1-Acyldeoxyvasicinone salts as effective intermediate C- and N-acylating agents for alkaloids and amino acids

Article abstract of DOI:10.1007/s10600-006-0261-9

The reaction of deoxyvasicinone with acid chlorides of aliphatic (acetylbromide) and aromatic (benzoyl-, o-, p-methoxy-, p-nitrobenzoylchlorides) acids was studied. It was shown that 1-deoxyvasicinone salts were formed at room temperature; α-aroyloxymethylidenedeoxyvasicinones, in the presence of triethylamine at 80-85°C. It was found that acid chlorides cause 1-acyldeoxyvasicinone salts to transform into α-hydroxy-or α-aroyloxyarylidenedeoxyvasicinones, which indirectly confirmed their acylating properties. It was found that 1-acyldeoxyvasicinone salts were effective acylating agents for alkaloids (cytisine, 1,2-dihydrodeoxyvasicinone) and amino acids (glycine, β-alanine, α-aminobutyric acid) and can be used to acylate primary and secondary aliphatic and heterocyclic amines.

Full text of DOI:10.1007/s10600-006-0261-9

Chemistry of Natural Compounds, Vol. 42, No. 6, 2006
1-ACYLDEOXYVASICINONE SALTS AS EFFECTIVE INTERMEDIATE
C- AND N-ACYLATING AGENTS FOR ALKALOIDS AND AMINO ACIDS
Kh. M. Shakhidoyatov, G. P. Genjemuratova, and E Oripov
UDC 547.945+547.79+547.856.1
The reaction of deoxyvasicinone with acid chlorides of aliphatic (acetylbromide) and aromatic (benzoyl-,
o p
p
-, -methoxy-, -nitrobenzoylchlorides) acids was studied. It was shown that 1-deoxyvasicinone salts were
-aroyloxymethylidenedeoxyvasicinones, inthepresence of triethylamineat80-
formedat roomtemperature;
85°C. It was found that acid chlorides cause 1-acyldeoxyvasicinone salts to transform into α-hydroxy- or
α-aroyloxyarylidenedeoxyvasicinones, which indirectly confirmed their acylating properties. It was
found that 1-acyldeoxyvasicinone salts were effective acylating agents for alkaloids (cytisine,
1,2-dihydrodeoxyvasicinone) and amino acids (glycine, β-alanine, α-aminobutyric acid) and can be used to
acylate primary and secondary aliphatic and heterocyclic amines.
Key words: deoxyvasicinone, 1-acyldeoxyvasicinone salts, 1,2-dihydrodeoxyvasicinone, cytisine, amino acids,
acylation, acetylbromide, p-nitro-, o-, p-methoxybenzoylchlorides.
We demonstrated previously that deoxyvasicinone (1) and its substituted derivatives and homologs undergo
bromination, formylation, and other reactions [1-4]. It was found that complicated molecules can form at the N atom
(bromination in glacial aceticacid, reaction with SO , etc.) [1, 3], on the aromatic ring(nitration, sulfochlorination, bromination
3
by potassium bromate in acidic medium) [2, 4], and at the α-C atom [1, 3].
Herein we report the acylation of 1 and its 1-acyl derivatives by acid chlorides of aliphatic and aromatic acids and
acylation of cytisine and amino acids (glycine, β-alanine, α-aminobutyric acid) by 1-acyldeoxyvasicinone salts.
Acylation of 1 by benzoylchloride (BC, 2a) in a 1:1 ratio at room temperature both with and without triethylamine
(TEA) gave the 1-benzoyl derivative, 1-benzoyldeoxyvasicinone (3a).
O
O
O
O
2a - e
N
N
N
N
80 - 85°C
RCOX
2a - e
+
+
+
20°C
N
N
N
N
_
C R
OH
CORX
C OCOR
R
3a - c
1
4
5
a: R = C6H5, X = Cl; b: R = n-O2NC6H4; X = Cl; c: R = CH3, X = Br; d: R = CH3, X = Cl; e: R = n-CH3OC6H4, X = Cl
The reaction of 1 with -nitrobenzoylchloride (2b) and acetylbromide (2c) proceeded analogously to form 3b and 3c.
p
A mixture of two compounds was obtained byreaction of 1 with 2a at 80-85°C and a reagent ratio 1:2a:TEA = 1:2:1.3.
