Synthesis and reactions of new chiral linear dipeptide candidates using nalidixic acid as starting material

Article abstract of DOI:10.5560/ZNB.2014-4031

A series of dipeptide heterocyclic derivatives 4-15 were synthesized using methyl 2-{[(1-ethyl- 7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridin-3-yl)carbonyl] amino}-3-ethylbutanoate (3) as starting material. Treatment of 3 with L-phenylalanine methyl ester hydrochloride afforded the corresponding dipeptide methyl ester derivative 4, which was treated with hydrazine hydrate to afford the dipeptide acid hydrazide 5. Compound 5 was coupled with aldehyde and acetophenone derivatives to afford the corresponding Schiff bases 6a-f. The hydrazide derivative 5 was reacted with ethyl acetoacetate or acetone to give compounds 7 and 8, respectively. Reaction of 5 with carbon disulfide at different conditions afforded compounds 9 and 10, which were treated with hydrazine hydrate to give the 1-amino-2-dipeptido-1,3,4-triazole derivative 11. In addition, 5 was reacted with phenyl isothiocyanate to give the thiosemicarbazide derivative 12, which was cyclized with sodium hydroxide to the dipeptido 1-phenyl-1,3,4-triazole derivative 13. Finally, treatment of 13 with methyl iodide afforded the S-methyl derivative 14, which was reacted with hydrazine hydrate to give the hydrazine derivative 15.

Full text of DOI:10.5560/ZNB.2014-4031

Synthesis and Reactions of New Chiral Linear Dipeptide Candidates
Using Nalidixic Acid as Starting Material
Nagy M. Khalifaa,b, Ahmed M. Naglaha,c, Mohamed A. Al-Omara, and
Abd El-Galil E. Amra,d
a
Pharmaceutical Chemistry Department, Drug Exploration & Development Chair (DEDC),
College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia
Department of Therapeutical Chemistry, Pharmaceutical and Drug Industries Division,
b
National Research Center, Dokki 12622, Cairo, Egypt
Peptide Chemistry Department, National Research Center, Cairo, Dokki, Egypt
Applied Organic Chemistry Department, National Research Center, Cairo, Dokki, Egypt
c
d
Reprint requests to Prof. Dr. Abd El-Galil E. Amr. E-mail: aeamr1963@yahoo.com
Z. Naturforsch. 2014, 69b, 728 – 736 / DOI: 10.5560/ZNB.2014-4031
Received February 17, 2014
A series of dipeptide heterocyclic derivatives 4–15 were synthesized using methyl 2-{[(1-ethyl-
7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridin-3-yl)carbonyl]amino}-3-ethylbutanoate (3) as starting
material. Treatment of 3 with L-phenylalanine methyl ester hydrochloride afforded the corresponding
dipeptide methyl ester derivative 4, which was treated with hydrazine hydrate to afford the dipeptide
acid hydrazide 5. Compound 5 was coupled with aldehyde and acetophenone derivatives to afford
the corresponding Schiff bases 6a–f. The hydrazide derivative 5 was reacted with ethyl acetoacetate
or acetone to give compounds 7 and 8, respectively. Reaction of 5 with carbon disulfide at differ-
ent conditions afforded compounds 9 and 10, which were treated with hydrazine hydrate to give
the 1-amino-2-dipeptido-1,3,4-triazole derivative 11. In addition, 5 was reacted with phenyl isothio-
cyanate to give the thiosemicarbazide derivative 12, which was cyclized with sodium hydroxide to
the dipeptido 1-phenyl-1,3,4-triazole derivative 13. Finally, treatment of 13 with methyl iodide af-
forded the S-methyl derivative 14, which was reacted with hydrazine hydrate to give the hydrazine
derivative 15.
Key words: Nalidixic Acid, Amino Acids, Chiral Dipeptide Candidates
Introduction
peptide has also been reported [9]. These types of het-
erocyclic molecules have been shown to have vari-
In previous work, Koskin and Merchant re- ous important biological activities such as antimicro-
ported that certain substituted heterocyclic systems bial [10], antileukemic [11], antihelminthic, anticon-
were synthesized via α,β-diketoesters using 2,3- vulsant [12], antibacterial [13], antifungal [14], antitu-
pyrrolidinedione-α-acetic acid ethyl esters as start- bercular [15], and anticancer [16] activity. In contin-
ing materials [1, 2]. Peptides rarely function well as uation of our previous work, we reported the synthe-
drugs due to their low bioavailability and rapid degra- sis of some heterocyclic candidates from dipicolinic
dation within cells [3]. The conversion of these ac- acid with amino acids and he results of their biolog-
tive peptides into peptidomimetics has been a suc- ical activity screening [17 – 23]. Recently we also re-
cessful approach for making new biologically active ported the synthesis of some linear and macrocyclic
compounds [4]. Interestingly, some specific amino peptide candidates [24, 25] as PVC membrane [26] and
acids, exemplified by valine, leucine, isoleucine, glu- miniaturized potentiometric sensors [27]. In view of
tamine, and phenylalanine, were reported early on to these observations and as a continuation of our previ-
have anti-inflammatory properties [5 – 8]. Addition- ous work in peptide-heterocyclic chemistry, we have
ally, the specific inhibition of the inflammatory en- synthesized some new dipeptide candidates that are
zyme cyclooxygenase-2 (COX-2) by the natriuretic bonded to a nalidixic acid moiety.
© 2014 Verlag der Zeitschrift für Naturforschung, Tübingen · http://znaturforsch.com
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
729
Scheme 1. Synthetic route to compounds 2–6.
