The anticancer drug carboplatin
[Pt(cbdca-O,Oâ²)(NH
3
)
2
]
which contains the chelated dicarboxylate ligand cbdca,
cyclobutane-1,1-dicarboxylate, may be activated in vivo by
reaction with sulfur ligands. The reactions between the analogue
[Pt(en)(Me-Mal-O,Oâ²)] 1
(en = ethane-1,2-diamine,
Me-Mal = 2-methylmalonate) and the methionine derivatives
N-acetyl-L-methionine (Ac-Met),
glycyl-L-methionine (Gly-Met) and
L-methionylglycine (Met-Gly) have been studied at pH 7 and 4,
310 K, using
1
H and two-dimensional [
1
H,
15
N] heteronuclear single quantum coherence NMR spectroscopy
and HPLC. The ring-opened species
[Pt(en)(Me-Mal-O)(L-S)] (L = Ac-Met,
Gly-Met or Met-Gly) containing monodentate malonate and S-bound
monodentate methionine ligands were predominant in solution after 2 h.
The second-order rate constant for the ring-opening reaction of
1 with Ac-Met at pH 6.56 was determined to be
(1.48 ± 0.03) à 10
-
1
s
-1
M
-1
, and was similar for
reactions with Gly-Met. Methylmalonate α-CH deuteriation
rates were determined to be free Me-Met > ring-opened
complex 1. Molecular-mechanics modelling
suggested that hydrogen bonding between the free carboxylate group of
monodentate Me-Mal and the co-ordinated amine groups, and between the two
ring-opened ligands may contribute to the stability of the mixed-ligand
adducts. However, in the case of Met-Gly, the ring-opening rate
[(5.26 ± 0.10) à 10
-2
s
-1
M
-1
] was nearly
three times slower than that for the reaction of 1 with Ac-Met.
In contrast, the ring-closure rate of
[Pt(en)(Me-Mal-O)(Met-Gly-S)]
[k
1
= (1.37 ±
0.03) Ã 10
-4
s
-1
]
to give the S,N-chelated adduct was faster than that
of [Pt(en)(Me-Mal-O)(Ac-Met-S)]
-
2
[(2.27 ± 0.04) à 10
-5
s
-1
]. The S,N-chelated
adducts [Pt(en)(Ac-MetH
-1
-S,N)]
3,
[Pt(en)(Gly-MetH
-1
-S,N)]
+
and
[Pt(en)(Met-GlyH
-1
-S,N)]
+
became the predominant products of the reactions after about 24 h.
Ring-opened adducts of chelated dicarboxylate platinum anticancer
complexes with methionine derivatives could play a significant role in
their mechanism of action.
抗癌药物
卡铂[Pt(cbdca-O,O')(NH_3)_2],其中包含螯合的二
羧酸配体cbdca(
环丁烷-1,1-二
羧酸盐),可能通过与
硫配体的反应在体内被激活。对类似物[Pt(en)(Me-Mal-O,O')]1(en =
乙烷-1,2-二胺,Me-Mal = 2-
甲基丙二酸)与蛋
氨酸衍
生物N-乙酰-L-蛋氨酸(Ac-Met)、
甘氨酰-L-蛋氨酸(Gly-Met)和L-蛋
氨酰甘
氨酸(Met-Gly)在pH 7和4,310 K下进行的反应进行了研究,使用了^1H和二维[^1H, ^15N]异核单量子相干NMR谱和HPLC。环开型物种[Pt(en)(Me-Mal-O)(L-S)](L = Ac-Met、Gly-Met或Met-Gly),包含单齿
丙二酸和S-结合单齿蛋
氨酸
配体,在2小时后成为溶液中的主要物种。环开反应的二级速率常数在pH 6.56下以1与Ac-Met的反应确定为(1.48 ± 0.03)× 10^-1 s^-1 M^-1,与Gly-Met的反应类似。
甲基丙二酸α-CH
氘化速率确定为自由Me-Met > 环开复合物1。分子力学建模表明,单齿Me-Mal的自由
羧酸基团与配位胺基团之间的氢键,以及两个环开
配体之间可能有助于混合
配体加合物的稳定性。然而,对于Met-Gly,环开速率[(5.26 ± 0.10) × 10^-2 s^-1 M^-1]几乎比1与Ac-Met的反应慢三倍。相反,[Pt(en)(Me-Mal-O)(Met-Gly-S)]的环闭速率[k1 = (1.37 ± 0.03) × 10^-4 s^-1]比[Pt(en)(Me-Mal-O)(Ac-Met-S)]-2[(2.27 ± 0.04) × 10^-5 s^-1]快。S,N-螯合加合物[Pt(en)(Ac-MetH-1-S,N)]3、[Pt(en)(Gly-MetH-1-S,N)]+和[Pt(en)(Met-GlyH-1-S,N)]+在约24小时后成为反应的主要产物。螯合二
羧酸铂抗癌复合物与蛋
氨酸衍
生物的环开加合物可能在它们的作用机制中发挥重要作用。