Buxus alkaloids. N-benzoylcycloprotobuxin C from Buxus sempervirens

Full text of DOI:10.1023/A:1024188831456

Chemistry of Natural Compounds, Vol. 39, No. 1, 2003
ALKALOIDS. N-BENZOYLCYCLOPROTOBUXIN C
Buxus
FROM
Buxus sempervirens
B. U. Khodzhaev and R. Shakirov
UDC 547.944/945
In continuation of studies of alkaloids from
cultivated near Tashkent [1, 2], we isolated by
Buxus sempervirens
extraction with CHCl from leaves and thin branches ethereal (20.15 g) and chloroformic (4.15 g) fractions ofthe totalalkaloids.
3
The ethereal fraction was dissolved in benzene and separated according to basicity by citrate—phosphate buffer at pH
8.0-2.0 (pH intervals of 0.5). Fractions of the total alkaloids with pH 8.0, 7.5, 7.0, 6.5, and 6.0 were chromatographed over an
aluminum oxide column with elution by ether:ethanol mixtures of increasing ethanol concentration of 5, 10, 15, 20, 25, and
30% to isolate cyclobuxine-D, cyclovirobuxine-D, cycloprotobuxine-A, cycloprotobuxine-D, buxamine-E, and
isodihydrocyclomicrophyllin-A, respectively [1-4]. Compounds were identified by comparison with authentic samples.
Themother liquor (6.5g) after separation ofbuxamine-E and isodihydrocyclomicrophyllin-A wastreatedwith acetone.
The fraction soluble in acetone was chromatographed over a silica gel coulmn (1:100) with elution by
CHCl3:C6H14:C2H5OH:NH4OH (5:7:3:0.5). The volume of each eluate was 10 mL. A total of 105 fractions was collected.
Combined fractions 85-105 were treated with ethanol to afford base 1, 0.34 g, mp 231-233 C (benzene), C34H52N2O.
CH
3
N
CH
3
H
H
R
N
1 - 4
H
H C
3
1: R = C H -CO; 2: R = H;
6
5
3: R = CO-CH ; 4: R = CH
3
3
The IR spectrum of 1 (KBr, ν, cm-1) contains absorption bands at 3042 and 1455 (methylenecyclopropane ring) [5],
2960-2830 (CH –, CH –), and 1642 (N-benzoyl carbonyl).
3
2
The PMR spectrum (100 MHz, CDCl , δ, ppm, J/Hz) exhibits signals at 0.81, 0.88, 0.93, and 1.02 (s, each 3H, tertiary
3
methyls), 0.78 (3H, d, J = 7.5, CH ), 2.36 [9H, s, N(CH ) , NCH ], 7.36-7.64 (5H, m, H-Ar).
3
3 2
3
+
The mass spectrum has principal peaks for ions with m/z 504 [M] , 490, 462, 446, 424, 400, 384, 344, 104, 98, 84,
72 (100%), 71, 70, 58, 57, 56, 44.
Base hydrolysis of alkaloid 1 produced a base of formula C27H48N2 (2), [M] = 400, mp 206-208°C (ethanol). The IR
spectrum of 2 lacks an absorption band at 1642 cm-1 that is characteristic of an N-benzoyl carbonyl. The signal of aromatic
+
protons also disappears in the PMR spectrum.
+
Acetylation of 2 by acetic anhydride in pyridine forms the N-acetyl derivative with mp 232-234°C (3), [M] = 442.
Methylation of 2 according to Hess produced the N,N′-dimethyl derivative with mp 209-211°C (ethanol) that was
identical with cycloprotobuxine-A (4) (IR and mass spectra and R ).
f
Benzoylation of 2 synthesized a compound that was identical with 1. Therefore, 1 is the N-benzoyl derivative of 2.
The mass spectrometric decomposition of base 2 is analogous to that of cycloprotobuxine-C [6, 7]. The base peak with
S. Yu. Yunusov Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan,
Tashkent, fax (99871) 120 64 75, e-mail: cnc@icps.org.uz. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 45-46,
January-February, 2003. Original article submitted January 27, 2003.
0009-3130/03/3901-0052$25.00 ©2003 Plenum Publishing Corporation
52

m/z 72 confirms the presence of a dimethyl group on C-20; that with m/z 44, (NH–CH ) on C-3 of the pregnane core [8, 9].
3
The fact that methylated base
cycloprotobuxine-C [10].
Thus, the data lead tothe conclusion that base 1 isolated byus is N-benzoylcycloprotobuxine-C [10], which is observed
for the first time in plants.
2 is identical with cycloprotobuxine-A [1] proves that alkaloid 2 is
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