Results and Discussion
in dichloromethane afforded the corresponding dipep-
tide methyl ester derivative 4, which was treated with
methanolic hydrazine hydrate to afford the correspond-
ing dipeptide acid hydrazide 5. Compound 5 was con-
Chemistry
In the present study, we describe the synthesis densed with appropriate ketonic derivatives to afford
and characterization of chiral dipeptides containing the corresponding Schiff bases 6a–f (Scheme 1).
a nalidixic acid moiety and chiral amino acids. Syn-
Thehydrazidederivative5wasreactedwithrefluxing
thesis of the acid 3 as starting material from coupling ethyl acetoacetate or acetone to give the corresponding
of 1 (nalidixic acid) with L-isoleucine methyl ester dipeptide pyrazole and dimethyl hydrazone deriva-
gave the corresponding peptide methyl ester 2, which tives 7 and 8, respectively. Reaction of hydrazide 5
was hydrolyzed with methanolic sodium hydroxide ac- with carbon disulfide at room temperature afforded
cording to the reported procedure [24]. Treatment of the corresponding potassium salt 9, which was cy-
carboxamide acid 3 with L-phenylalanine methyl ester clized in the presence of potassium hydroxide to the
hydrochloride in the presence of ethyl chloroformate oxadiazole derivative 10. The latter compound can be
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

730
N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
Scheme 2. Synthetic route to compounds 7–11.
obtained directly from compound 5 by heating with 1-phenyl-1,3,4-triazole derivative 13. Finally, treat-
carbon disulfide. Treatment of compounds 9 and 10 ment of 13 with methyl iodide in DMF in the pres-
with hydrazine hydrate gave the corresponding 1-amino ence of anhydrous potassium carbonate afforded the
2-dipeptido-1,3,4-triazole derivative 11 (Scheme 2).
corresponding S-methyl derivative 14, which was re-
The dipeptide hydrazide derivative 5 was reacted acted with hydrazine hydrate to give the hydrazine
with phenyl isothiocyanate to give the corresponding derivative 15. Compound 15 can be obtained directly
thiosemicarbazide derivative 12, which was cyclized from compound 13 by heating with hydrazine hydrate
with sodium hydroxide to the corresponding dipeptido (Scheme 3).
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
731
Scheme 3. Synthetic route to compounds 12–15.
Experimental
Optronic, P8000 polarimeter, in a 1 dm length observation
tube, at the indicated conditions, and according to the equa-
tion: [α]TD = 100α(cl)−1, where: α = observed rotation
angle, D = sodium line (λ = 589 nm), c = concentration (g
per 100 mL), l = path length in dm, and T = experimental
temperature (◦C).
Melting points were determined in open glass capillary
tubes with an Electro Thermal Digital melting point ap-
paratus (model: IA9100) and are uncorrected. Elemental
microanalysis data for carbon, hydrogen and nitrogen (Mi-
croanalytical Unit, NRC) were found within the acceptable
limits of the calculated values. Infrared spectra (KBr) were
recorded on a Nexus 670 FTIR Nicolet, Fourier Transform
infrared spectrometer. Proton nuclear magnetic resonance
(1H NMR) spectra were run in ([D6]DMSO) on Jeol 500 MHz
Synthesis of ethyl 2-[2-(1-ethyl-7-methyl-4-oxo-1,4-dihydro-
1,8-naphthyridin-3-yl)carboxamido-3-methylpentanoyl]-
amino-3-phenylpropanoate (4)
To a cold and stirred dry dichloromethane solution (25 mL,
instruments. Mass spectra were run on a MAT Finnigan −20 ◦C) of the acid 3 (1 mmol), ethyl chloroformate (1 mmol)
SSQ 7000 spectrometer, using the electron impact technique and triethylamine (1 mmol) were successively added. 10 min
(EI). Analytical thin layer chromatography (TLC) was per- later, a cold methylene chloride solution (10 mL, −20 ◦C) of
formed on silica gel aluminum sheets, 60 F254 (E. Merck). isoleucine methyl ester (1 mmol) was added. Stirring of the
Specific optical rotations were measured with an A. Krauss, cold reaction mixture (−20 ◦C) was continued for 3 h, and at
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

732
N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
r. t. for overnight. The solution was then washed with water, oxyacetophenone or 3-acetylindole (1 mmol) in absolute
1 N hydrochloric acid, 1 N sodium bicarbonate, and finally methanol (50 mL) was refluxed for 5 h with stirring. The
with water (250 mL). The dried solution (anhydrous CaCl2) reaction mixture was allowed to stand at r. t. overnight,
was evaporated, and the obtained oily residue was solidified and volatiles evaporated under reduced pressure. The
by dry ether trituration, filtered off, dried under vacuum, and obtained residue was triturated with ether, filtered off, dried,
crystallized from methanol to afford the ester 4 in 57% yield, and crystallized from ethanol to afford the corresponding
m. p. 148 – 150 ◦C. – [α]2D5 = −102 (c = 0.5, MeOH). – IR hydrazone derivatives 6a–e.
(KBr): ν = 3375, 3219 (2NH), 1738 – 1668 (4 C=O) cm−1
.
6a: Yield 69%, m. p. 143 – 145 ◦C. – [α]D25 = −184
(c = 0.5, MeOH). – IR (KBr): ν = 3382 – 3217 (3 NH),
– 1H NMR (500 MHz, [D6]DMSO): δ = 0.95 (t, 3H, CH3),
0.98 (t, 3H, CH3), 1.09 (d, 3H, CH3), 1.40 (m, 2H, CH2),
2.35 (s, 3H, CH3), 2.61 (m, 1H, CH), 3.02 (q, 2H, CH2), 3.25
(d, 2H, CH2), 3.81 (s, 3H, OCH3), 4.56 (d, 1H, CH), 5.12
(t, 1H, CH), 6.85 – 8.11 (m, 8H, Ar-H), 8.96, 9.43 ppm (2s,
2H, 2NH, exchangeable with D2O). – 13C NMR (125 MHz,
[D6]DMSO): δ = 11.53, 13.27, 15.21, 25.01, 25.62, 36.87,
37.41, 49.46, 52.17, 54.22, 56.73, 112.65, 114.34, 119.02,
126.11, 127.86, 128.67, 137.96, 139.58, 148.87, 155.74,
159.84, 162.68, 170.98, 172.01, 178.33 ppm. – MS (EI,
70 eV): m/z (%) = 506 (22) [M]+. – C28H34N4O5 (506.59):
calcd. C 66.38, H 6.76, N 11.06; found C 66.30, H 6.70, N
11.00.
