Antimicrobial activities of a series of diphenyl (4-(aryldiazenyl)biphenyl- 4-ylamino)(pyridin-3-YL)methylphosphonates

Article abstract of DOI:10.1080/10426507.2012.680084

A series of diphenyl (4′-(aryldiazenyl)biphenyl-4-ylamino)(pyridin-3- yl)methyl-phosphonates 2-7 was synthesized in high yields and their antimicrobial activities were investigated. Some compounds showed high antimicrobial activities against Escherichia coli as a gram-negative bacterium, Bacillus subtilis and Staphylococcus aureus as gram-positive bacteria, and Candida albicans and Schccaromycies cerevisiae as fungi and at low concentrations (10-1000 μg/mL). Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Taylor and Francis Group, LLC.

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Antimicrobial Activities of
a Series of Diphenyl (4′-
(Aryldiazenyl)Biphenyl-4-Ylamino)
(Pyridin-3-YL)Methylphosphonates
Mohamed F. Abdel-Megeed a , Badr E. Badr b , Mohamed M. Azaam a
& Gamal A. El–Hiti a c
a Department of Chemistry, Faculty of Science, Tanta University,
Tanta, Egypt
b Department of Botany, Faculty of Science, Tanta University, Tanta,
Egypt
c School of Chemistry, Cardiff University, Cardiff, UK
Accepted author version posted online: 13 Apr 2012.Version of
record first published: 20 Jul 2012.
To cite this article: Mohamed F. Abdel-Megeed , Badr E. Badr , Mohamed M. Azaam & Gamal A.
El–Hiti (2012): Antimicrobial Activities of a Series of Diphenyl (4′-(Aryldiazenyl)Biphenyl-4-Ylamino)
(Pyridin-3-YL)Methylphosphonates, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:10,
1202-1207
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Phosphorus, Sulfur, and Silicon, 187:1202–1207, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.680084
ANTIMICROBIAL ACTIVITIES OF A SERIES OF DIPHENYL
(4ꢀ-(ARYLDIAZENYL)BIPHENYL-4-YLAMINO)(PYRIDIN-3-
YL)METHYLPHOSPHONATES
Mohamed F. Abdel-Megeed,1 Badr E. Badr,2 Mohamed M.
Azaam,1 and Gamal A. El–Hiti1,3
1Department of Chemistry, Faculty of Science, Tanta University, Tanta, Egypt
2Department of Botany, Faculty of Science, Tanta University, Tanta, Egypt
3School of Chemistry, Cardiff University, Cardiff, UK
GRAPHICAL ABSTRACT
Ar
N
H2N
N
i, NaNO2/HCl, 0°C
ii, Ar-O(NH)-H, 0°C
iii, aq. NaOH
NH
NH
O
O
P
P
OPh
OPh
PhO
PhO
N
N
1
2-7 (82-89%)
Ar in 2-7 = 4-hydroxynaphthalen-1-yl (2), 2-hydroxynaphthalen-1-yl (3),
2,4-dihydroxyphen-1-yl (4), 5-amino-2-hydroxyphen-1-yl (5),
2-amino-5-hydroxy-7-sulphonylnaphthalen-1-yl (6), 2-amino-5-methylphen-1-yl (7)
Abstract A series of diphenyl (4ꢁ-(aryldiazenyl)biphenyl-4-ylamino)(pyridin-3-yl)methyl-
phosphonates 2–7 was synthesized in high yields and their antimicrobial activities were
investigated. Some compounds showed high antimicrobial activities against Escherichia coli
as a gram-negative bacterium, Bacillus subtilis and Staphylococcus aureus as gram-positive
bacteria, and Candida albicans and Schccaromycies cerevisiae as fungi and at low
concentrations (10–1000 µg/mL). Supplemental materials are available for this article. Go to
the publisher’s online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to
view the free supplemental file.
Keywords α-Aminophosphonates; antimicrobial; gram-negative and gram-positive bacteria;
fungi; minimum inhibitory concentrations
INTRODUCTION
α-Aminophosphates constitute an important class of biologically active compounds
as they are structurally related to α-amino acids.1–3 Therefore, they continue to attract
Received 31 January 2012; accepted 23 March 2012.