These were the product from acylation of the α-C atom, α-benzoyl-1, which exists as the more stable enol form 4a, and the
product from its further benzoylation, α-benzoyloxybenzylidene-1 (5a).
The reaction of 1 with substituted ( -nitro, -, -methoxy) benzoylchlorides (2b, d, e) proceeded analogously. The
o m
p
reaction for 1:2b, d, e = 1:1 stopped with formation of salts 3b, d, e [3]. If TEA was used for 1:2b, d, e:TEA = 1:4:2, the
diacylation products 5b, d, e, respectively, were formed exclusively.
S. Yu. Yunusov Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan,
700170, Tashkent, fax (99871) 120 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 585-589, November-
December, 2006. Original article submitted October 18, 2006.
0009-3130/06/4206-0718 ©2006 Springer Science+Business Media, Inc.
718

It was assumed that a salt of type 3 was also formed initially during acylation of 1 and its six-membered homolog [3].
Therefore, it was expected that the salts would be acylated easier than deoxyvasicinone itself and its homologs. In this instance,
the acyl groups in the 1-position with a relativelylarge electronegativityshould enhance the reaction. Furthermore, use of type
3 salts as an acylating agent might allow less reactive acyl groups to be added to the α-position of 1. 1 did not react with acid
chlorides of aliphatic acids even with heating for a long time. Acylation of 1 with acetylbromide or other aliphatic acylating
agents gave starting 1, which was also isolated pure from 3a-c by the action of water.
O
O
O
N
N
TEA
RCOCl
N
+
2a - e
+
N
N
_
N
CORX
COR
1
3a - e
6
O
N
O
O
N
N
+
N
+
N
N
COR
ROC
COR
X
R
C OH
R
C OH
_
_
X
7
a
b
9
O
O
N
N
H O
2
+
N
N
ROC
R
C OCOR
R C OCOR
_
X
10
8
The initially formed salts 3a-e lost a molecule of HCl by the action of TEA and formed a double bond between C
2
and Cα. This formed intermediate 1-acyldehydrodeoxyvasicinone (6). Attack of 6 by another molecule of acylating agent gave
salts of 1,α-diacyldeoxyvasicinone (7a), which exist as the enols 7b.
If an excess of acid chloride was used, 7 could be acylated to form 1-acyl-α-acyloxymethylidenedeoxyvasicinone
salts (8). The intermediates 7 and 8 transformed into the corresponding α-monoacyl- (9) or their further acylation products,
α-acyloxymethylidene-1 (10), through intermediate 8 upon work up of the reaction mixture with water.
This pathway was explained by the exclusive formation of 3a-c for 1:2a = 1:1 with or without TEA. An excess of acid
chloride was required to add an acyl group to the α-position and form intermediate 7 and to acylate its hydroxyl to give 10. The
need to use an excess of TEA was explained by the fact that it binds HCl released during the reaction from 3 to 7.
Considering that the reaction proceeded through intermediates 3a-e, we decided to use them as starting materials for
acylation. Therefore, we studied the reaction of 3a-c with benzoyl-, p-nitrobenzoyl-, and acetylchloride.
Chloride salt 3a reacted with benzoylchloride in the presence of TEA (1:1:1 ratio) to form a mixture of
α-hydroxybenzylidene-1 (4a) and α-benzoylhydroxybenzylidene-1 (5a) in a 1:10 ratio, respectively.
Chloride salt 3b reacted with BC to give exclusively the bis-product 5a. Such behavior of 3b was explained by
the apparently stronger electron-accepting effect of the p-nitrobenzoyl group, which causes the hydroxyl of intermediate 7b
(R = C H NO ) to become more acidic and undergo acylation to a greater extent. This effect was observed even more for
6
4
2-n
chloride salt 3a upon acylation by p-nitrobenzoylchloride. Thus, even for 3a:2b:TEA = 1:1:1 a mixture (1:2.2) of
α-p-nitrobenzoyl-1 (4b) and α-p-nitrobenzoyloxybenzylidene-1 (5c) was produced.