1720 – 1668 (4 C=O) cm−1
. –
1H NMR (500 MHz,
[D6]DMSO): δ = 0.98 (t, 3H, CH3), 1.05 (t, 3H, CH3), 1.12
(d, 3H, CH3), 1.37 (d, 6H, 2CH3), 1.43 (m, 2H, CH2),
2.32 (s, 3H, CH3), 2.67 (m, 1H, CH), 3.09 (q, 2H, CH2),
3.27 (d, 2H, CH2), 3.32 (m, 1H, CH), 4.55 (d, 1H, CH),
5.14 (t, 1H, CH), 6.94 – 8.12 (m, 13H, Ar-H + =CH), 8.52,
9.15, 11.87 ppm (3s 3H, 3NH, exchangeable with D2O). –
13C NMR (125 MHz, [D6]DMSO): δ = 11.31, 13.62, 14.53,
23.48, 24.89, 25.12, 36.35, 36.92, 37.81, 49.25, 54.99, 56.34,
113.04, 114.21, 118.87, 126.10, 126.37, 127.76, 128.73,
129.11, 132.01, 138.22, 139.42, 143.33, 148.90, 151.28,
155.74, 159.83, 162.84, 171.20, 173.54, 178.67 ppm. –
MS (EI, 70 eV): m/z (%) = 637 (8) [M]+. – C37H44N6O4
(636.78): calcd. C 69.79, H 6.96, N 13.20; found C 69.70, H
6.90, N 13.06.
Synthesis of [(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-
naphthyridine)-2-carboxamide]-2-[(3-methylpentanoyl)-
amino]-3-phenylpropionic acid hydrazide (5)
6b: Yield 62%, m. p. 201 – 203 ◦C. – [α]D25 = −96
A mixture of 4 (1 mmol) and hydrazine hydrate (16 mmol)
in methanol (10 mL) was refluxed for 6 h. The solvent was
evaporated under reduced pressure, the obtained residue was
triturated with ether, filtered off, dried, and crystallized from
methanol to afford acid hydrazide 5 in 54% yield, m. p.
183 – 185 ◦C. – [α]2D5 = −32 (c = 0.5, MeOH). – IR (KBr):
(c = 0.5, MeOH). – IR (KBr): ν = 3426 – 3194 (3 NH),
1727 – 1675 (4 C=O) cm−1
. –
1H NMR (500 MHz,
[D6]DMSO): δ = 0.95 (t, 3H, CH3), 1.02 (t, 3H, CH3), 1.14
(d, 3H, CH3), 1.42 (m, 2H, CH2), 2.30 (s, 3H, CH3), 2.68
(m, 1H, CH), 3.11 (q, 2H, CH2), 3.29 (d, 2H, CH2), 3.81 (s,
3H, CH3), 4.59 (d, 1H, CH), 5.10 (t, 1H, CH), 6.89 – 8.14 (m,
13H, Ar-H + =CH), 8.64, 9.32, 12.05 ppm (3s, 3H, 3NH, ex-
changeable with D2O). – 13C NMR (125 MHz, [D6]DMSO):
δ = 11.28, 13.56, 14.62, 24.90, 25.09, 36.98, 38.12, 49.15,
55.67, 56.23, 56.43, 113.64, 114.28, 115.03, 118.83, 126.18,
126.35, 127.73, 128.77, 130.26, 138.17, 139.58, 143.29,
148.80, 155.68, 159.76, 162.57, 163.14, 171.36, 176.45,
179.42 ppm. – MS (EI, 70 eV): m/z (%) = 624 (16) [M]+.
– C35H40N6O5 (624.73): calcd. C 67.29, H 6.45, N 13.45;
found C 67.22, H 6.40, N 13.40.
ν = 3413 – 3286 (3NH, NH2), 1725 – 1660 (4 C=O) cm−1
.
– 1H NMR (500 MHz, [D6]DMSO): δ = 0.95 (t, 3H, CH3),
1.02 (t, 3H, CH3), 1.10 (d, 3H, CH3), 1.42 (qm, 2H, CH2),
2.31 (s, 3H, CH3), 2.64 (m, 1H, CH), 3.12 (q, 2H, CH2),
3.21 (d, 2H, CH2), 4.29 (s, 2H, NH2, exchangeable with
D2O), 4.58 (d, 1H, CH), 5.10 (t, 1H, CH), 6.91 – 8.13 (m, 8H,
Ar-H), 8.83, 9.12, 11.56 ppm (3s, 3H, 3NH, exchangeable
with D2O). – 13C NMR (125 MHz, [D6]DMSO): δ = 11.37,
13.25, 14.74, 24.86, 25.19, 36.97, 38.01, 49.22, 53.81, 56.89,
112.47, 114.38, 118.90, 126.14, 127.85, 128.71, 138.17,
139.27, 149.01, 155.69, 159.88, 163.00, 171.24, 172.11,
179.02 ppm. – MS (EI, 70 eV): m/z (%) = 506 (12) [M]+.
– C27H34N6O4 (506.60): calcd. C 64.01, H 6.76, N 16.59;
found C 63.89, H 6.70, N 16.52.
6c: Yield 55%, m. p. 256 – 258 ◦C. – [α]D25 = −11
(c = 0.5, MeOH). – IR (KBr): ν = 3480 – 3215 (4NH),
1723 – 1668 (4 C=O) cm−1
. –
1H NMR (500 MHz,
[D6]DMSO): δ = 0.96 (t, 3H, CH3), 1.05 (t, 3H, CH3),
1.11 (d, 3H, CH3), 1.40 (m, 2H, CH2), 2.35 (s, 3H,
CH3), 2.60 (m, 1H, CH), 3.14 (q, 2H, CH2), 3.24 (d, 2H,
CH2), 4.68 (d, 1H, CH), 5.17 (t, 1H, CH), 6.94 – 8.13 (m,
14H, Ar-H + =CH), 8.70, 9.46, 11.83, 12.65 ppm (4s, 4H,
4NH, exchangeable with D2O). – 13C NMR (125 MHz,
Synthesis of [(1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-
naphthyridine)-2-carboxamide]-2-[(3-methylpentanoyl)-
amino]-3-phenylpropionic acid hydrazone derivatives 6a–e
A solution of hydrazide 5 (1 mmol) and an aro- [D6]DMSO): δ = 11.24, 13.61, 14.58, 24.67, 37.01, 38.10,
matic ketone, namely, 4-isopropylbenzaldehyde, 4- 49.12, 55.71, 56.43, 56.43, 105.23, 111.08, 113.84, 114.21,
methoxybenzaldehyde, 3-indolecarboxaldehyde, 4-meth- 118.65, 119.32, 121.04, 123.19, 126.02, 126.30, 127.79,
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
733
128.69, 131.21, 136.15, 138.20, 139.52, 143.21, 148.82, (d, 2H, CH2), 3.26 – 3.34 (m, 2H, 60-H, 6”-H), 3.45 – 3.52
155.59, 159.66, 162.58, 171.34, 175.47, 179.12 ppm. – MS (m, 3H, 50-H, 40-H, 60-OH, exchangeable with D2O), 4.15
(EI, 70 eV): m/z (%) = 633 [M]+. – C36H39N7O4 (633.74): (d, 1H, 50-OH, exchangeable with D2O), 4.38 (d, 1H, 40-
calcd. C 68.23, H 6.20, N 15.47; found C 68.15, H 6.14, N OH, exchangeable with D2O), 4.49 (m, 3H, 20-H, 30-H,
15.40.