Address correspondence to Gamal A El-Hiti, School of Chemistry, Cardiff University, Main Building, Park
Place, Cardiff CF10 3AT, UK. E-mail: el-hitiga@cardiff.ac.uk; gelhiti@yahoo.co.uk
1202

ANTIMICROBIAL ACTIVITIES OF α-AMINOPHOSPHONATES
1203
researchers because of their important pharmaceutical applications. For example, α-
aminophosphonates act as peptide mimics,4 enzyme inhibitors,5,6 antibiotics,7 crop pro-
tection agents,8 and catalytic antibodies.9 As a result, the synthesis of such compounds
were developed over the years. The synthetic procedures of α-aminophosphonates involve
use of Lewis acids, such as lanthanide triflates/MgSO4,10 InCl3,11 scandium (tris-dodecyl
sulfate),12 TaCl5-SiO2,13 Ln(OTf)3,14 lanthanide triflates/ionic liquids,15 and AlCl3.16
As part of our continuing interest in heterocyclic chemistry,17–31 we have reported
a simple and convenient approach for the synthesis of a series of 3-arylazo-2-thioxo-
2,3-dihydro-1H-quinazolin-4-ones as azodisperse dyes.32 The work reported in this pa-
per describes the synthesis of diphenyl (4ꢁ-(aryldiazenyl)biphenyl-4-ylamino)(pyridin-3-
yl)methylphosphonates. The synthesized compounds were evaluated for their antimicrobial
activities against gram-positive and gram-negative bacteria and fungi.
RESULTS AND DISCUSSION
Diazotization of diphenyl (4ꢁ-aminobiphenyl-4-ylamino)(pyridin-3-yl)methyl-
phosphonate (1) was performed by using a mixture of sodium nitrite and hydrochloric
acid at low temperature (0 ◦C) to produce the corresponding diazonium salt. Coupling of
diazonium salt of compound 1 with 1-naphthol, 2-naphthol, resorcinol, 2-aminophenol,
7-amino-4-hydroxynaphthalene-2-sulfonic acid, and 4-toludine, in aqueous sodium
hydroxide solution (10%), gave the corresponding azo dyes 2–7 (Scheme 1) in high yields
(82%–89%; Table 1).
Ar
N
H2N
N
i, NaNO2/HCl, 0°C
ii, Ar-O(NH)-H, 0°C
iii, aq. NaOH
NH
NH
O
O
P
P
OPh
OPh
PhO
PhO
N
N
1
2-7 (82-89%)
Ar in 2-7 = 4-hydroxynaphthalen-1-yl (2), 2-hydroxynaphthalen-1-yl (3),
2,4-dihydroxyphen-1-yl (4), 5-amino-2-hydroxyphen-1-yl (5),
2-amino-5-hydroxy-7-sulphonylnaphthalen-1-yl (6), 2-amino-5-methylphen-1-yl (7)
Scheme 1
The structures of diazo dyes 2–7 were confirmed by their elemental analyses and
1
various spectroscopic techniques including IR, H-NMR, and mass spectral data (see ex-
perimental section for details).
Antimicrobial Activities
The synthesized α-aminophosphonates 2–7 were screened for their in vitro antibac-
terial and antifungal activities against Escherichia coli NCIM 2065 as a gram-negative

1204
M. F. ABDEL-MEGEED ET AL.
Table 1 Synthesis of azo dyes 2–7 according to Scheme 1
Product
Ar
Color
Rubine
mp (◦C)
Yield (%)a
2
3
4
5
6
7
4-Hydroxynaphthalen-1-yl
2-Hydroxynaphthalen-1-yl
2,4-Dihydroxyphen-1-yl
5-Amino-2-hydroxyphen-1-yl
2-Amino-5-hydroxy-7-sulphonylnaphthalen-1-yl
2-Amino-5-methylphen-1-yl
179–181
190–193
171–173
149–152
161–163
201–203
88
84
89
84
83
82
Dark red
Red violet
Reddish burgundy
Burgundy
Buff
aYield of pure products after crystallization from ethanol.
bacterium, Bacillus subtilis PC 1219 and Staphylococcus aureus ATCC 25292 as gram-
positive bacteria, and Candida albicans and Schccaromycies cerevisiae as fungi. The inhibi-
tion zones were measured in triplicates and the results of antimicrobial testing are reported
in Table S1 (Supplemental Materials).
The results recorded in Table S1 showed that all compounds showed high antimicro-
bial activities against S. aureus and S. cerevisiae. Compounds 2–6 showed moderate to high
antimicrobial activities against E. coli. Compounds 2, 5, and 6 showed moderate to high
antimicrobial activities, while compounds 3, 4, and 7 showed no antimicrobial activities
against B. subtilis. It was found that compound 7 was the only active compound against C.
albicans. Compound 7 contains an NH2 group but does not have a hydroxyl group.