A similar effect was also observed using 3a:2b:TEA = 1:4:2, where exclusively 5b was formed.
The nature of the acylating agent played an important role in the acylation of 3a-c. Thus, chloride salt 3a did not react
with benzenesulfonylchloride. Appropriate work up of the reaction mixture afforded 1. Bromide salt 1-acetyl-1 (3c) behaved
similarlyupon reaction with acetylbromide and even with benzoylchloride. Attempts toacylate even such an effective acylating
agent as 1-p-nitrobenzoyldeoxyvasicinone (3b) with acetylbromide at 1:1 and even 1:2 ratios were unsuccessful. In all instances
1 was isolated. These facts were explained bythe relativelylow acylating abilityof the acetyl cation formed from acetylbromide
by TEA compared with the benzoyl cation and even more the p-nitrobenzoyl cation.
719

The results indicated that the acyl group in the 1-position of 3a-c was not replaced with another acyl moiety during
the acylation.
Because 3a-c were effective acylating agents, it should have been possible touse them to acylate primaryand secondary
amines, which was recently demonstrated [5, 6]. In this regard, we studied the reaction of 3 with certain natural amines and
amino acids.
Acylation of 1,2-dihydrodeoxyvasicinone (11) by 3a and -c proceeded readily and gave 1-benzoyl- and 1-acetyl-1,2-
dihydrodeoxyvasicinones (12a and -c).
O
O
N
N
3a, c
+ 1 HCl
+
N
N
H
COR
11
12a, c
a: R = C6H5; c: R = CH3
It is well known that acylation of amines usually produces anhydrides or acid chlorides [7, 8]. This method is often
used for relatively large quantities of reagents but is inconvenient when working with microscopic quantities of starting
materials.
Our research showed that using 3a-c to acylate small quantities of cytisine (13) gave high (94-95%) yields of the
corresponding N-acyl cytisine derivatives (14):
NH
N COR
+
3a - c
1 HCl
+
N
N
O
O
13
14a - c
a: R = C6H5; b: R = O2NC6H5; c: R = CH3
Acylation of glycine, β-alanine, and α-aminobutyric acid by 3a also proceeded smoothly to form the corresponding
benzoylamino acids in good yields. The reaction was carried out in absolute benzene to produce 15a-c in 77-95% yield. The
relatively low (77%) yield of α-benzoylaminobutyric acid (15b) compared with 15a and -c was apparently due to a slight steric
effect of the n-propyl radical next to the amino group.
The structures of the synthesized compounds were confirmed byspectral (IR, PMR, mass) methods and bycomparison
of their physicochemical characteristics with authentic samples.
Thus, a simple method for acylating microscopic quantities of cytisine and amino acids was developed. The method
is general in nature and can be used for N-acylation of primary and secondary aliphatic and heterocyclic amines.
EXPERIMENTAL
IR spectra were recorded on an IR-20 spectrometer; mass spectra, on a MX-1303 instrument; PMR spectra, on a JNM-
4H-100 instrument (TMS and HMDS internal standards, CF COOH, CDCl , and deuteropyridine solvents). The purity of
3
3
products was monitored on Silufol UV-254 plates. Deoxyvasicinone was prepared as before [9]. 1,2-Dihydrodeoxyvasicinone
was synthesized by the literature method [10].
Acylation of 1 by: a) Benzoylchloride (1:2a:TEA = 1:2:1.3). A solution of 1 (930 mg, 5 mmol) in absolute benzene
(5 mL) was stirred, treated first with a solution of TEA (0.9 mL, 6.4 mmol) in absolute benzene (3 mL) and then benzoylchloride
(1.2 mL, 10 mmol) in the same solvent (5 mL), boiled for 8 h, cooled, and treated with water (20 mL). The organic layer was
separated. The aqueous layer was extracted with benzene. The combined benzene solutions were washed twice with water and
dried over Na SO . Solvent was distilled. Chromatography over a column of alumina (CHCl :hexane eluent) isolated
2
4
3
α-hydroxybenzylidene-1 (4a, 50 mg), mp 155-156°C, R 0.68 (Al O , CHCl ).
f
2
3
3
720

PMR spectrum (CDCl , ppm): 3.257 (2H, t, β-CH ), 4.155 (2H, t, γ-CH ), 6.648-8.250 (aromatic protons). Mass
3
2
2
+
spectrum (m/z, %): 290 (50) [M] , 262 (26), 213 (8), 185 (59), 155 (4), 130 (8), 105 (41), 77 (100).