30-OH, exchangeable with D2O), 4.65 (d, 1H, CH), 4.79
6d: Yield 69%, m. p. 218 – 220 ◦C. – [α]D25 = −39 (d, 1H, 20-OH, exchangeable with D2O), 5.10 (t, 1H, CH),
(c = 0.5, MeOH). – IR (KBr): ν = 3376 – 3210 (3 NH), 6.91 (d, 1H, 10-H), 6.95 – 8.12 (m, 9H, Ar-H + =CH), 8.72,
1721 – 1673 (4 C=O) cm−1
. –
1H NMR (500 MHz, 10.31, 11.57 ppm (3s, 3H, 3NH, exchangeable with D2O). –
[D6]DMSO): δ = 0.99 (t, 3H, CH3), 1.00 (t, 3H, CH3), 1.12 13C NMR (125 MHz, [D6]DMSO): δ = 11.24, 13.54, 14.62,
(d, 3H, CH3), 1.26 (s, 3H, CH3), 1.41 (m, 2H, CH2), 2.36 24.65, 24.91, 37.12, 38.02, 49.10, 55.68, 56.41, 61.22, 64.75,
(s, 3H, CH3), 2.63 (m, 1H, CH), 3.12 (q, 2H, CH2), 3.21 (d, 70.89, 72.16, 73.26, 113.82, 114.20, 118.61, 126.10, 127.74,
2H, CH2), 3.86 (s, 3H, CH3), 4.56 (d, 1H, CH), 5.14 (t, 1H, 128.65, 138.29, 139.58, 148.88, 154.18, 155.61, 159.70,
CH), 6.85 – 8.10 (m, 12H, Ar-H), 8.82, 9.17, 10.73 ppm (3s, 162.56, 171.36, 178.01, 179.23 ppm. – MS (EI, 70 eV):
3H, 3NH, exchangeable with D2O). – 13C NMR (125 MHz, m/z (%) = 669 (8) [M]+. – C33H44N6O9 (668.74): calcd. C
[D6]DMSO): δ = 11.34, 13.26, 14.52, 21.46, 24.71, 24.89, 59.27, H 6.63, N 12.57; found C 59.22, H 6.56, N 12.50.
36.92, 38.03, 49.21, 55.68, 55.97, 56.47, 113.63, 114.25,
Synthesis of N-(1-(1-(3-methyl-5-oxopyrazol-2-yl)-2-
phenylethylcarbamoyl)-2-methylbutyl)-1-ethyl-1,4-dihydro-
7-methyl-4-oxo-1,8-naphthyridine-3-carboxamide (7)
114.56, 118.79, 126.12, 126.38, 127.74, 128.71, 130.23,
138.15, 139.55, 148.78, 155.64, 159.62, 162.53, 163.21,
169.05, 171.29, 177.12, 179.00 ppm. – MS (EI, 70 eV): m/z
(%) = 638 (24) [M]+. – C36H42N6O5 (638.76): calcd. C
To a mixture of acid hydrazide 5 (10 mmol) and ethyl
67.69, H 6.63, N 13.16; found C 67.62, H 6.56, N 13.10.
6e: Yield 58%, m. p. 229 – 231 ◦C. – [α]D25 = −134
(c = 0.5, MeOH). – IR (KBr): ν = 3428 – 3186 (4NH),
acetoacetate (10 mmol) in ethanol (20 mL), a few drops of
piperidine were added. The reaction mixture was refluxed for
8 h, the precipitated solid was filtered off, washed with water,
dried, and recrystallized from ethanol to afford compound 7
in 51% yield; m. p. 260 – 262 ◦C. – [α]D25 = −104 (c = 0.5,
MeOH). – IR (KBr): ν = 3437, 3217 (2 NH), 1728 – 1675 (5
1719 – 1665 (4 C=O) cm−1
. –
1H NMR (500 MHz,
[D6]DMSO): δ = 0.98 (t, 3H, CH3), 1.00 (t, 3H, CH3),
1.10 (d, 3H, CH3), 1.23 (s, 3H, CH3), 1.43 (m, 2H, CH2),
2.33 (s, 3H, CH3), 2.67 (m, 1H, CH), 3.12 (q, 2H, CH2),
3.20 (d, 2H, CH2), 4.71 (d, 1H, CH), 5.15 (t, 1H, CH),
6.89 – 8.11 (m, 13H, Ar-H), 8.59, 9.25, 10.86, 12.05 ppm (4s,
4H, 4NH, exchangeable with D2O). – 13C NMR (125 MHz,
[D6]DMSO): δ = 11.20, 13.46, 14.54, 21.57, 24.65, 24.88,
36.95, 37.78, 49.15, 55.73, 56.48, 111.03, 112.64, 113.82,
114.24, 118.67, 119.20, 120.35, 122.58, 126.10, 126.36,
127.83, 128.78, 130.91, 135.65, 138.26, 139.51, 148.79,
155.61, 159.60, 162.5, 168.75, 171.32, 176.82, 179.23 ppm.
