MOLECULAR RECOGNITION OF -AMINO ACID ESTERS
1449
CH2CH(CH3)2 in glycine, -alanine, and leucine,
respectively] and the porphyrin macroring. Steric
repulsion is likely to direct the ester moiety toward
the hydroxy group, leading to a conformation fa-
vorable for hydrogen bonding. Presumably, the size
of the R substituent determines the most favorable
position of the hydroxy group in the benzene ring
(para, meta, or ortho). The larger the substituent, the
shorter the maximal distance between the NH2 and
C=O groups in amino acid, and the more favorable
for H-bonding is ortho position of the hydroxy group
and vice versa. The number of phenyl fragments
containing hydroxy groups also affects kas. Probably,
this is connected with the probability factor; i.e., the
greater the number of hydroxyphenyl groups, the
higher the probability for formation of associates like
A.
methyl-5-phenylporphyrin (I) and 2,8,12,18-tetra-
butyl-5-(2-methoxyphenyl)-3,7,13,17-tetramethyl-
porphyrin (II) were synthesized by the procedure
reported in [11]. The zinc complexes of 2,8,12,18-
tetrabutyl-5,15-bis(2-methoxyphenyl)-3,7,13,17-
tetramethylporphyrin (III), 2,8,12,18-tetrabutyl-5,15-
bis(3-methoxyphenyl)-3,7,13,17-tetramethylporphyrin
(IV), 2,8,12,18-tetrabutyl-5,15-bis(4-methoxyphenyl)-
3,7,13,17-tetramethylporphyrin (V), and 2,8,12,18-
tetrabutyl-3,7,13,17-tetramethyl-5,15-diphenylpor-
phyrin (X) were prepared as described in [12].
Glycine, L- -alanine, and L-leucine methyl esters
were obtained from the corresponding amino acids
according to [13].
[2,8,12,18-Tetrabutyl-5,15-bis(4-hydroxyphe-
nyl)-3,7,13,17-tetramethylporphyrinato]zinc (VI).
A solution of 0.15 ml of boron tribromide in 5 ml of
chloroform was added to a solution of 105 mg of
complex V in 10 ml of chloroform, and the mixture
was stirred for 1 h. Methanol, 5 ml, was then added,
and the mixture was stirred for 30 min, neutralized
with an ammonia solution, and evaporated. The
residue was subjected to chromatography on silica gel
using chloroform as eluent. Yield 98.5 mg (97%), Rf
0.76 (Silufol, ethyl acetate heptane, 3 : 1). IR spec-
The formation of amino acid porphyrin associates
1
1
was also studied by H NMR spectroscopy. In the H
NMR spectrum of porphyrin complex VI in the
presence of 5 equiv of glycine, the OH signal shifts
downfield by 1.4 ppm. A comparable shift (
=
1.0 ppm) was observed for porphyrin VIII in the
presence of leucine. In keeping with published data
[1], these findings indicate formation of strong hydro-
gen bonds between the carbonyl oxygen atom in the
amino acid and hydrogen atom of the hydroxy group
in the porphyrin. We can conclude that the recogni-
tion ability of arylporphyrin zinc complexes with
respect to amino acid esters in toluene depends on the
position of hydroxy groups in the benzene rings.
Hydroxyphenylporphyrin complexes in which the
hydroxy group is located in the 4 position recognize
glycine methyl ester best. o-Hydroxyphenyl-substi-
tuted compounds exhibit the greatest recognition
ability with respect to leucine methyl ester. -Alanine
methyl ester is approximately equally recognized by
porphyrins having o-, m-, and p-hydroxyphenyl
substituents. The recognition ability increases in going
from porphyrins containing one meso-hydroxyphenyl
group to those possessing two such groups. The
recognition ability of diphenylporphyrin complexes
toward amino acid esters is generally lower than that
of analogous dinaphthylporphyrin complexes.
1
trum (KBr), , cm : 3300 (OH), 1345 [ (OH)], 1275
(CO). Electronic spectrum, max, nm (log ): 570.7
1
(3.95), 533.1 (3.60), 403.3 (5.20). H NMR spectrum
of complex VI, , ppm: 10.01 s (2H, meso-H), 7.86 d
(4H, o-H), 7.19 d (4H, m-H), 4.94 s (1H, OH), 3.85 t
(8H, -CH2CH2CH2CH3), 2.42 s (12H, -CH3),
2.10 quint (8H, -CH2CH2CH2CH3), 1.61 sext (8H,
-CH2CH2CH2CH3), 0.99 t (12H, -CH2CH2CH2
1
CH3). H NMR spectrum of glycine methyl ester
complex VI associate, , ppm: 10.02 s (2H, meso-H),
7.89 d (4H, o-H), 7.21 d (4H, m-H), 6.34 s (1H, OH),
3.82 t (8H, -CH2CH2CH2CH3), 2.40 s (12H, -CH3),
2.13 quint (8H, -CH2CH2CH2CH3), 1.64 sext (8H,
-CH2CH2CH2CH3), 1.02 t (12H, -CH2CH2CH2
CH3). Found, %: C 71.61; H 7.10; N 6.40; Zn 7.43.
C52H62N4O4Zn. Calculated, %: C 71.64; H 7.12; N
6.43; Zn 7.46.
The zinc complexes of 2,8,12,18-tetrabutyl-5-(2-
hydroxyphenyl)-3,7,13,17-tetramethylporphyrin (VII),
2,8,12,18-tetrabutyl-5,15-bis(2-hydroxyphenyl)-3,7,
13,17-tetramethylporphyrin (VIII), and 2,8,12,18-tetra-
butyl-5,15-bis(3-hydroxyphenyl)-3,7,13,17-tetrame-
thylporphyrin (IX) were synthesized in a similar way.
EXPERIMENTAL
1
The H NMR spectra were recorded on a Bruker-
200 spectrometer operating at 200 MHz (CDCl3,
20 C). The IR spectrum was obtained in KBr on a
Specord M-80 instrument. The electronic absorption
spectra were measured on a Specord M-400 spectro-
photometer from solutions in chloroform. The zinc
complexes of 2,8,12,18-tetrabutyl-3,7,13,17-tetra-
[2,8,12,18-Tetrabutyl-5-(2-hydroxyphenyl)-3,7,
13,17-tetramethylporphyrinato]zinc (VII). Yield
92%. Electronic spectrum, max, nm (log ): 571.7
1
(3.91), 530.1 (3.56), 398.9 (5.11). H NMR spectrum,
, ppm: 10.01 s (1H, meso-H), 9.94 s (2H, meso-H),
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 74 No. 9 2004