Elution by CHCl gave α-benzoyloxybenzylidene-1 (5, 560 mg), mp 181-183°C (hexane), R 0.74 (Al O , CHCl ).
IR spectrum (ν, cm ): 1588 (C=N), 1688 (C=O), 1740, 1794 (COO). PMR spectrum (Py-d , ppm): 2.915 (2H, t,
β-CH ), 3.935 (2H, t, γ-CH ), 6.75-8.10 (aromatic protons). Mass spectrum: 394 (100) [M] , 290 (5), 262 (5), 223 (3),
f
3
2
3
3
-1
5
+
2
2
185 (6). 1:2a:TEA = 1:1:1.
Analogously, boiling 1 (653 mg, 2 mmol), benzoylchloride (0.3 mL, 2 mmol), and TEA (0.25 mL, 2 mmol) in absolute
benzene (18 mL) for 8 h produced 4a (30 mg, mp 155-156°C) and 5a (400 mg, mp 181-183°C) (from hexane).
1:2a:TEA = 1:4:2.
Analogously, 1 (930 mg, 5 mmol), benzoylchloride (2.3 mL, 20 mmol), and TEA (1.4 mL, 10 mmol) produced 5a
(420 mg, mp 182-183°C from acetic anhydride);
b) o-Methoxybenzoylchloride. 1 (930 mg, 5 mmol), o-methoxybenzoylchloride (340 mg, 20 mmol), and TEA
(1.4 mL, 10 mmol) produced α-(o-methoxybenzoyl-o-methoxybenzylidene)-1 (5d, 1.24 g, 55%), mp 246-248°C (hexane), R
f
0.36 (Al O , CHCl ).
2
3
3
-1
IR spectrum (ν, cm ): 1600 (C=N), 1670 (C=O), 1730 (COO). PMRspectrum (CF COOH, ppm): 2.70 (2H, t, β-CH ),
3
2
4.00 (2H, t, γ-CH ), 3.45, 3.53 (3H, 2s, CH , CH ), 6.4-8.1 (m, aromatic protons).
2
3
3
The aqueous solution remaining after separation of the benzene extracts was made basic with NH OH solution (25%)
4
and extracted with CHCl . The organic layer was dried over Na SO . Solvent was distilled. The solid was recrystallized from
3
2
4
cyclohexane to afford 1 (0.3 g), mp 110-111°C;
c) p-Methoxybenzoylchloride. 1 (930 mg, 5 mmol), p-methoxybenzoylchloride (340 mg, 20 mmol), and TEA
(1.4 mL, 10 mmol) afforded α-(p-methoxybenzoyloxy-p-methoxybenzylidene)-1 (5e, 640 mg, 25%), mp 205-207°C (hexane),
R 0.41 (Al O , CHCl ).
f
2
3
3
-1
IR spectrum (ν, cm ): 1610 (C=N), 1680 (C=O), 1788 (COO). PMRspectrum (CF COOH, ppm): 2.80 (2H, t, β-CH ),
3
2
4.10 (2H, t, γ-CH ), 3.45 (6H, C, OCH , OCH ), 6.5-8.2 (m, aromatic protons);
2
3
3
d) p-Nitrobenzoylchloride. 1 (930 mg, 5 mmol), p-nitrobenzoylchloride (370 mg, 20 mmol), and TEA (1.4 mL,
10 mmol) afforded α-(p-nitrobenzoyloxy-p-nitrobenzylidene)-1 (5b, 70 mg, 3%), mp 227-229°C, R 0.36 (Al O , CHCl ).
f
2
3
3
-1
IR spectrum (ν, cm ): 1608 (C=N), 1700 (C=O), 1798 (COO). Mass spectrum: 422 (3), 412 (4), 379 (20), 363 (5),
352 (17), 344 (56), 335 (100), 320 (7), 314 (9), 307 (24), 298 (16), 185 (32).
