Synthesis of 2-Mono- and 2,2-Bis[2-(1H-tetrazol-5-yl)ethyl] Derivatives of Dipterocarpol

Article abstract of DOI:10.1134/S107042801803017X

The azidation of 2,2-bis(2-cyanoethyl)-20-hydroxydammar-24-en-3-one afforded new tetrazole derivatives of natural dipterocarpol, 2-(2-cyanoethyl)-2-[2-(1H-tetrazol-5-yl)ethyl]-20-hydroxydammar-24-en- 3-ones, 2,2-bis[2-(1H-tetrazol-5-yl)ethyl]-20-hydroxydammar-24-en-3-one, and 2,2-bis[2-(1H-tetrazol-5-yl)- ethyl]-3-oxo-25,26,27-trinordammaran-(20S),24-olide. The structure of the final and intermediate products was determined by NMR spectroscopy and X-ray analysis.

Full text of DOI:10.1134/S107042801803017X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2018, Vol. 54, No. 3, pp. 485–489. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © E.I. Rodionov, A.A. Kovaleva, A.D. Zorina, G.L. Starova, R.E. Trifonov, 2018, published in Zhurnal Organicheskoi Khimii, 2018,
Vol. 54, No. 3, pp. 477–481.
Dedicated to Full Member of the Russian Academy of Sciences
I.P. Beletskaya on her jubilee
Synthesis of 2-Mono- and 2,2-Bis[2-(1H-tetrazol-5-yl)ethyl]
Derivatives of Dipterocarpol
E. I. Rodionova, A. A. Kovalevaa, A. D. Zorinab, G. L. Starovab, and R. E. Trifonovb*
a St. Petersburg State Institute of Technology, Moskovskii pr. 26, St. Petersburg, 190013 Russia
b St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia
*e-mail: rost_trifonov@mail.ru
Received November 18, 2017
Abstract—The azidation of 2,2-bis(2-cyanoethyl)-20-hydroxydammar-24-en-3-one afforded new tetrazole
derivatives of natural dipterocarpol, 2-(2-cyanoethyl)-2-[2-(1H-tetrazol-5-yl)ethyl]-20-hydroxydammar-24-en-
3-ones, 2,2-bis[2-(1H-tetrazol-5-yl)ethyl]-20-hydroxydammar-24-en-3-one, and 2,2-bis[2-(1H-tetrazol-5-yl)-
ethyl]-3-oxo-25,26,27-trinordammaran-(20S),24-olide. The structure of the final and intermediate products was
determined by NMR spectroscopy and X-ray analysis.
DOI: 10.1134/S107042801803017X
Dammarane triterpenoids, including dipterocarpol
(1) isolated from a number of tropical plants, are wide-
spread in nature, and they exhibit various pharmaco-
logical activities [1–3]. Chemical modification of com-
pounds of plant origin is a known synthetic approach
that makes it possible to obtain substances with
improved pharmacological profile and create new
medicinal agents. Introduction of nitrogen-containing
heterocycles such as azoles and azines into a triterpene
skeleton afforded a number of compounds with high
anti-inflammatory, antitumor, antiviral, and other kinds
of activity and simultaneously reduced side effects in-
trinsic to some unmodified natural triterpenoids [4–6].
Taking into account that tetrazolyl fragment is a meta-
bolically stable analog of carboxy and cis-amide
groups, which is capable of effectively participating in
various intermolecular interactions and acting as
an acid or base, the synthesis of tetrazolyl derivatives
of natural triterpenoids seems an important problem
[7, 8]. However, until now published data on the syn-
thesis and properties of such derivatives remain very
limited. We previously described the synthesis and
properties of two series of tetrazolyl derivatives of
dammarane triterpenoids, 3-[2-(1H-tetrazol-5-yl)-
ethoxy]dammaranes and 3-[2-(1H-tetrazol-5-yl)-
ethoxyimino)dammaranes, in which the tetrazolethyl
fragment is linked to the triterpene skeleton through
an oxygen atom [9, 10].
