Biomedical Engineering Reference
In-Depth Information
O
O
O
O
C CH
2
OC(CH
2
)y C
O CH
2
C
HN
CH CO D
O C
CH
R
NH
n
O
O
R
R = CH
2
CH(CH
3
)
2
, CH
2
C
6
H
5
; D = (CH
2
)
8
, (CH
2
)
12
; y = 4, 8.
Figure 5.8
AA-BB PDPs composed of glycolic acid,
α
- AAs, and dicarboxylic acids.
CO
(CH
2
)y
CO NH
CH CO
ODO
CO
CH NH
n
H
N
H
N
C
C
.
NH
.
H
2
N
TosOH
HN
NH
2
HOsoT
y = 2, 4, 8; D = (CH
2
)
3
, (CH
2
)
4
, (CH
2
)
6
Figure 5.9
Arginine - based cationic ABBPs - PEAs.
unit, and showed increased biodegradation rates. Additionally, the enhanced
hydrolysis of polysuccinates is linked with intramolecular catalysis (see Ref. [56]
and references cited therein).
Poly(depsipeptide)s (PDPs)
. Very recently [21, 43] a new class of nonfunctional
AABBPs - AA - BB - type PDPs - were obtained by AP of TAADs with active di -
p
- ni-
trophenyl esters of
O
,
O
- diacyl - bis - glycolic acids (Scheme 5.2 ) and have the general
structure given in Figure 5.8 .
PDPs also have two additional and highly polarized (close by nature to the ester
bonds in poly(glycolic acid)) ester bonds (in total four ester bonds) as compared
with regular PEAs above, containing two ester bonds per elemental links, and
hence showed increased biodegradation rates.
Functional PEAs. Polyacids.
Katsarava and Chu [15, 16] synthesized functional
co
-PEAs containing a variable amount of lateral carboxyl groups, applying di-
TosOH salt of l-lysine benzyl ester as a comonomer. The goal
co
- PEAs were
obtained by selective catalytic hydrogenolysis (debenzylation) of benzyl ester pre-
polymer using Pd catalyst. Free lateral COOH groups can be used for numerous
chemical transformations and
co -
PEAs are suitable drug carriers that will be dis-
cussed below. It has to be noted that lysine has parallel orientation (Figure 5.2),
whereas other amino acids' orientation is adirectional, that is, in whole
′
α
- AAs '
orientation in this types of polymers is mixed.
Polycations.
Arginine - based TAADs are tetra -
TosOH
salts that act as bifunctional
nucleophilic monomer (via two
-amino groups). This allows to synthesize the
linear and soluble polycationic PEAs (Figure 5.9) by AP of l - arginine - based TAADs
with di-
p
- nitrophenyl esters of
α
- alkylenedicarboxylic acids [33 - 35] .
The arginine -based PEA composed of succinic acid and 1,3-propanediol (the less
hydrophobic one among the PEAs obtained) was water soluble at room tempera-
ture. Very recently Memanishvili
et al.
[35] obtained arginine - based poly(ether ester
amide)s, PEEAs, and poly(ether ester urethane)s, PEEURs, and poly(ether ester
α
,
ω