Minimum Inhibitory Concentrations (MICs)
The minimum inhibitory concentrations (MICs) of compounds 2–7 were determined
for each antimicrobial agent by using agar diffusion method. The inhibition zone was
measured in triplicates in four different concentrations (10–1000 µg/mL) and the mean
value standard deviation (SD) is recorded in Table S2 (Supplemental Materials).
Table S2 showed that compound 6 was the most active compound against all or-
ganisms except for C. albicans and showed the lowest MIC value (10 µg/mL). On the
other hand, compound 3 was found to be the least effective compound and showed the
highest MIC value (1000 µg/mL). The activities of other compounds can be arranged in
the following order: 2 > 5 > 7 > 4.
CONCLUSIONS
A series of diphenyl (4ꢁ-(aryldiazenyl)biphenyl-4-ylamino)(pyridin-3-yl)methyl-
phosphonates were synthesized and their antimicrobial activities were investigated.
Some of the synthesized compounds exhibit a remarkable inhibition of the growth of
gram-positive bacteria and gram-negative bacteria and fungi at low concentrations.
Experimental
Melting point determinations were performed by the open capillary method using
an Electrothermal MEL–TEMP II apparatus and are reported uncorrected. IR spectra were
recorded on a Perkin–Elmer 1430 Spectrophotometer using KBr disc technique. 1H NMR
spectra were recorded on a Bruker AC400 spectrometer operating at 400 MHz. The spectra

ANTIMICROBIAL ACTIVITIES OF α-AMINOPHOSPHONATES
1205
were recorded in DMSO–d6. Chemical shifts δ are reported in parts per million (ppm) rela-
tive to TMS and coupling constants J are in Hz and have been rounded to the nearest whole
number. EI mass spectra were recorded at energy 70 eV with a 7070 EQ mass spectrometer.
Microanalysis was performed by analytical service at Cairo and Tanta Universities, Egypt.
Reagents and solvents were used from commercial sources without purification.
Chemistry
Synthesis of Diphenyl (4ꢀ-Aminobiphenyl-4-Ylamino)(Pyridin-3-yl-)
Methylphosphonate (1). A mixture of pyridine-3-carboxaldehyde (1.07 g, 10 mmol),
benzidine (1.84 g, 10 mmol), triphenylphosphite (3.72 g, 12 mmol), and titanium
tetrachloride (0.19 g, 1 mmol) in dichloromethane (10 mL) was stirred at room temperature
for 26 h. The solvent was removed under reduced pressure and the residue obtained was
treated with methanol (20 mL) and then filtered to remove the solid materials. A mixture
of water (10 mL) and dichloromethane (10 mL) was added to the filtrate. The organic
layer was separated and washed with water (10 mL), dried over anhydrous Na2SO4 and
removed under reduced pressure to give the crude product, which was recrystallized from
ethanol to give pure 1.
Yield 88%; colorless; mp 120–122 ◦C; IR (KBr): Selected IR data (KBr) νmax: 3329
(NH), 1597 (C N), 1322 (P O) and 823 (P O C) cm−1. 1H NMR (400 MHz, DMSO-d6)
δ (ppm) 10.17 (br s, exch., 1H, NH), 9.15–6.76 (m, 22H, aromatic), 5.16 (d, J = 16 Hz,
1H, CH) and 3.97 (s, exch., 2H, NH2). MS, m/z (%): 507 (M+, 5), 449 (12), 390 (22), 314
(35), 265 (44), 396 (5), 225 (100), 214 (12), and 168 (11). Anal calcd for C30H26N3O3P
(507.52): C, 71.00; H, 5.16; N, 8.28; P, 6.10; Found: C, 71.12; H, 4.94; N, 8.01; P, 6.15%.
General Procedure for the Synthesis of Diphenyl (4ꢀ-(Aryldiazenyl)Biph-
enyl-4-Ylamino)(Pyridin-3-yl)Methylphosphonates 2–7. A cold (0 ◦C) solution of
◦
sodium nitrate (0.76 g, 11 mmol) in H2O (10 mL) was added gradually to a cold (0 C)
suspension of 1 (5.07 g, 10 mmol) in conc. HCl (5◦mL). The diazonium salt thus obtained
was added with continuous stirring to a cold (0 C) solution of coupler (10 mmol) in
aqueous NaOH solution (10%; 15 mL). The mixture was stirred at 0 ◦C for 30 min and the
dye obtained was filtered, washed with H2O, dried and crystallized from ethanol to give
pure 2–7. The physical properties of products 2–7 are recorded in Table 1.