Herein we report the synthesis of 2,2-bis[2-(1H-
tetrazol-5-yl)ethyl]dipterocarpol derivative and the
corresponding lactone via 1,3-dipolar cycloaddition of
dimethylammonium azide to 2,2-bis(2-cyanoethyl)
derivatives 3 and 4 which were prepared by Michael
addition of acrylonitrile to dipterocarpol (1) and lac-
tone 2 in the presence of a quaternary ammonium base
(Pr4NOH, Scheme 1). The reaction was selective, and
both cyanoethyl groups entered the 2-position of the
dammarane skeleton. Analogous regioselectivity was
observed previously for other triterpenoids [11, 12].
The IR spectra of cyanoethyl derivatives 3 and 4
showed absorption bands at 2249 and 1690 cm–1 due to
stretching vibrations of the CN and C3=O carbonyl
1
13
groups. The H and C NMR spectra of 3 and 4 con-
tained signals from protons of the cyanoethyl substit-
uents (δ 1.6–2.3 ppm), C2″ and C2′ methylene carbon
atoms [δC 12.34, 12.54 (3), 12.33, 12.53 ppm (4)], C1′
and C1″ [δC 31.6, 37.50 (3), 31.10, 37.42 ppm (4)],
carbon atoms of the cyano groups [δC 118.6 (3, C3″),
119.5 ppm (4, C3′), and all protons and carbons of the
dammarane skeleton. The structure of 4 was also con-
firmed by X-ray analysis (Fig. 1). The X-ray diffrac-
tion data indicated nonequivalence of the cyanoethyl
485

RODIONOV et al.
486
Scheme 1.
NC3"
R
R
2"
3'
2'
1"
Me
Me
Me
Me
NC
i
1'
Me
Me
N
O
O
Me Me
Me Me
1, 2
3, 4
N
N
N
N
N
OH
NH
NH
Me
Me
R
H
Me
H
N
ii
N
+
Me
Me
Me
Me
NC
Me
N
N
Me
O
O
Me Me
Me Me
5
6, 7
OH
Me
O
1, 3, 5, 6, R =
; 2, 4, 7, R =
.
Me
Me
O
Me
Reagents and conditions. i: CH2=CHCN, Pr4N+ OH–, KOH, dioxane, 2 h; ii: Me2NH2+ N3–, DMF, 154°C, 15 h.
groups: the β-oriented cyanoethyl group is more steri-
cally accessible than the α-cyanoethyl group which
appears closer to the methyl group on C4. Therefore,
it was the β-oriented cyanoethyl group which was
expected to react with azides first.
The azidation of 3 and 4 was carried out under
different conditions. The reactions of 3 and 4 with
various ammonium azides in toluene or DMF at a tem-
perature below 140°C led to the formation of only
monotetrazolyl derivatives in low yields. We succeed-
C21
C23
N1
C22
O3
C20
C30
C24
O2
C29
C12
C11
C13
C17
C19
C28
C1
C9
C18
C8
C2
C16
C10
C5
C14
C25
C15
C3
O1
C4
C27
C26
C7
C31
C32
C33
C6
N2
Fig. 1. Structure of the molecule of 2,2-bis(2-cyanoethyl)-3-oxo-25,26,27-trinordammaran-(20S),24-olide (4) according to the X-ray
diffraction data.
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SYNTHESIS OF 2-MONO- AND 2,2-BIS[2-(1H-TETRAZOL-5-YL)ETHYL] DERIVATIVES
487
ed in obtaining acceptable yields of bis(tetrazolyl-
ethyl) derivatives 6 and 7 only by using excess azidat-
ing agent at a temperature approaching the boiling
point of DMF and prolonged reaction time (18 h). The
low rate of azidation of 3 and 4 may result from their
steric crowding. According to published data [13], this
factor significantly hinders 1,3-dipolar cycloaddition
of azides to nitriles in the synthesis of tetrazoles.
Tetrazolylethyl derivatives 5–7 were isolated from the
reaction mixtures by column chromatography.
oxidation of 1 with chromium(VI) oxide according to
the procedure described in [15].
