149 Page 4 of 17
El-Nassan, ElMeshad, Wadie and Sayed (2018) 35:149
Chemical Synthesis
J = 7.2 Hz), 0.95 (t, 3H, J = 7.2 Hz), 1.27 (m, 24H), 1.41 (d,
3H, J = 7.2 Hz), 1.61–1.67 (p, 2H, J = 7.2 Hz), 2.20 (t, 2H,
Melting points (mp) were determined using Stuart SMP20
apparatus and were uncorrected. The FTIR spectra were re-
corded on Shimadzu IR 435 spectrophotometer and values
J = 7.6 Hz), 2.36 (t, 2H, J = 7.2 Hz), 4.23 (m, 4H), 4.58–4.65
(p, 1H, J = 7.2 Hz), 6.07 (br d, 1H, J = 7.2 Hz, D O ex-
2
1
3
changeable); C NMR (100 MHz, CDCl ) 13.6, 14.1, 18.7,
3
−
1
1
13
were represented in cm . The H NMR and C NMR
spectra were carried out on Bruker 400 MHz and 100MHz
spectrophotometer, respectively, Faculty of Pharmacy, Cairo
University, Cairo, Egypt. Tetramethylsilane (TMS) was used
as an internal standard and chemical shifts were recorded in
ppm on δ scale and coupling constants (J) were given in Hz.
Elemental analyses were carried out at the regional center for
mycology and biotechnology, Al-Azhar University, Cairo,
Egypt, using PerkinElmer PE 2400 CHN Elemental
Analyzer. Analytical thin layer chromatography (TLC) on sil-
ica gel plates containing UV indicator was employed routinely
to follow the course of the reactions and to check the purity of
products. All reagents and solvents were purified and dried by
standard techniques. Methyl N-palmitoyl L-alaninate (PAM)
and N-palmitoyl L-alanine (PA) were synthesized according to
the method reported by Pal et al. (13).
19.0, 22.6, 24.7, 25.6,29.0, 29.2, 29.3, 29.4, 29.5, 29.6, 29.6,
29.6, 30.5, 31.9, 33.8,36.6, 47.9, 65.3, 172.7, 173.4;Anal.
Calcd for C H NO : C, 72.01; H, 11.82; N, 3.65. Found:
2
3
45
3
C, 72.26; H, 11.69; N, 3.57.
N-n-Hexadecanoyl (L)-alanine; N-palmitoyl L-alanine (PA)
This compound was prepared by alkaline hydrolysis of methyl
N-palmitoyl L-alaninate (PAM) according to the method re-
ported by Pal et al. (13) Yield: 94%; mp: 92–93°C (reported
−1
91–93°C (13)); IR (cm ): 3321 (NH), 2954, 2848 (CH-ali-
1
phatic), 1701 (acid C=O), 1647 (amide C=O); H NMR
(400 MHz, CDCl ) 0.90 (t, 3H, J = 6.6 Hz), 1.27 (m, 24H),
3
1.41 (d, 3H, J = 6.6 Hz), 1.61–1.67 (p, 2H, J = 7.2 Hz), 2.35
(t, 2H, J = 7.5 Hz), 4.60 (br s, 1H), 6.12 (br s, 1H, D O ex-
2
1
3
changeable); C NMR (100 MHz, CDCl ) 14.1, 17.9, 22.6,
3
24.6, 25.5, 29.0, 29.2, 29.3, 29.4, 29.5, 29.5, 29.6, 29.6, 29.6,
General Procedure for the Synthesis of Alkyl N-palmitoyl
31.9, 33.9, 36.4, 179.0, 179.6.
L-alaninates:
Formation of Organogels
A mixture of methyl, ethyl or butyl L-alaninate HCl salts
(
10 mmol), triethylamine (2.02 g, 20 mmol) in methylene chlo-
The ability of the prepared organogelators (PAM, PAE, PAB
or PA) to gel in three injectable vegetable oils: safflower oil,
sesame oil and soybean oil was examined at four different
concentrations (1, 5, 7.5 and 10% w/v) and was investigated
using the inverted tube method. Briefly, an amount of each
gelator (10, 50, 75 and 100 mg) was weighed and placed into a
4 mL screw-capped vial, and then 1 mL of each oil was added.
The mixture was heated in a hot water bath to 50 °C to
dissolve the solid completely and then allowed to cool over-
night at room temperature. Gelation was confirmed when the
mixture did not flow upon inversion of the vial. The best
chosen gel formulations were loaded with granisetron. The
drug (10 mg) was dispersed in 1 mL oil using bath sonicator
(S30H Elmasonic, Elma Schmidbauer GmbH, Singen,
Germany) for 5 min. The gelator was added and the temper-
ature of the oil was raised to 50 °C till complete dissolution.
To boost the syringeability of granisetron organogel in case of
in vivo study, 10% v/v NMP was added and mixed till the gel
structure was completely lost.
ride (25 mL) was stirred at room temperature for 30 min.
Palmitoyl chloride (2.75 g, 10 mmol) was added dropwise
and the reaction mixture was stirred at room temperature
for 5 h then kept overnight. The solvent was concentrated
under reduced pressure, and the solid formed was filtered,
washed with water (50 mL) and saturated sodium carbonate
solution (50 mL), then dried and crystallized from ethanol.
N-n-Hexadecanoyl Ethyl (L)-alaninate; Ethyl N-palmitoyl L-
alaninate (PAE). Yield: 91%; mp: 61–62°C (reported 62°C
(
−
1
35)); IR (cm ): 3323 (NH), 2920, 2850 (CH-aliphatic),
1
1
741 (ester C=O), 1647 (amide C=O); H NMR
(400 MHz, CDCl ) 0.90 (t, 3H, J = 7.0 Hz), 1.27 (m, 24H),
3
1
.41 (d, 3H, J = 7.1 Hz), 1.61–1.68 (p, 2H, J = 7.2 Hz), 2.20
(t, 2H, J = 7.7 Hz), 2.36(t, 3H, J = 7.2 Hz),4.23 (q, 2H, J =
7
6
1
2
1
3
.2 Hz), 4.58–4.65 (p, 1H, J = 7.2 Hz), 6.09 (br d, 1H, J =
1
3
.4 Hz, D O exchangeable); C NMR (100MHz, CDCl )
2
3
4.1, 18.6, 22.6, 24.7, 25.6, 28.8,29.0, 29.2, 29.3, 29.4,
9.6, 29.6, 31.9, 33.9, 35.3, 36.6, 45.1, 47.9, 61.5, 172.8,
73.4;Anal. Calcd for C H NO : C, 70.94; H, 11.62; N,
Characterization of the Organogels
2
1
41
3
.94. Found: C, 70.86; H, 11.79; N, 4.05.
Critical Gelling Concentration
N-n-Hexadecanoyl Butyl (L)-alaninate; Butyl N-palmitoyl L-
−
1
alaninate (PAB). Yield: 93%; mp: 54–55°C; IR (cm ): 3325
The critical gelation concentration (CGC) was studied and
confirmed by the inverted tube method. Briefly, after the
weight of the organogelator needed to gel in the oil was
(
(
NH), 2956, 2848 (CH-aliphatic), 1739 (ester C=O), 1647
amide C=O); H NMR (400 MHz, CDCl ) 0.90 (t, 3H,
1
3