Diphenyl (4ꢁ-((4-hydroxynaphthalen-1-yl)diazenyl)biphenyl-4-ylamino)(pyri-
din-3-yl)methylphosphonate (2): Selected IR data (KBr) νmax: 3494 (OH/NH), 1613
1
(C N), 1581 (N N), 1323 (P O) and 893 (P O C) cm−1. H NMR (400 MHz,
DMSO-d6) δ (ppm) 9.10 (s, exch., 1H, OH), 8.73 (br s, exch., 1H, NH), 8.50–7.21 (m,
28H, H-arom) and 6.95 (d, J = 12 Hz, 1H, CH). MS, m/z (%): 662 (M+, 3), 613 (2),
531 (3), 439 (59), 410 (4), 396 (5), 362 (29), 273 (12), and 98 (100). Anal. Calcd. for
C40H31N4O4P (662.67): C, 72.50; H, 4.72; N, 8.45; P, 4.67; Found: C, 72.62; H, 4.74; N,
8.41; P, 4.65%.
Diphenyl (4ꢁ-((2-hydroxynaphthalen-1-yl)diazenyl)biphenyl-4-ylamino)(pyri-
din-3-yl)methylphosphonate (3): Selected IR data (KBr) νmax: 3337(OH/NH), 1613
1
(C N), 1580 (N N), 1325 (P O), and 890 (P O C) cm−1. H–NMR (400 MHz,
DMSO–d6) δ (ppm): 9.09 (s, exch., 1H, OH), 8.81 (br s, exch., 1H, NH), 8.72–7.43 (m,
28H, H-arom) and 6.95 (d, J = 12 Hz, 1H, CH). MS, m/z (%): 662 (M+, 4), 613 (4),
531 (6), 439 (66), 410 (6), 396 (4), 362 (32), 273 (15) and 98 (100). Anal. Calcd. for
C40H31N4O4P (662.67): C, 72.50; H, 4.72; N, 8.45; P, 4.67; Found: C, 72.60; H, 4.77; N,
8.39; P, 4.69%.

1206
M. F. ABDEL-MEGEED ET AL.
Diphenyl (4ꢁ-((2,4-dihydroxyphenyl)diazenyl)biphenyl-4-ylamino)(pyridin-3-
yl)methylphosphonate (4): Selected IR data (KBr) νmax: 3332 (OH/NH), 1610 (C N),
1
1490 (N N), 1320 (P O), and 896 (P O C) cm−1. H NMR (400 MHz, DMSO-d6)
δ (ppm) 9.11 (s, exch., 1H, OH), 8.81 (br s, exch., 1H, NH), 8.73 (s, exch., 1H, OH),
8.50–7.08 (m, 25H, H-arom) and 6.92 (d, J = 13 Hz, 1H, CH). MS, m/z (%): 628 (M+, 3),
564 (4), 514 (3), 436 (25), 362 (100), 282 (28) and 273 (12). Anal. Calcd. for C36H29N4O5P
(628.61): C, 68.78; H, 4.65; N, 8.91; P, 4.93; Found: C, 68.62; H, 4.84; N, 8.86; P, 4.95%.
Diphenyl (4ꢁ-((5-amino-2-hydroxyphenyl)diazenyl)biphenyl-4-ylamino)(pyri-
din-3-yl)methylphosphonate (5): Selected IR data (KBr) νmax: 3399 (OH/NH), 1613
1
(C N), 1582 (N N), 1327 (P O), and 884 (P O C) cm−1. H–NMR (400 MHz,
DMSO–d6) δ (ppm): 9.09 (s, exch., 1H, OH), 8.81 (br s, exch., 1H, NH), 8.72–6.93 (m,
25H, H-arom), 6.63 (d, J = 13 Hz, 1H, CH) and 6.37 (s, exch., 2H, NH2). MS, m/z
(%): 627 (M+, 3), 413 (2), 362 (100), 282 (38), 273 (13) and 152 (38). Anal. Calcd. for
C36H30N5O4P (627.63): C, 68.89; H, 4.82; N, 11.16; P, 4.94; Found: C, 68.62; H, 4.94; N,
11.01; P, 4.85%.