The X-ray diffraction data for compound 4 were
collected on a Rigaku SuperNova diffractometer
(HyPix-3000 detector, 100 K). The structure was
solved by the direct method using Superflip program
[16] and was refined by the least-squares method in
anisotropic approximation for non-hydrogen atoms
using SHELXL [17] and Olex2 [18]. Single crystals of
4 were obtained by crystallization from ethyl acetate;
C33H48N2O3, M 520.73; orthorhombic crystal system,
space group P212121; unit cell parameters at 100(2) K:
a = 10.1708(2), b = 14.6410(3), c = 19.2303(4) Å; V =
2863.60(11) Å3; Z = 4; –13 ≤ h ≤ 10, –18 ≤ k ≤ 19,
–21 ≤ l ≤ 24. Total of 15888 reflection intensities were
measured, including 6545 independent reflections
(Rint = 0.0326, Rσ = 0.0471) used for all calculations.
Final divergence factors: R1 = 0.0401 [reflections with
I > 2σ(I)], wR2 = 0.0850; R1 = 0.0484, wR2 = 0.0900
(all independent reflections). Residual electron density:
ρmin/ρmax = 0.25/–0.21 ē/Å3; F = 0.1(5). CCDC entry
no. 1811742.
In the azidation of 3, we succeeded in isolating
appreciable amounts of both bis(tetrazolylethyl) and
mono(tetrazolylethyl) derivatives 6 and 5. The C2″
signal of 5 is located in a weaker field (δC 23.17 ppm)
than that of dinitrile 1, the signal of C3′ of the
2α-cyanoethyl group is observed at δC 120.5 ppm, and
the C3″ atom (tetrazole ring) resonated at δC 154 ppm.
These data suggest that the azidation of 3 initially
involves 2β-cyanoethyl group with formation of com-
pound 5 and that further azidation of the latter yields
bis(tetrazolylethyl) derivative 6. Analogous reaction
sequence could be inferred for dinitrile 4; however, we
did not isolate the corresponding monotetrazolyl deriv-
ative. The IR spectra of 6 and 7 lacked C≡N stretching
band, and no signal assignable to cyano group was
observed in their 13C NMR spectra (δC 118–119 ppm in
the spectra of 3 and 4). In going from nitriles 3 and 5
to bis-tetrazole 6, signals from methylene carbon
atoms of the ethylene linker shifted downfield
(δC 24.17 and 24.79 ppm), and signals of C5 in the
tetrazole rings appeared at δC 156.33 and 157.06 ppm.
3,3′-[(20S)-20-Hydroxy-3-oxodammar-24-ene-
2,2,-diyl]dipropanenitrile (3). A mixture of 2.3 mmol
of compound 1, 0.04 mol of acrylonitrile, 1.25 mL of
tetrapropylammonium hydroxide, and 1.5 mL of 30%
aqueous potassium hydroxide in 10 mL of dioxane was
stirred for 24 h at room temperature. The mixture was
poured into 100 mL of an ice–water mixture contain-
ing 3 mL of aqueous HCl. The precipitate was filtered
off, washed with water until neutral washings, dried in
air, and purified by silica gel column chromatography
using hexane–ethyl acetate (2:1) as eluent. Yield 1.0 g
(81%), colorless crystals, mp 230–233°C. IR spectrum,
ν, cm–1: 3528 (OH), 2249 (CN), 1688 (C3=O).
1H NMR spectrum (CDCl3), δC, ppm: 0.73 s (3H,
C30H3), 0.89 s (3H, C19H3), 0.93 s (3H, C18H3), 0.99 s
(3H, C28H3), 1.11 s (3H, C21H3), 1.17 s (3H, C28H3),
1.65 s (3H, C26H3), 1.71 s (3H, C27H3), 1.72 m (1H,
1′-H), 1.96 m (2H, 1′-H, 1″-H), 2.02–2.20 m (2H, 2H,
2″-H), 2.25–2.37 m (3H, 1″-H, 2′-H, 2″-H), 5.15 t (1H,
24-H, J = 6.7 Hz). 13C NMR spectrum (CDCl3), δC,
ppm: 12.34 (C2″), 12.54 (C2′), 14.10, 16.29, 17.70,
21.02, 22.63, 23.06, 25.72, 26.5, 30.11, 31.60 (C1′),
36.74, 37.50 (C1″), 40.15, 40.50, 42.27, 46.18, 48.23,
49.93, 50.27, 51.55, 51.85, 73.98, 75.28, 118.63 (C3″),
119.50 (C3′), 124.62 (C24), 131.69 (C25), 218.64 (C3).
