Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Nanosized Mg/Al-Hydrotalcites as Catalysts using Microwave Assisted Eco-Friendly for Rapid
Synthesis of Pyrazolo[1,5-a]Pyrimidine Derivatives
Mohamed Mokhtar 1 *, Sulaiman N. Basahel 1 , Islam H. Abd El-Maksod 1 , Tamer S.Saleh 2
1 Department of Chemistry, King Abdulaziz University, Jeddah80203, Saudi Arabia
2 Green Chemistry Department, National Research Centre, Dokki, Cairo, Egypt
Abstract-Synthetic nanosized Mg-Al-hydrotalcite is found to be a mild and efficient catalyst for the synthesis of Pyrazolo[1,5-a] Pyrimidine
derivatives in quantitative yields. Exclusive synthesis of Pyrazolo[1,5-a] Pyrimidine derivatives using Mg-Al-Hydrotalcite realized by
compatible basic sites of catalyst used. The present eco-friendly catalytic system is a potential alternative to soluble bases.
Py razo lo[1,5-a]Pyrimidine derivatives mo iety is a privileged
class of pharmacophore, as compounds bearing this structural
unit possess a broad spectrum of biological activities[1,2] they
have potent analgesic effects [3], also, pyrazolo[1,5-
a]pyrimidine derivative zaleplon is an ideal nonbenzodiazapine
sedative/hypnotic drug mainly used for
insomnia [4]. The various reported methodologies involve the
use of piperidine in ethanol under reflux for 8 hours [5], and
pyridine under reflux for 4 hours [6], or in drops of piperdine
under microwave irradiations [7]. Ho wever, these
methodologies have one or more disadvantages such as the use
of high boiling solvent, hazard solvent; also yield of reaction
O
+
NMe 2
R
1 2
2,4 R
a Me
b Ph
c p-OCH 3 Ph
NH 2
MW
N NH Catalyst
R
N
R
NH
2
3
1
N
H
N
Ph
3
NMe 2
O
-Me 2 NH
-H 2 O
N
4
N 7
Figure 1. Synthesis of Pyrazolo[1,5-a] Pyrimidine derivatives. (a)
One of the most stable structures of the Ti-C 60 complex where the Ti
atom (blue) is bonded to a double bond with four hydrogen molecules
attached (red). (b) The local structure of the Ti-C 60 double bond. (c)
Replacing the end carbon atoms shown in (b) by H results in an
ethylene molecule. This suggests that we may simply use the
ethylene molecule to hold Ti atoms, which then binds multiple
hydrogen molecules
4
5
Ph
6
not more than 70%. It is now widely accepted that there is an
urgent need for more environmentally acceptable processes in
the chemical industry [8]. Thus, use of heterogeneous solid
base catalysts instead of the classical homogeneous liquid base
catalysts makes separation of the product easier and produces
neither corrosion nor emulsion.
Layered double hydroxides (LDHs) or hydrotalcite like
materials (HTs) represent basis of new environment-friendly
technologies, involving cheaper and more efficient ways for
carrying out chemical reactions [9-11]. In this work, we
developed more benign effective methods for the synthesis of
derivatives of Pyrazolo[1,5-a]Pyrimidine for bio logical
screening purposes using nanosized Mg/Al hydrotalcite
(MgAl-HT) catalysts.
We first studied the effect of microwave irradiation on the
reaction in absence of catalysts then in the presenence of assynthesized
Mg/Al-HT (MgAl-HT-AS), hydrotalcites calcined
at 200 o C (MgAl-HT-200) , hydrotalcites calcined at 450 o C
(MgAl-HT-450), and their rehydrated forms (MgAl-HT-200-
RH and MgAl-HT-450-RH), respectively. We found no
reaction takes place in assistance of microwave irradiations
alone. The reaction carried out using MgAl-HT-AS catalyst
showed 92 % yield of the desired product in about 18 min.
The catalytic activity of the tested catalysts could be
summarized in the following manner: MgAl-HT-AS >MgAl-
Ht-200 > MgAl-HT-200-RH > MgAl-HT-450 > MgAl-HT-
450-RH.
We next discussed the effect of durability for the more
efficient catalyst by reusing the same catalyst five times,
taking the time to complete reaction as indication of catalytic
activity. The time taken to reach 100% conversion after five
time reusing the catalyst was 15, 20 and 21 min. for the 4a,4b
and 4c products, respectively.
In summary, one of the more promising classes of solid
bases is hydrotalcites, we have developed an efficient method
for synthesis of Pyrazolo[1,5-a]Pyrimidine derivatives by an
eco-friendly Mg/Al-HT catalyst, under microwave irradiation,
a significant high yield and short reaction time was observed
in using as-synthesized hydrotalcites than other activated
hydrotalcite catalysts.
This work was supported by Deanship of scientific Research
at King Abdulaziz University under Grant No. MS-104T536.
*Corresponding author: 1Tmmokhtar2000@yahoo.com
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6th Nanoscience and Nanotechnology Conference, zmir, 2010 306