Chemistry Reference
In-Depth Information
The bulky triphenylmethyl moiety functions to block the 5
0
hydroxyl groups and is removed when
necessary. The same is true of the acetyl portion that also serves to block the 3
0
hydroxyl position.
The product can be used for further expansion of the chain.
Another approach to the syntheses of nucleic acids is to use polymeric supports as in the syntheses
of polypeptides. The preparation of protecting groups for attachment to carbon 5 of deoxyribose on
the surface of cross-linked polystyrene can be illustrated as follows [
57
]:
O
croslinked
postyrene
surface
OCH
3
OCH
3
OH
Cl
Another protective group that has been used is dimethoxy trityl. The carbon 3 of deoxyribose has
been protected with phosphoramide. Benzoyl groups are used to protect the adenine and guanine
bases. Lately, in place of cross-linked polystyrene, controlled pore glass supports have become
popular.
Commercial synthesizing machines are available today for polynucleotide syntheses. These are
similar to the synthesizers used in polypeptide syntheses.
8.7 Polyalkanoates
Many bacteria
are
a potential
source of naturally occurring polyesters, mainly
poly
(b-hydroxyalkanoate)s
with a general structure
CH
HO
CH
CH
2
C
O
CH
CH
2
C
O
CH
2
COOH
n
R
O
R
O
R
when the polymer is poly(
CH
3
[
69
]. The material is found in the form of
hard crystalline granules in many bacterial cells. The most common one, poly(
b
-hydroxybutyrate) R
¼
b
-hydroxybutyrate),
was discovered back in the 1920s and identified as a polymer of
D
-(
-hydroxybutyric acid. In the
native state this polymer may reach molecular weights of 1,000,000 or higher. It forms a compact
right-handed helix with a twofold screw axis and a repeat unit of 5.96
˚
. Because poly
(
)-
b
-position
makes it thermally unstable. This limits its use in plastics. It was found, however, that oxygen
starvation of bacterial cultures results in formation of a copolymer of
-hydroxybutyrate) is stereoregular, it is highly crystalline. The substitution in the
b
b
-hydroxybutyric acid with
b
-hydroxyvaleric acid instead of a homopolymer. Further investigations showed that as many as
11 different
b
-hydroxy acid constituents are present in different naturally occurring polyalkanoates,
depending upon the bacterial source and conditions of growth. Today, a family of products, marketed
b