– MS (EI, 70 eV): m/z (%) = 647 (12) [M]+. – C37H41N7O4
(647.77): calcd. C 68.60, H 6.38, N 15.14; found C 68.42, H
6.32, N 15.10.
1
C=O) cm−1. – H NMR (500 MHz, [D6]DMSO): δ = 0.96
(t, 3H, CH3), 1.00 (t, 3H, CH3), 1.12 (d, 3H, CH3), 1.40 (m,
2H, CH2), 1.84 (s, 3H, CH3), 2.34 (s, 3H, CH3), 2.68 (m,
1H, CH), 3.10 (q, 2H, CH2), 3.26 (d, 2H, CH2), 4.24 (s,
2H, CH2), 4.55 (d, 1H, CH), 5.17 (t, 1H, CH), 6.93 – 8.14
(m, 8H, Ar-H), 8.76, 9.35 ppm (2s, 2H, 2NH, exchangeable
with D2O). – 13C NMR (125 MHz, [D6]DMSO): δ = 11.34,
13.22, 14.71, 24.85, 25.10, 26.40, 36.93, 37.89, 49.16,
51.73, 53.62, 56.42, 112.54, 114.35, 118.96, 126.07, 127.84,
128.78, 138.21, 139.45, 148.76, 155.72, 159.49, 159.81,
162.50, 162.89, 171.21, 176.46, 179.11 ppm. – MS (EI,
70 eV): m/z (%) = 572 (6) [M]+. – C31H36N6O5 (572.65):
calcd. C 65.02, H 6.34, N 14.68; found C 64.95, H 6.30, N
14.62.
Synthesis of (1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-
naphthyridine-2-carboxamide)-2-[(3-methyl-pentanoyl)
amino]-3-phenylpropionic acid mannosyl hydrazone (6f)
Synthesis of N-(propan-2-ylidene)-4-(1H-pyrrol-1-yl)-
hydrazide (8)
A mixture of hydrazide 5 (10 mmol) and D-mannose
(10 mmol) in ethanol (30 mL) containing a few drops of
A solution of acid hydrazide 5 (0.005 mol) in acetone
acetic acid was refluxed for 2 h. After cooling, the precipitate (70 mL) was refluxed for 3 h. The solvent was evaporated
was filtered off, washed with ethanol, dried, and crystallized under reduced pressure, and the obtained pale-yellow solid
from methanol to afford compound 6f in 71% yield, m. p. crystallized from ethanol to give compound 8 in 76% yield,
147 – 149 ◦C. – [α]D25 = −112 (c = 0.5, MeOH). – IR (KBr): m. p. 184 – 186 ◦C. – [α]2D5 = −136 (c = 0.5, MeOH). – IR
ν = 3486 – 3194 (OH, NH), 1728 – 1663 (4 C=O) cm−1. – (KBr): ν = 3476 – 3198 (3 NH), 1725 – 1660 (4 C=O) cm−1
.
1H NMR (500 MHz, [D6]DMSO): δ = 0.95 (t, 3H, CH3), – 1H NMR (500 MHz, [D6]DMSO): δ = 0.97 (t, 3H, CH3),
1.01 (t, 3H, CH3), 1.12 (d, 3H, CH3), 1.40 (m, 2H, CH2), 1.02 (t, 3H, CH3), 1.10 (d, 3H, CH3), 1.46 (m, 2H, CH2),
2.36 (s, 3H, CH3), 2.63 (m, 1H, CH), 3.09 (q, 2H, CH2), 3.19 1.96 (s, 3H, CH3), 2.01 (s, 3H, CH3), 2.37 (s, 3H, CH3), 2.71
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

734
N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
(m, 1H, CH), 3.15 (q, 2H, CH2), 3.20 (d, 2H, CH2), 4.59 (d, 13C NMR (125 MHz, [D6]DMSO): δ = 11.35, 13.22, 14.76,
1H, CH), 5.18 (t, 1H, CH), 6.93 – 8.11 (m, 8H, Ar-H), 8.64, 24.82, 25.34, 36.91, 43.27, 49.12, 53.61, 56.49, 113.02,
9.48, 10.85 ppm (3s, 3H, 3NH, exchangeable with D2O). – 114.32, 118.91, 126.04, 127.80, 128.76, 133.87, 138.25,
13C NMR (125 MHz, [D6]DMSO): δ = 11.26, 13.21, 14.78, 139.48, 148.73, 155.69, 159.52, 160.01, 162.59, 171.28,
17.38, 24.80, 24.97, 25.12, 37.05, 38.03, 49.23, 55.64, 56.45, 178.16 ppm. – MS (EI, 70 eV): m/z (%) = 548 (18) [M]+.
113.87, 114.21, 118.73, 126.10, 127.89, 128.71, 138.27, – C28H32N6O4S (548.66): calcd. C 61.30, H 5.88, N 15.32,
139.55, 148.77, 151.68, 155.83, 159.47, 162.58, 171.25, S 5.84; found C 61.23, H 5.82, N 15.27, S 5.80.
177.34, 179.20 ppm. – MS (EI, 70 eV): m/z (%) = 547 (32)
[M]+. – C30H38N6O4 (546.66): calcd. C 65.91, H 7.01, N
Synthesis of N-(1-(1-(4-amino-5-mercapto-4H-1,2,4-triazol-
15.37; found C 65.84, H 6.90, N 15.30.
2-yl)-2-phenylethylcarbamoyl)-2-methylbutyl)-1-ethyl-7-
methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxamide
(11)
Synthesis of the potassium salt of the thiosemicarbazide
derivative 9
To a cold stirred solution of acid hydrazide 5 (10 mmol)
Method A: The potassium salt 9 (10 mmol) was suspended
in absolute ethanol (100 mL) containing potassium hydrox- in 80% hydrazine hydrate (5 mL) and the reaction mixture
ide (15 mmol), carbon disulfide (15 mmol) was added gradu- refluxed for 3 h. The formed solid was filtered off, washed
ally. The reaction mixture was stirred at room temperature for with water, dried, and finally crystallized with DMF/ethanol
8 h. A yellow precipitate of the corresponding potassium salt to afford compound 11 in 65% yield.