Benzoylation of α-(Hydroxybenzylidene)-1 (4a). Synthesis of 5a. A mixture of 4a (30 mg, 0.16 mmol) and benzoic
anhydride (50 mg, 0.22 mmol) was heated at 95-98°C for 10 min. The temperature was increased to 110-115°C. The reaction
mixture was held at this temperature for 1 h. The solidified mass was dissolved in a small amount of ether and treated with
hexane until cloudy. The mixture was held at 0°C for 18-24 h. The resulting precipitate was filtered off, washed with hexane,
and dried. Yield of 5a, 30 mg (75%), mp 181-182°C.
Hydrolysis of 5a. Preparation of 4a. A mixture of 5a (120 mg, 0.3 mmol) and dilute HCl (1:1, 4 mL) was boiled
for 30 min, cooled, and filtered. The filtrate was diluted with water. The crystals that formed on standing were filtered off,
thoroughly washed with water, and dried to afford 4a, 70 mg (79%), mp 155-156°C.
Synthesis of 3a-c. 1-Benzoyldeoxyvasicinone chloride (3a) was prepared by a modified method [6]:
a) A mixture of 1 (1.86 g, 10 mmol) and benzoylchloride (1.2 mL) in absolute benzene (10 mL) was stirred at 0-5°C
for 3 h. The resulting precipitate was filtered off, washed with cold benzene, and dried in a vacuum desiccator to afford 3a
-1
(2.8 g, 86%), mp 278-280°C (acetone). IR spectrum (ν, cm ): 1670 (C=N), 1710 (C=O), 1850 (N–C=O);
b) reaction of 1 (0.93 g, 5 mmol), benzoylchloride (0.6 mL, 5 mmol), and TEA (0.6 mL, 6.4 mmol) at 20-23°C afforded
3a (0.58 g, 36%), mp 278-280°C.
1-p-Nitrobenzoyldeoxyvasicinone chloride (3b) was prepared by a modified method [6]: A mixture of 1 (0.93 g, 5
mmol) and p-nitrobenzoylchloride (0.95 g, 5 mmol) in absolute benzene (10 mL) was held at 3-5°C for 30 min. The resulting
-1
crystals were filtered off, washed with cold benzene, and dried to afford 3b (1.8 g, 97%), mp 209-210°C. IR spectrum (ν, cm ):
1614 (C=N), 1700 (C=O), 1847 (N–C=O).
Performing the reaction at room temperature analogously as above produced 3b (1.2 g, 65%), mp 209-210°C.
1-Acetyldeoxyvasicinone Bromide (3c). 1 (0.37 g, 20 mmol) was dissolved in absolute benzene (15 mL), treated with
acetylbromide (3 mL) in benzene (3 mL), and stirred for 1 h. The resulting precipitate was filtered off, washed with benzene,
-1
and dried to afford 3c (5.6 g, 91%), mp 269-271°C. IR spectrum (ν, cm ): 1643 (C=N), 1707 (C=O), 1846 (N–C=O).
721

Acylation of 3a-c. Acylation of 3a by Benzoylchloride. 3a (650 mg, 2 mmol) was susspended in absolute benzene
(10 mL), treated with benzoylchloride (260 mg, 2 mmol) and then TEA (0.3 mL, 2 mmol), and boiled for 3 h. Solvent was
distilled. The solid was worked up with water. The insoluble precipitate was extracted with CHCl . The organic layer was
3
washed with water and dried over Na SO . Solvent was distilled. Fractional crystallization from hexane afforded 4a (30 mg,
2
4
5.4%), mp 156-158°C, and 5a (420 mg, 54%), mp 181-183°C.
Acylation of 3b by Benzoylchloride. 3b (370 mg, 1 mmol), benzoylchloride (150 mg, 1 mmol), and TEA (100 mg,
1 mmol) afforded 5a (290 mg, 78%), mp 181-182°C.