7-Amino-3-((4ꢁ-((diphenoxyphosphoryl)(pyridin-3-yl)methylamino)biphenyl-4-
yl)diazenyl)-4-hydroxynaphthalene-2-sulfonic acid (6): Selected IR data (KBr) νmax
:
.
3424 (OH/NH), 1615 (C N), 1519 (N N), 1299 (P O), and 892 (P O C) cm−1
1H–NMR (400 MHz, DMSO–d6) δ (ppm): 9.09 (s, exch., 1H, OH), 8.90 (s, exch., 1H,
SO3H), 8.80 (br s, 1H, NH), 8.72–6.93 (m, 26H, H-arom), 6.75 (d, J = 12 Hz, 1H, CH)
and 6.83 (s, exch., 2H, NH2); MS, m/z (%): 757 (M+, 6), 515 (39), 439 (15), 362 (72), 282
(100) and 273 (11). Anal. Calcd. for C40H32N5O7PS (757.75): C, 63.40; H, 4.26; N, 9.24;
P, 4.09; Found: C, 63.62; H, 4.24; N, 9.21; P, 4.15%.
Diphenyl (4ꢁ-((2-amino-5-methylphenyl)diazenyl)biphenyl-4-ylamino)(pyridin-
3-yl)methylphosphonate (7): Selected IR data (KBr) νmax: 3408 (OH/NH), 1612 (C N),
1582 (N N), 1323 (P O), and 890 (P O C) cm−1. 1H–NMR (400 MHz, DMSO–d6) δ
(ppm): 9.09 (br s, exch., 1H, NH), 8.80–6.49 (m, 25H, H-arom), 5.65 (d, J = 12 Hz, 1H,
CH), 5.26 (s, exch., 2H, NH2) and 2.30 (s, 3H, CH3). MS, m/z (%): 625 (M+, 9), 442 (15),
362 (100), 282 (97), 273 (40) and 152 (95). Anal. Calcd. for C37H32N5O3P (625.65): C,
71.03; H, 5.16; N, 11.19; P, 4.95; Found: C, 71.02; H, 5.04; N, 11.01; P, 4.85%.
Biological Assay
Bacteria. After gram-staining procedure, gram-negative cells appear pink. The
gram-negative bacterium used in this study was E. coli, which is known as the back-
bone example for gram-negative bacteria and cause urinary infection, wound infection, and
gastroenteritis. The thick cell wall of a gram-positive organism retains the crystal violet
dye used in the gram-staining procedure, so the stained cells appear purple under magnifi-
cation. Gram-positive bacteria used in this study were B. subtilis and S. aureus. B. subtilis
is mostly involved in Urinary infection, wound, ulceration, and septicemia. S. aureus is the
mild stone of gram-positive bacteria and it is a causative agent of pneumonia, meningitis,
and food poisoning.
Fungi. Pathogenic fungi spatially yeasts are responsible for a number of diseases
in human and animals. A number of pathogenic strains of fungi are represented in C.
albicans and S. cerevisiae. The tested organisms were obtained from the culture collection
of Bacteriology Unit, Department of Botany, Faculty of Science, Tanta University, Egypt.
Media Used and Antimicrobial Assay. Compounds that produced the highest
inhibition zones were selected and assayed further at different concentrations in suspensions

ANTIMICROBIAL ACTIVITIES OF α-AMINOPHOSPHONATES
1207
to quantify their inhibitory effects. Nutrient and Sabouraud’s broths were used in activation
of organisms.33
Determination of Minimum Inhibitory Concentrations (MICs). The antimi-
crobial activities of the tested samples were determined by measuring the diameter of zone
of inhibition expressed in millimeter. The inhibition zones were measured in triplicates and
expressed as mean SD.34
REFERENCES
1. Ordo´n˜ez, M.; Rojas-Cabrera, H.; Cativiela, C. Tetrahedron 2009, 65, 17-49.
2. Calde´s, C.; Vilanova, B.; Adrover, M.; Mun˜oz, F.; Donoso, J. Bioorg. Med. Chem. 2011, 19,
4536-4543.