Mass spectrum (ESI): m/z 571.42 [M + Na]+.
C36H56N2O2. Calculated: M 548.4341.
EXPERIMENTAL
The IR spectra were recorded in KBr on a Perkin
1
Elmer Spectrum BX spectrometer. The H and 13C
NMR spectra were recorded on a Bruker Avance III-
400 spectrometer at 400.13 and 100.61 MHz, respec-
tively; the chemical shifts were measured relative to
the residual proton and carbon signals of the deuterated
solvent. The mass spectra were obtained on a Bruker
MaXis instrument. Silufol plates were used for thin-
layer chromatography (eluent hexane–ethyl acetate,
4:1 or 2:1); spots were visualized by spraying with
a 5% solution of 4-methoxybenzaldehyde in ethanol
acidified with sulfuric acid, followed by heating at
100–120°C for 2–3 min. The melting points were
determined with a Wägetechnik Rapido PHMK micro
hot stage.
Dipterocarpol (1) was isolated from the Diptero-
carpus alatus latex [14]. Lactone 2 was synthesized by
2,2-Bis(2-cyanoethyl)-3-oxo-25,26,27-trinordam-
maran-(20S),24-olide (4) was synthesized in a similar
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RODIONOV et al.
488
way. Yield 67%, colorless crystals, mp 233–235°C. IR
C19H3), 1.04 s (3H, C18H3), 1.12 s (3H, C27H3), 1.13 s
(3H, C28H3), 1.19 s (3H, C21H3), 1.61 s (3H, C26H3),
1.67 s (3H, C27H3), 1.32–1.59 m (12H, CH, CH2),
2.02–2.18 m (2H, 1′-H, 1″-H), 2.33 m (1H, 2″-H),
2.97 m (2H, 2″-H), 5.12 t (1H, 24-H, J = 6.6 Hz).
13C NMR spectrum (CD3OD), δC, ppm: 14.07, 15.76,
17.26, 18.25, 22.49, 22.55, 24.18 (C2″), 24.79 (C2′),
27.74, 29.42, 31.15, 33.94, 36.90, 38.94, 40.31, 41.27,
42.54, 47.90, 51.52, 52.43, 74.90, 78.37, 124.87
(C24), 130.85 (C25), 156.33 (C3″), 157.06 (C3′), 219.92
(C3). Mass spectrum (ESI), m/z: 635.4757 [M + H]+,
657.4564 [M + Na]+. C36H58N8O2. Calculated:
M 634.4683.
spectrum, ν, cm–1: 2248 (CN), 1767 (C=O, lactone),
1
1687 (C3=O). H NMR spectrum (CDCl3), δ, ppm:
0.73 s (3H, C30H3), 0.95 s (3H, C19), 0.99 s (3H,
C18H3), 1.11 s (3H, C28H3), 1.17 s (3H, C29H3), 1.39 s
(3H, C21H3), 1.64 m (1H, 1′-H), 1.89–1.95 m (2H,
1′-H, 1″-H), 1.98–2.05 m (1H, 2″-H), 2.08–2.27 m
(3H, 2′-H, 2″-H), 2.27–2.72 m (2H, 1″-H, 2′-H).
13C NMR spectrum (CDCl3), δC, ppm: 12.33 (C2″),
12.53 (C2′), 14.66, 16.10, 17.01, 18.84, 19.51, 21.02,
23.05, 26.78, 29.11, 30.12, 31.10, 32.27, 33.64, 36.73,
37.42, 40.14, 43.19, 46.17, 48.22, 49.22, 49.82, 50.17,
51.50, 51.55, 65.92, 89.87 (C20), 118.63 (C3″), 119.49
(C3′), 176.63 (C24), 218.53 (C3). Mass spectrum (ESI):
m/z 543.3564 [M + Na]+. C33H48N2O3. Calculated:
M 520.7458.