9 separated. Then, dry ether (100 mL) was added to complete
Method B: A solution of oxadiazole 10 (10 mmol) in
the precipitation of the formed salt which was filtered off and ethanol (20 mL) and 80% hydrazine hydrate (5 mL) was
washed with dry ether (100 mL). The potassium salt was ob- refluxed for 3 h, then allowed to cool, diluted with cold
tained in quantitative yield and used in the next step without water, and acidified with HCl. The precipitated solid was
further purification. Yield: 93%; m. p. > 300 ◦C. – IR (KBr): filtered, washed with water, dried, and recrystallized with
ν = 3480 – 3167 (4 NH), 1726 – 1664 (4 C=O) cm−1. – MS ethanol/DMF to give compound 11 in 59% yield; m. p.
(EI, 70 eV): m/z (%) = 621 (5) [M]+. – C28H33KN6O4S2 187 – 189 ◦C. – [α]2D5 = +34 (c = 0.5, MeOH). – IR (KBr):
(620.83): calcd. C 54.17, H 5.36, N 13.54, S 10.33; found ν = 3478 – 3196 (2 NH, NH2), 1726 – 1663 (3 C=O) cm−1
.
C 54.10, H 5.30, N 13.50, S 10.26.
– 1H NMR (500 MHz, [D6]DMSO): δ = 0.96 (t, 3H, CH3),
0.99 (t, 3H, CH3), 1.10 (d, 3H, CH3), 1.41 (m, 2H, CH2),
2.38 (s, 3H, CH3), 2.65 (m, 1H, CH), 3.17 (q, 2H, CH2),
3.22 (d, 2H, CH2), 4.56 (d, 1H, CH), 5.15 (t, 1H, CH), 5.87
(s, 2H, NH2, exchangeable with D2O), 6.88 – 8.11 (m, 8H,
Ar-H), 8.45, 9.39 (2s, 2H, 2NH, exchangeable with D2O),
12.98 ppm (s, 1H, SH, exchangeable with D2O). – 13C NMR
(125 MHz, [D6]DMSO): δ = 11.32, 13.28, 14.70, 24.85,
25.11, 36.84, 43.15, 49.10, 53.66, 56.45, 113.23, 114.37,
118.92, 126.08, 127.84, 128.78, 138.29, 139.56, 148.67,
155.64, 159.47, 160.05, 162.61, 167.35, 171.23, 177.59 ppm.
– MS (EI, 70 eV): m/z (%) = 562 (4) [M]+. – C28H34N8O3S
(562.69): calcd. C 59.77, H 6.09, N 19.91, S, 5.70; found C
59.70, H 6.00, N 19.84, S, 5.64.
Synthesis of N-(1-(1-(5-mercapto-1,3,4-oxadiazol-2-yl)-2-
phenylethylcarbamoyl)-2-methylbutyl)-1-ethyl-1,4-dihydro-
7-methyl-4-oxo-1,8-naphthyridine-3-carboxamide (10)
Method A: Compound 5 (10 mmol) and CS2 (10 mmol)
were added to a solution of KOH (10 mmol) in a mixture of
water/ethanol (100 mL, v/v 1 : 1). The reaction mixture was
refluxed for 3 h, and then acidified with conc. HCl. The pre-
cipitate was filtered off, washed with H2O, dried, and crys-
tallized from ethanol to afford compound 10 in 78% yield.
Method B: A solution of potassium hydroxide (15 mmol)
and the potassium salt 9 (10 mmol) in absolute ethanol
(100 mL) was refluxed for 4 h, till the evolution of H2S
ceased. The reaction mixture was diluted with water and
acidified with HCl. The precipitated solid was filtered
off, washed with water, dried, and finally crystallized
with ethanol to give compound 10 in 81% yield; m. p.
Synthesis of the hydrazinecarbothiamide derivative 12
A mixture of compound 5 (0.01 mol) and phenyliso-
243 – 245 ◦C. – [α]2D5 = −122 (c = 0.5, MeOH). – IR (KBr): thiocyanate (0.01 mol) in ethanol (50 mL) was allowed to
ν = 3389, 3246 (2 NH), 1721 – 1667 (3 C=O) cm−1. – 1H reflux for 3 h. After cooling, the obtained solid was fil-
NMR (500 MHz, [D6]DMSO): δ = 0.95 (t, 3H, CH3), 1.03 tered off, washed with cold ethanol, dried, and crystal-
(t, 3H, CH3), 1.12 (d, 3H, CH3), 1.43 (m, 2H, CH2), 2.37 lized from ethanol to yield compound 12 in 87% yield;
(s, 3H, CH3), 2.71 (m, 1H, CH), 3.14 (q, 2H, CH2), 3.18 (d, m. p. 146 – 148 ◦C. – [α]D25 = +51 (c = 0.5, MeOH). – IR
2H, CH2), 4.57 (d, 1H, CH), 5.19 (t, 1H, CH), 6.87 – 8.10 (KBr): ν = 3471 – 3168 (5 NH), 1722 – 1684 (3 C=O), 1305
(m, 8H, Ar-H), 8.63, 9.16 (2s, 2H, 2NH, exchangeable with (C=S) cm−1. – 1H NMR (500 MHz, [D6]DMSO): δ = 0.98
D2O); 12.85 ppm (s, 1H, SH, exchangeable with D2O). – (t, 3H, CH3), 1.05 (t, 3H, CH3), 1.12 (d, 3H, CH3), 1.40
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
735
(m, 2H, CH2), 2.35 (s, 3H, CH3), 2.67 (m, 1H, CH), 3.10 to give compound 14 in 68% yield, m. p. 168 – 170 ◦C. –
(q, 2H, CH2), 3.24 (d, 2H, CH2), 4.561 (d, 1H, CH), 5.13 [α]2D5 = −86 (c = 0.5, MeOH). – IR (KBr): ν = 3324, 3182
(t, 1H, CH), 6.68 – 8.15 (m, 13H, Ar-H), 8.56, 9.70, 9.86, (2 NH), 1719 – 1661 (3 C=O) cm−1. – 1H NMR (500 MHz,
10.84, 12.23 ppm (5s, 5H, 5NH, exchangeable with D2O). – [D6]DMSO): δ = 0.96 (t, 3H, CH3), 1.02 (t, 3H, CH3), 1.12
13C NMR (125 MHz, [D6]DMSO): δ = 11.29, 13.25, 14.73, (d, 3H, CH3), 1.40 (m, 2H, CH2), 2.31 (s, 3H, CH3), 2.39
24.88, 25.10, 36.95, 38.12, 49.16, 55.97, 56.42, 113.21, (s, 3H, SCH3), 2.67 (m, 1H, CH), 3.11 (q, 2H, CH2), 3.24
114.35, 118.94, 124.87, 126.11, 126.49, 127.86, 128.75, (d, 2H, CH2), 4.54 (d, 1H, CH), 5.14 (t, 1H, CH), 6.68 – 8.12
129.17, 137.23, 138.27, 139.55, 148.69, 155.64, 159.45, (m, 13H, Ar-H), 8.61, 9.46 ppm (2s, 2H, 2NH, exchange-
162.68, 171.18, 171.75, 177.54, 181.24 ppm. – MS (EI, able with D2O). – 13C NMR (125 MHz, [D6]DMSO):
70 eV): m/z (%) = 642 (6) [M]+. – C34H39N7O4S (641.78): δ = 11.35, 13.24, 14.66, 15.01, 24.79, 25.11, 36.92, 40.72,
calcd. C 63.63, H 6.13, N 15.28, S 5.00; found C 63.55, H 49.15, 53.42, 56.02, 113.28, 114.30, 118.94, 126.05, 127.85,
6.06, N 15.20, S 4.92.
