Short and efficient approach towards buxozine-C, an alkaloid from Buxus sempervirens

Article abstract of DOI:10.1002/ardp.200600063

Buxus alkaloids display a wide range of interesting pharmacological activities. Here, we present a short and efficient approach towards one of the alkaloids, buxozine-C. The first synthesis has been achieved with 91% yield starting from cyclovirobuxine-D by forming a tetrahydro-oxazine ring with formaldehyde at room temperature.

Full text of DOI:10.1002/ardp.200600063

Arch. Pharm. Chem. Life Sci. 2006, 339, 675–676
H.-F. Liu et al.
675
Short Communication
Short and Efficient Approach Towards Buxozine-C, an Alkaloid
from Buxus sempervirens
Hai-Feng Liu1, Min Ji1, and Jin Cai2
1 Institute of Pharmaceutical Engineering, Department of Chemistry and Chemical Engineering, Southeast
University, Nanjing, P.R. China
2 Center of Drug Discovery, China Pharmaceutical University, Nanjing, P.R. China
Buxus alkaloids display a wide range of interesting pharmacological activities. Here, we present
a short and efficient approach towards one of the alkaloids, buxozine-C. The first synthesis has
been achieved with 91% yield starting from cyclovirobuxine-D by forming a tetrahydro-oxazine
ring with formaldehyde at room temperature.
Keywords: Buxozine-C / Buxus alkaloids / Cyclovirobuxine D / Semisynthesis / Tetrahydro-oxazine /
Received: April 1, 2006; accepted: August 14, 2006
DOI 10.1002/ardp.200600063
Introduction
The Buxus plants are rich source of triterpenoid alkaloids.
Previous phytochemical studies on Buxus species have
resulted in the isolation of more than 200 of such com-
pounds [1]. In the indigenous system of medicine,
extracts of genus Buxus have been used for the treatment
of several disorders [2]. Various substituted dibasic alka-
loids with a cyclopropane ring in positions 9, 19 and sub-
stituents in positions 4 or 14 have been described [3].
Cyclovirobuxine-D 1, a primary alkaloid extracted from
the plant Buxus microphylla, is widely used clinically in
China for the treatment of cardiovascular and cerebro-
vascular diseases [4]. Despite cyclovirobuxine-D prospects
as a cardiovascular agent and the considerable excite-
ment surrounding its potential therapeutic value, sev-
eral problems associated with the drug hamper its wide-
spread usage. Central among them is the issue of bioavail-
ability deficiency [5]. Research on the congeners is one of
the feasible approaches to define the structure-activity
relationship for Buxus alkaloids.
Figure 1. Chemical structure of cyclovirobuxine-D and buxo-
zine-C.
Of all these congeners, buxozine-C 2 has been taken as
the most difficult during the conventional purification
process because of the scanty contents. Compound 2, the
first Buxus alkaloid possessing a tetrahydro-oxazine ring
joined to position 16a, 17b of the androstane skeleton,
was first isolated from Buxus sempervirens L. and its struc-
ture elucidation reported by Votickꢀ in 1977 [6].
Within the alkaloid components of the plant extracts,
the biological activity of buxozine-C 2 is unknown
because of resource deficiency. So, the partial synthesis
of alkaloid 2 is essential for the research on structure-
activity relationship for natural Buxus alkaloids. The
semisynthesis of compound 2 has not been recorded
before. Thus, a simple synthesis of buxozine-C 2 starting
from cyclovirobuxine-D 1 was developed.
Correspondence: Min Ji, Institute of Pharmaceutical Engineering, De-
partment of Chemistry and Chemical Engineering, Southeast University,
Nanjing 210096, P.R. China.
E-mail: jimin@seu.edu.cn
Fax: +86-25-83272078
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H.-F. Liu et al.