3. El Sayed, I.; El Kosy, S. M.; Hawata, M. A.; El Gokha, A. A.-A.; Tolan, A.; Abd El-Sattar, M.
M. J. Am. Sci. 2011, 7, 357-361.
4. Kafarski, P.; Lejczak, B. Phosphorous, Sulfur, Silicon 1991, 63, 193-215.
5. Allen, M. C.; Fuhrer, W.; Tuck, B.; Wade, R.; Wood, J. M. J. Med. Chem. 1989, 32, 1652-1661.
6. Giannousis, P. P.; Bartlett, P. A. J. Med. Chem. 1987, 30, 1603-1609.
7. Atherton, F. R.; Hassall, C. H.; Lambert, R. W. J. Med. Chem. 1986, 29, 29-40.
8. Natchev, I. A. Liebigs Ann. Chem. 1988, 861-867.
9. Hirschmann, R.; Smith, A. B.; Taylor, C. M.; Benkovic, P. A.; Taylor, S. D.; Yager, K. M.;
Sprengeler, P. A.; Benkovic, S. J. Science 1994, 265, 234-237.
10. Qian, C.; Huang, T. J. Org. Chem. 1998, 63, 4125-4128.
11. Ranu, B. C.; Hajra, A.; Jana, U. Org. Lett. 1999, 1, 1141-1143.
12. Manabe, K.; Kobayashi, S. Chem. Commun. 2000, 669-670.
13. Chandrasekhar, S.; Prakash, S. J.; Jagadeshwar, V.; Narsihmulu, Ch. Tetrahedron Lett. 2001, 42,
5561-5563.
14. Ghosh, R.; Maiti, S.; Chakraborty, A.; Maiti, D. K. J. Mol. Catal. A: Chem. 2004, 210, 53-57.
15. Xu, F.; Luo, Y.; Deng, M.; Shen, Q. Eur. J. Org. Chem. 2003, 4728-4730.
16. Manjula, A.; Rao, B.; Neelakantan, P. Synth. Commun. 2003, 33, 2963-2969.
17. Smith, K.; El-Hiti, G. A.; Abdo, M. A.; Abdel-Megeed, M. F. J. Chem. Soc., Perkin Trans. 1
1995, 1029-1033.
18. Smith, K.; El-Hiti, G. A.; Abdel-Megeed, M. F.; Abdo, M. A. J. Org. Chem. 1996, 61, 647-655.
19. Smith, K.; El-Hiti, G. A.; Abdel-Megeed, M. F.; Abdo, M. A. J. Org. Chem. 1996, 61, 656-661.
20. Smith, K.; El-Hiti, G. A.; Hawes, A. C. Synthesis 2003, 2047-2052.
21. Smith, K.; El-Hiti, G. A.; Mahgoub, S. A. Synthesis 2003, 2345-2348.
22. El-Hiti, G. A. Synthesis 2003, 2799-2804.
23. El-Hiti, G. A. Synthesis 2004, 363-368.
24. Smith, K.; El-Hiti, G. A.; Abdel-Megeed, M. F. Synthesis 2004, 2121-2130.
25. Smith, K.; El-Hiti, G. A.; Hegazy, A. S. Synthesis 2005, 2951-2961.
26. Smith, K.; El-Hiti, G. A.; Hegazy, A. S. Synlett 2009, 2242-2244.
27. Smith, K.; El-Hiti, G. A.; Hegazy, A. S. Synthesis 2010, 1371-1380.
28. Smith, K.; El-Hiti, G. A.; Hegazy, A. S.; Fekri, A. Heterocycles 2010, 80, 941-956.
29. Smith, K.; El-Hiti, G. A.; Hegazy, A. S. Chem. Commun. 2010, 46, 2790-2792.
30. Smith, K.; El-Hiti, G. A.; Hegazy, A. S.; Kariuki, B. Beilstein J. Org. Chem. 2011, 7, 1219-1227.
31. Browne, K. A.; Deheyn, D. D.; El-Hiti, G. A.; Smith, K.; Weeks, I. J. Am. Chem. Soc. 2011, 133,
14637-14648.
32. Abdel-Megeed, M. F.; Azaam, M. M.; El-Hiti, G. A. Monatsh. Chem. 2007, 138, 153-156.
33. Pridham, T. G.; Lindenfelser, L. A.; Shotwell, O. L.; Stodola, F.; Benedict, R. G.; Foley, C.; Jacks,
P. W.; Zaumeeyer, W. J.; Perston, W. H.; Mitchell, J. W. Phytopathology 1956, 46, 568-575.
34. Hsueh, P. R.; Chang, J. C.; Teng, L. J.; Yang, P. C.; Ho, S. W.; Hsieh, W. C.; Luh, K. T. J. Clin.
Microbiol. 1997, 35, 1021-1023.