Reaction with p-Nitrobenzoylchloride (3a:2b = 1:1). 3a (370 mg, 1 mmol), p-nitrobenzoylchloride (190 mg,
1 mmol), and TEA (100 mg) analogously to the above afforded 4b (100 mg, 3%), mp 192-195°C, and 5b (330 mg, 68%),
-1
mp 227-229°C. IR spectrum (ν, cm ): (4b) 1598 (C=N), 1652 (C=O), 3326 (OH).
p-Nitrobenzoylation of 3a. 3a (330 mg, 1 mmol) and p-nitrobenzoylchloride (750 mg, 4 mmol), and TEA (250 mg,
2 mmol) afforded 5b (290 mg, 60%), mp 226-228°C.
Reaction of 3c with Acetylbromide. 3c (130 mg, 0.5 mmol), acetylbromide (20 mg, 0.5 mmol), and TEA (0.1 mL,
0.5 mmol) under analogous conditions after the appropriate work up afforded 1 (80 mg), mp 110-111°C (hexane).
Analogous results were obtained for the reaction of 3c with benzoylchloride, 1-benzoyl-1 chloride (3a) with
benzenesulfonylchloride, and 1-p-nitrobenzoyl-1 chloride (3c) with acetylbromide for 3a-c:acid halide:TEA = 1:1:1.
Deoxyvasicinone was isolated in all instances.
Benzoylation of 11 by 3a Chloride. A solution of 11 (190 mg, 1 mmol) in absolute benzene (5 mL) was treated with
3a (330 mg). The resulting suspension was stirred at 40-50°C for 1 h and cooled to room temperature. The resulting precipitate
of 1 hydrochloride was filtered off. The benzene layer was washed three times with water and dried over Na SO . Solvent was
2
4
distilled. The solid was recrystallized from hexane to afford 12a (290 mg, 82%), R 0.55 (Silufol, CHCl :CH OH, 10:1),
f
3
3
mp 127-129°C. The melting point of a sample mixed with an authentic sample was not depressed.
1-Acetyl-1,2-dihydrodeoxyvasicinone (12b). Analogously to the above, 11 (190 mg, 1 mmol) and 3c (270 mg,
1 mmol) afforded 12b (0.21 g, 87%), mp 120-122°C (lit. [10] mp 120-122°C), R 0.30 (Silufol, CHCl :CH OH, 10:1).
f
3
3
N-Benzoylcytisine (14a). A suspension of 3a chloride (330 mg, 1 mmol) in dry acetone (3 mL) was stirred, treated
dropwise with a solution of cytisine (190 mg, 1 mmol) in acetone (3 mL), stirred for 10 min, treated with water (10 mL), and
stirred for 5-10 min. The resulting precipitate was filtered off, washed with water, and dried to afford 15a (280 mg, 95%),
mp 115-116°C (lit. [11] mp 116°C), R 0.53 (Silufol, acetone:CHCl , 1:1).
f
3
Compounds 14b, c, and 15a-c were prepared analogously.
N-p-Nitrobenzoylcytisine (14b), yield 94%, mp 206°C (acetone:hexane).
-1
IR spectrum (ν, cm ): 1652, 1634 (CO). PMR spectrum (acetone-d , ppm, J/Hz): 6.0 (1H, br.s, H-5), 6.40 (1H, dd,
6
H-3), 7.12 (2H, br.s, H-2′,6′), 7.33 (1H, dd, H-4), 8.18 (2H, d, J = 8, H-3′,5′). R 0.51 (Silufol, acetone:CHCl , 1:1).
f
3
N-Acetylcytisine (14c), yield 95%, mp 209-210°C (acetone) (lit. [11] mp 209°C), R 0.12 (Silufol, acetone:CHCl ,
f
3
1:1).
N-Benzoylglycine (15a), yield 88.5%, mp 186-187°C (water) (lit [12] mp 187°C).
N-Benzoyl-α-aminobutyric acid (16b), yield 77%, mp 145-146°C (water) (lit. [8] mp 145°C).
N-Benzoyl-β-alanine (15c), yield 88.5%, mp 118-119°C (water) (lit. [13] mp 120°C).
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