Chemistry Reference
In-Depth Information
CH
3
H
3
C
N
h
ν
Ph
N
Ph
N
CH
3
CH
3
CH
3
CH
3
-
25
26
H
3
C
CH
3
N
SCHEME 3.13.
usually gave lower yields of adducts, but proceeded more rapidly than these azide
PAL agents. Finally, these data also indicate the difficulty in extrapolating the
effectiveness of a particular PAL agent from one type of biological substrate to
another.
Falvey has reviewed the chemistry of nitrenium ions and studied their chemistry
extensively via their photochemical generation from
N
-aminopyridinium salt
as
shown in Scheme 3.13.
77
Of particular relevance to this review is his characterization
of nitrenium ion reactivity with the common amino acids and readily accessible
proteins using transient spectroscopy (
25
4 ns, pumped at 355 nm).
78
The second-
>
26
order rate constants for nitrenium ion
in 10% aqueous acetonitrile are summarized
in Table 3.4. As might be expected, amino acids with carboxylic acid, amide, and
hydrocarbon side chains, including phenylalanine, were found to be unreactive. It is
rather surprising that the amino acids threonine and proline were also found to be
TABLE 3.4. Second-Order Rate Constants for the Reaction of Nitrenium Ion 26 with
Amino Acids and Standard Protein Molecules
Second-Order Rate
Constants
k
q
(M
1
s
1
)
Reactive
Amino Acids (%)
Amino Acid/Protein
Reactivity
(2.91
0.1)
10
9
L
-Tryptophan
High
(1.29
0.7)
10
9
L
-Methionine
High
(2.95
0.7)
10
8
L
-Tyrosine
High
(2.79
0.2)
10
8
L
-Cysteine
High
(8.04
1.6)
10
7
L
-Lysine
Moderate
(5.39
0.5)
10
7
L
-Histidine
Moderate
(3.04
0.5)
10
7
L
-Arginine
Moderate
(7.93
0.7)
10
6
L
-Serine
Low
Nonlinear about 2
10
8
at 0.02M glycine
Glycine
(7.71
0.8)
10
9
Chymotrypsin
High
9.9
(8.96
0.8)
10
8
Insulin
High
19.6
(8.22
0.9)
10
8
BSA (bovine serum albumin)
High
10.5
(5.79
0.6)
10
8
Lysozyme
High
14.7
(4.59
0.4)
10
8
BPR (bovine pancreatic
ribonuclease)
High
14.5