128.00, 128.71, 128.76, 129.32, 130.04, 138.23, 139.54,
147.67, 148.65, 155.62, 159.58 162.75, 169.18, 171.25,
178.12 ppm. – MS (EI, 70 eV): m/z (%) = 638 (22) [M]+.
– C35H39N7O3S (637.79): calcd. C 65.91, H 6.16, N 15.37,
S 5.03; found C 65.84, H 6.10, N 15.30, S 4.97.
Synthesis of N-(1-(1-(5-mercapto-4-phenyl-4H-1,2,4-
triazol-3-yl)-2-phenylethylcarbamoyl)-2-methylbutyl)-
1-ethyl-1,4-dihydro-7-methyl-4-oxo-1,8-naphthyridine-
3-carboxamide (13)
Synthesis of N-(1-(1-(5-hydrazino-4-phenyl-4H-1,2,4-
triazol-3-yl)-2-phenylethylcarbamoyl)-2-methyl-butyl)-
1-ethyl-1,4-dihydro-7-methyl-4-oxo-1,8-naphthyridine-
3-carboxamide (15)
A solution of hydrazine carbothiamide derivative 12
(0.01 mol) in sodium hydroxide (5 mL, 2 N) was refluxed
for 3 h. The resulting solution was cooled to r. t. and acidi-
fied to pH 3 – 4 with 37% hydrochloric acid. The precipitate
formed was filtered off, washed with distilled water, dried
A
mixture of 3-(5-(methylthio)-4-phenyl-4H-1,2,4-
and crystallized from methanol to furnish the title compound triazol-3-yl) 13 (3 mmol) or the 3-(5-mercapto-4-phenyl-
13 in 79% yield, m. p. 127 – 129 ◦C. – [α]D25 = −71 (c = 0.5, 4H-1,2,4-triazol-3-yl)-derivative 14 (3 mmol) and hydrazine
MeOH). – IR (KBr): ν = 3341, 3256 (2 NH), 1720 – 1672 (3 hydrate (80%, 5 mL) was refluxed for 6 h. The reaction
C=O) cm−1. – 1H NMR (500 MHz, [D6]DMSO): δ = 0.97 mixture was evaporated under reduced pressure to remove
(t, 3H, CH3), 1.00 (t, 3H, CH3), 1.09 (d, 3H, CH3), 1.44 (m, excess hydrazine hydrate and was allowed to cool. The
2H, CH2), 2.36 (s, 3H, CH3), 2.61 (m, 1H, CH), 3.16 (q, 2H, formed solid product was filtered off, washed with ethanol,
CH2), 3.25 (d, 2H, CH2), 4.59 (d, 1H, CH), 5.22 (t, 1H, CH), and recrystallized from DMF/H2O to give compound
6.73 – 8.14 (m, 13H, Ar-H), 8.98, 11.34 (2s, 2H, 2NH, ex- 15 in 57% yield; m. p. 283 – 285 ◦C. – [α]D25 = −152
changeable with D2O), 12.82 ppm (s, 1H, SH, exchangeable (c = 0.5, MeOH). – IR (KBr): ν = 3476 – 3147 (3 NH,
1
with D2O). – 13C NMR (125 MHz, [D6]DMSO): δ = 11.38, NH2), 1723 – 1663 (3 C=O) cm−1. – H NMR (500 MHz,
13.26, 14.64, 24.81, 25.01, 36.89, 37.15, 49.12, 53.41, 55.62, [D6]DMSO): δ = 0.95 (t, 3H, CH3), 1.00 (t, 3H, CH3),
113.26, 113.77, 114.35, 117.46, 118.97, 126.02, 127.80, 1.10 (d, 3H, CH3), 1.43 (m, 2H, CH2), 2.33 (s, 3H, CH3),
128.74, 129.71, 138.25, 139.58, 144.58, 148.47, 148.69, 2.63 (m, 1H, CH), 3.17 (q, 2H, CH2), 3.25 (d, 2H, CH2),
155.68, 159.44, 162.67, 169.21, 171.19, 177.51 ppm. – MS 4.57 (d, 1H, CH), 5.19 (t, 1H, CH), 5.79 (s, 2H, NH2),
(EI, 70 eV): m/z (%) = 624 (15) [M]+. – C34H37N7O3S 6.95 – 8.11 (m, 13H, Ar-H), 8.73, 9.43, 11.87 ppm (3s, 3H,
(623.77): calcd. C 65.47, H 5.98, N 15.72, S 5.14; found C 3NH, exchangeable with D2O). – 13C NMR (125 MHz,
65.40, H 5.90, N 15.65, S 5.10.