3-Oxo-2,2-bis[2-(1H-tetrazol-5-yl)ethyl]-
25,26,27-trinordammaran-(20S),24-olide (7) was
synthesized as described above for compound 6; reac-
tion time 48 h. Yield 78%, colorless crystals, mp 154–
156°C. IR spectrum, ν, cm–1: 1766 (C=O, lactone),
Compounds 5 and 6. A mixture of 0.0017 mol of
dinitrile 3, 0.034 mol of dimethylamine hydrochloride,
and 0.034 mol of sodium azide in 12 mL of DMF was
heated for 18 h at 154°C. The mixture was cooled,
poured into 50 mL of an ice–water mixture, and
acidified to pH 2. The precipitate was filtered off,
washed with water, and dried, and the products were
isolated by silica gel column chromatography. Com-
pound 5 was eluted with hexane–ethyl acetate (1:1),
and compound 6, with ethyl acetate.
1
1690 (C3=O). H NMR spectrum (CDCl3), δ, ppm:
0.72 s (3H, C30H3), 0.89 s (3H, C19H3), 0.94 s (3H,
C18H3), 1.14 s (3H, C28H3), 1.16 s (3H, C29H3), 1.39 s
(3H, C21H3), 1.32–1.59 m (12H, CH, CH2), 1.80–
2.18 m (2H, 1′-H, 1″-H), 2.40 m (1H, 1″-H), 2.75 m
(2H, 2′-H), 3.05 m (2H, 2″-H). 13C NMR spectrum
(CDCl3), δC, ppm: 14.19, 14.62, 16.13, 17.01, 17.60,
18.92, 19.49, 20.05, 21.04, 23.21, 25.97, 29.12, 30.03,
31.10, 32.34, 33.70, 36.78, 37.12, 40.11, 43.34, 46.17,
48.64, 49.18, 49.71, 50.17, 51.48, 60.40, 91.18 (C20),
157.43 (C3″), 158.33 (C3′), 178.10 (C24), 220.32 (C3).
Mass spectrum (ESI): m/z 629.3924 [M + Na]+.
C33H50N8O3. Calculated: M 606.4006.
3-{(20S)-20-Hydroxy-3-oxo-2β-[2-(1H-tetrazol-5-
yl)ethyl]dammar-24-en-2α-yl}propanenitrile (5).
Yield 0.325 g (30%), colorless crystals, mp 116–
117°C. IR spectrum, ν, cm–1: 3458 (OH), 2249
1
(CN), 1690 (C3=O). H NMR spectrum (CDCl3), δ,
ppm: 0.74 s (3H, C30H3), 0.92 s (3H, C19H3), 0.99 s
(3H, C18H3), 1.12 s (3H, C28H3), 1.20 s (3H, C21H3),
1.64 s (3H, C26H3), 1.71 s (3H, C27H3), 1.25–1.57 m
(12H, CH, CH2), 1.79–2.09 m (2H, 1′-H, 1″-H), 2.27–
2.51 m (3H, 1″-H, 2′-H), 2.69 m (1H, 1″-H), 2.97 m
(1H, 2″-H), 5.14 t (1H, 24-H, J = 6.7 Hz). 13C NMR
spectrum (CDCl3), δC, ppm: 12.40 (C2′), 14.17, 14.66,
16.29, 17.72, 20.17, 22.57, 23.17 (C2″), 25.58, 25.73,
27.49, 30.02, 31.05, 32.6 (C1′), 33.68, 36.80, 39.03,
40.14, 40.23, 42.31, 46.28, 48.41, 49.73, 49.79, 50.28,
51.18, 52.33, 60.51, 75.93, 120.56 (C3′), 124.51 (C24),
131.78 (C25), 156.30 (C3″), 218.64 (C3). Mass spectrum
(ESI): m/z 614.4582 [M + Na]+. C36H57N5O2. Calculat-
ed: M 591.8792.
The spectral studies were carried out at the
Magnetic Resonance Research Center and Chemical
Analysis and Materials Research Center of the
St. Petersburg State University.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 17-04-00981-a).
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SYNTHESIS OF 2-MONO- AND 2,2-BIS[2-(1H-TETRAZOL-5-YL)ETHYL] DERIVATIVES
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