Arch. Pharm. Chem. Life Sci. 2006, 339, 675–676
added, and the mixture was stirred at room temperature. After
stirring for 15 min, TLC analysis indicated the absence of
unreacted compound 1 (Rf 0.53). The solvent was evaporated
under reduced pressure, and the residue was extracted with
CH2Cl2, washed with water and brine, and dried over MgSO4. The
solvent was removed and the residue was purified by recrystalli-
zation from ether to afford alkaloid 2 as white powder (376 mg,
91%), m. p. 138–1398C (ether, decomp.) (Votickꢀ et al., m.p.
1378C). Rf 0.76. IR (KBr) mmax cm–1: 3414, 2958, 2926, 2862, 2823,
2782, 2764, 1656, 1639, 1455, 1383, 1377, 1355, 1336, 1256,
1175, 1152, 1100, 1039, 1029, 1003, 987, 897, 839, 591. 1H-NMR
(CDCl3) (only diagnostic peaks listed): d (ppm) = 4.53 (1H, d, J = 9.6
Hz, H-27), 4.23 (1H, d, J = 9.6 Hz, H-27), 3.70 (1H, m, H-16), 2.80
(1H, m, H-20), 2.36 (3H, s, H-23), 2.28 (3H, s, H-24), 1.12 (3H, s, H-
22), 1.10 (3 H, s, H-18), 1.05 (3H, s, H-26), 0.96 (3H, s, H-25), 0.79
(3H, m, H-21), 0.58 (1H, d, J = 3.8 Hz, H-19), 0.28 (1H, d, J = 4.0 Hz,
H-19). 13C-NMR (CDCl3): d (ppm) = 88.5 (C-27), 83.6 (C-16), 71.8 (C-
3), 59.1 (C-20), 49.6 (C-17), 49.1 (C-14), 48.1 (C-8), 46.7 (C-24), 44.4
(C-13), 43.5 (C-4), 41.9 (C-5), 41.3 (C-10), 34.5 (C-12), 33.4 (C-15),
31.2 (C-1), 31.0 (C-19), 27.4 (C-26), 26.7 (C-23), 26.6 (C-6), 26.1 (C-7),
23.4 (C-2), 21.3 (C-9), 20.4 (C-11), 19.7 (C-22), 19.3 (C-18),17.4 (C-25),
16.0 (C-21). TOF-MS m/z: 415.3 (C27H46N2OH+).
Results and Discussion
Wood (excluding the bark) extract containing 66% cyclo-
virobuxine-D 1, 24% cyclobuxine-D, and 10% other Buxus
alkaloids, was purchased from Jiangsu Tenglong Biologi-
cal Technological Co. Ltd, China. The crude alkaloid was
then purified as described in the literature [7] followed
by recrystallization from acetone. The melting point of
compound 1 purified is 220–2218C (acetone, decomp.),
similar to that reported in the literature (Brown et al.,
221–2248C) [8].
Closure of compound 1 with an excess of formaldehyde
in the presence of ethanol as solvent at room tempera-
ture afforded alkaloid 2 in 91% yields.
In this Buxus alkaloid 2, the closure of the side chains
of cyclovirobuxine-D 1 forms a tetrahydro-oxazine ring
for the biogenetic cause. The postulated formulation of
compound 2 is in accordance with the number of acid
hydrogen found in the molecule [6]. Characteristically,
the TOF-MS displayed a peak of [M+H]+ at 415.3
(C27H46N2OH+, requires 415.36). The H-NMR showed the
1
presence of the methylene group (C-27) between two het-
ero atoms at 4.23 (d, J = 9.6 Hz) and 4.53 (d, J = 9.6 Hz),
while the 13C-NMR displayed the same group at 88.5. The
IR spectrum exhibited vibration of a C–O–C bond
(1100 cm–1) and a tert-amino group (1175 cm–1).
References
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Melting points are uncorrected. IR spectra were recorded in KBr
on Nicolet Impact 410 spectrophotometer (Nicolet, Madison, WI,
1
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300 MHz on Bruker AV-300 and at 500MHz on Bruker AV-500
NMR spectrometers (Bruker, Rheinstetten, Germany), respec-
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meter (Agilent, Palo Alto, CA, USA). Assignment of C atoms in13C-
NMR spectra was based on previous studies with Buxus alkaloids
[9, 10]. Analytical TLC was carried out on 0.25 mm silica gel plates
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To a solution of alkaloid 1 (402 mg, 1 mmol) in ethanol (5 mL),
formaldehyde (37% aqueous solution) (0.15 mL, 2 mmol) was
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