[D6]DMSO): δ = 11.31, 13.23, 14.67, 24.75, 25.09, 37.01,
41.55, 49.11, 53.49, 56.17, 113.26, 114.32, 118.92, 126.01,
127.80, 128.10, 128.65, 128.87, 129.38, 130.12, 138.28,
139.56, 147.98, 148.60, 155.61, 159.54 162.72, 169.17,
171.35, 177.73 ppm. – MS (EI, 70 eV): m/z (%) = 621 (34)
[M]+. – C34H39N9O3 (621.73): calcd. C 65.68, H 6.32, N
20.28; found C 65.60, H 6.24, N 20.20.
Synthesis of N-(1-(1-(5-(methylthio)-4-phenyl-4H-1,2,4-
triazol-3-yl)-2-phenylethylcarbamoyl)-2-methyl-butyl)-
1-ethyl-1,4-dihydro-7-methyl-4-oxo-1,8-naphthyridine-
3-carboxamide (14)
To a stirred solution of compound 13 (0.01 mol) in an-
hydrous DMF (10 mL), K2CO3 (0.01 mol) and methyl io-
dide (0.01 mol) were added. The stirring was continued at
room temperature for 16 h. The reaction mixture was poured
Acknowledgement
The authors would like to extend their sincere appreci-
into cold water (150 mL), the resulting precipitate was col- ation to the Deanship of Scientific Research at King Saud
lected by filtration and washed with small portions of water, University for the funding of this research through the Re-
methanol and ether, dried, and crystallized from DMF/H2O search Group project no. RGP-VPP-320.
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM

736
N. M. Khalifa et al. · Chiral Linear Dipeptide Candidates
[1] H. Koskin, Rev. Faculte Sci. Univ. Istanboul 1946, 11A, [14] A. Dandia, R. Singh, S. Khaturia, C. Merienne, G. Mor-
1; Chem. Abstr. 1946, 40, 5427.
[2] J. R. Merchant, R. M. Bhandarkar, J. Indian Chem. Soc.
gant, A. Loupy, Bioorg. Med. Chem. 2006, 14,
2409 – 2417.
1963, 40, 353 – 360.
[3] R. Hirschmann, A. B. Smith III, P. A. Sprengeler in
New Perspectives in Drug Design, (Eds.: P. M. Dean,
[15] M. Saleh, I. T. Makki, R. M. Abdel-Rahman, H. M.
Faidallah, K. A. Khan, J. Chem. 2013, Article ID
819462, 8 pages.
G. Jolles, C. G. Newton), Academic Press, San Diego, [16] D. Kaminskyy, D. Khyluk, O. Vasylenko, L. Zaprutko,
1995, pp. 1 – 14. R. Lesyk, Sci. Pharm. 2011, 79, 763 – 777.
[4] M. G. Bursavich, C. W. West, D. H. Rich, Org. Lett. [17] A. E. Amr, A. M. Mohamed, A. A. Ibrahim, Z. Natur-
2001, 26, 2317 – 2320. forsch. 2003, 58b, 861 – 868.
[5] B. R. Madan, N. K. Khanna, Indian J. Med. Res. 1978, [18] A. E. Amr, Z. Naturforsch. 2005, 60b, 990 – 998.
68, 708 – 713.
[19] M. H. Abou-Ghalia, A. E. Amr, M. M. Abdalah, Z.
[6] A. L. Hemlatha, P. Divya, M. Bharathi, H. A. Parshwa-
nath, Indian J. Pathol. Microbiol. 2005, 48, 245 – 247.
[7] M. D. Wheeler, K. Ikejema, N. Enomoto, R. F. Stack-
Naturforsch. 2003, 58b, 903 – 910.
[20] A. Attia, O. I. Abdel-Salam, A. E. Amr, I. Stibor,
M. Budesinsky, Egypt. J. Chem. 2000, 43, 187 – 201.
lewitz, V. Seabra, Z. Zhong, M. Yin, P. Schemmer, [21] A. E. Amr, M. H. Abo-Ghalia, M. M. Abdalah, Z.
M. L. Rose, I. Rusyn, B. Bradford, R. G. Thurman,
Naturforsch. 2006, 61b, 1335 – 1345.
Cell. Mol. Life Sci. 1999, 56, 843 – 856.
[22] A. E. Amr, M. H. Abo-Ghalia, M. M. Abdalah, Arch.
[8] D. C. Pimenta, R. L. Melo, G. Caliendo, V. Santa-
Pharm. Chem. Life Sci. 2007, 340, 304 – 309.
gada, F. Fiorino, B. Severino, G. de Nucci, L. Juliano, [23] M. I. Hegab, A. E. Amr, F. M. E. Abdel-Megeid, Z.
M. A. Juliano, Biol. Chem. 2002, 383, 853 – 857. Naturforsch. 2002, 57b, 922 – 927.
[9] A. K. Kiemer, M. D. Lehner, T. Hartung, A. M. Voll- [24] N. M. Khalifa, A. M. Naglah, M. A. Al-Omar, M. H.
mar, Endocrinology 2002, 143, 846 – 852.
[10] S. C. Jain, J. Sinha, S. Bhagat, W. Errington, C. E.
Olsen, Synth. Commun. 2003, 33, 563 – 577.
[11] M. Rajopadhye, F. D. Popp, J. Heterocycl. Chem. 1987,
24, 1637 – 1642.
Abu-Ghalia, A. E. Amr, Z. Naturforsch. 2013, 68b,
351 – 361.
[25] M. H. Abo-Ghalia, M. Abd El-Hamid, M. A. Zweil,
A. E. Amr, S. A. Moafi, Z. Naturforsch. 2012, 67b,
806 – 818.
[12] J. S. Biradar, S. Y. Manjunath, Indian J. Chem. 2004, [26] M. A. Abounassif, M. A. Al-Omar, A. E. Amr, G. A. E.
43B, 389 – 392. Mostafa, Drug Test Anal. 2011, 3, 373 – 379.
[13] V. V. Mulwad, A. Ali Mir, J. Korean Chem. Soc. 2008, [27] A. H. Kamel, F. M. Al Romian, A. E. Amr, Eur. Chem.
52, 649 – 656.
Bull. 2013, 2, 683 – 689.
Brought to you by | University of Georgia Libraries
Authenticated
Download Date | 5/30/15 12:56 AM