NMR (pyridine-d5, 400 MHz) spectral
data: see Table 1. FAB-MS (negative ion
mode): m/z 607 [M 2 H]-, 445
[M 2 162 2 H]2. HRFAB-MS (negative
ion mode): m/z 607.3486 [M 2 H]2
(calculated for C33H51O10, 607.3482).
3.4. Acid hydrolysis of 2
Compound 2 (10 mg) dissolved in 2 M
HCl–dioxane (1:1, 4 ml) was hydrolyzed
at 958C for 6 h. After cooling to room
temperature, 2 ml H2O was added into the
reaction mixture, then extracted with
CHCl3 (6 ml £ 3). The CHCl3 phase was
identified as diosgenin by comparing with
authentic sample on TLC. The aqueous
layer was treated using the method as
described in reference [14], and the
absolute configurations of monosacchar-
ides were determined to be D-galactose,
D-glucose, and D-xylose respectively, on
the basis of GC analysis of their
derivatives.
3.3.2. Pratioside H (2)
White amorphous powder, [a]D 253.0
(c 1.09, MeOH). 1H NMR (pyridine-d5,
500 MHz): d 0.85 (s, CH3-18), 0.86 (s,
CH3-19), 0.87 2 0.89 (m, H-9), 0.96
(d, J ¼ 6.4 Hz, CH3-27), 1.01-1.03 (m,
H-14), 1.08 2 1.09 (m, H-12a), 1.32 (d,
J ¼ 6.3 Hz, CH3-21), 1.47 2 1.49 (m,H-11),
1.64 2 1.67(2 H, m, H-1a, 24a), 1.68 2 1.70
(m, H-23a), 1.71 (br d, J ¼ 7.7 Hz, H-12b),
Acknowledgments
The authors are grateful to members of the
Analytical Group in State Key Laboratory of
Phytochemistry and Plant Resources in West
China, Kunming Institute of Botany, for
measurements of all spectra. This work was
financially supported by the 973 Program of
Ministry of Science & Technology of China

Y. Zhang et al.
6
(2011CB915503) and the 12th Five Year
National Science & Technology Supporting
Program (2012BAI29B06).
Nat. Compd 30, 713 (1994). doi:10.1007/
BF00630609.
[7] Y. Hirai, T. Konishi, S. Sanada, Y. Ida,
and J. Shoji, Chem. Pharm. Bull. 30, 3476
(1982). doi:10.1248/cpb.30.3476.
Disclosure statement
[8] Q.A. Zheng, Y.J. Zhang, H.Z. Li, and
C.R. Yang, Steroids 69, 111 (2004).
doi:10.1016/j.steroids.2003.11.004.
[9] Y. Hirai, S. Sanada, Y. Ida, and J. Shoji,
Chem. Pharm. Bull. 34, 82 (1986). doi:10.
1248/cpb.34.82.
No potential conflict of interest was reported by
the authors.
References
[1] Kunming Institute of Botany, Chinese
Academy of Sciences, Flora Yunnanica
(Science Press, Beijing, 1997),
7, 732.
[10] X.C. Li, D.Z. Wang, and C.R. Yang,
Phytochemistry 29, 3893 (1990). doi:10.
1016/0031-9422(90)85354-I.
[2] D.W. Shi, Z.W. Wang, and Z.L. Li,
J. Chin. Med. Mater 7, 18 (1992).
[3] T.S. Liu, X.G. Yang, L.M. Gong,
Q.P. Pan, and Y. Guo, Cent. South
Pharm. 2, 216 (2008).
[4] C.R. Yang, Y. Zhang, D. Wang, and
Y.J. Zhang, Acta Bot. Yunnan. 5, 591
(2007).
[11] X.C. Li, C.R. Yang, M. Ichikawa, H.
Matsuura, R. Kasai, and K. Yamasaki,
Phytochemistry 31, 3559 (1992). doi:10.
1016/0031-9422(91)83040-R.
´
[12] A.G. Gonzelez, R. Freire, J.A. Salazar,
´
and E. Suarez, Phytochemistry 10, 1339
(1971).
[13] P.K. Agrawal, Magn. Reson. Chem. 42,
990 (2004). doi:10.1002/mrc.1474.
[14] Y. Zhang, H.Z. Li, Y.J. Zhang,
M.R. Jacob, S.I. Khan, X.C. Li, and
C.R. Yang, Steroids 8, 712 (2006).
[5] X.C. Li, C.R. Yang, H. Matsuura,
R. Kasai, and K. Yamasaki, Phytochem-
istry 2, 465 (1993).
[6] G.V. Khodakov, A.S. Shashkov,
P.K. Kintya, and A. Akimov, Chem.