酸触媒によるdAMP水解の移行状態分析
1Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4M1, Canada.
Journal of the American Chemical Society
|May 15, 2007
まとめ
この研究は,デオキシアデノシンモノフォスファート水解中にデオキシリボースオキサカルベニウムイオンの中間物質の最初の直接的な証拠を提供します. 動的同位体効果は段階的なメカニズムを明らかにし,反応経路と移行状態の構造を明確にします.
科学分野:
- バイオケミストリー バイオケミストリー
- 有機化学 オーガニック・ケミストリー
- 物理化学 物理化学
背景:
- デオキシアデノシンモノフォスファート (dAMP) の水解機構を理解することは,DNAの安定性と修復を理解するために極めて重要です.
- 以前の研究では,dAMPの水解における重要な中間物質の直接的な証拠が欠け,移行状態の構造と反応性は不確実であった.
研究 の 目的:
- デオキシアデノシンモノフォスファート (dAMP) 水解の移行状態 (TS) 構造と固有の反応性を解明する.
- 溶液中のデオキシリボシルオキサカルベニウムイオンの中間体に対する最初の直接的な実験的証拠を提供すること.
主な方法:
- 0.1M HCl.でdAMPの水解に多重運動同位体効果 (KIEs) を利用した.
- 50%メタノール/0.1 M HClを使用し,製品の分布 (デオキシリボゼ5フォスファートおよびメチルdRMPイソマー) を分析した.
- ハイブリッド密度関数理論の計算を行い,さまざまな反応機構の計算移行状態を決定しました.
主要な成果:
- 実験的なKIEsは,離散型デオキシリボシルオキサカルベニウムイオンの中間体を含む段階的な (SN1) 機構を確認しました.
- 製品分析では,α-β-メチルdRMPの8.5:1比を示し,反応の80%がコンタクトイオンペア,20%が溶媒で分離されたイオンペアまたは自由イオン経由で進行することを示唆しました.
- 計算データと実験データでは,20%がDN+ANメカニズムを通過し,80%がDN*ANメカニズムを通過し,C-Nボンド・クリヴァージは逆行可能であることを説明する際に,優れた一致を示した.
結論:
- この研究は,dAMPの水解中に溶液中のデオキシリボシルオキサカルベニウムイオンの中間体に対する最初の直接的な証拠を提供します.
- 反応は主にコンタクトイオンペア (DN*ANメカニズム) を介して進行し,可逆的なC-N結合の割れに続いて,オキサカルベニウムイオンに対する不可逆的な水攻撃が続く.
- 計算された1−14C KIEは,アデニンプロトネーション状態に対して非常に敏感であり,移行状態の詳細な探査を提供します.
関連する概念動画
02:45Acid-Catalyzed Hydration of Alkenes
Alkenes react with water in the presence of an acid to form an alcohol. In the absence of acid, hydration of alkenes does not occur at a significant rate, and the acid is not consumed in the reaction. Therefore, alkene hydration is an acid-catalyzed reaction.
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
02:35Acid-Catalyzed Dehydration of Alcohols to Alkenes
In a dehydration reaction, a hydroxyl group in an alcohol is eliminated along with the hydrogen from an adjacent carbon. Here, the products are an alkene and a molecule of water. Dehydration of alcohols is generally achieved by heating in the presence of an acid catalyst. While the dehydration of primary alcohols requires high temperatures and acid concentrations, secondary and tertiary alcohols can lose a water molecule under relatively mild conditions.
01:01Acid Halides to Carboxylic Acids: Hydrolysis
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
01:13Esters to Carboxylic Acids: Acid-Catalyzed Hydrolysis
Hydrolysis of esters under acidic conditions proceeds through a nucleophilic acyl substitution. In the presence of excess water, the reaction proceeds in a reversible manner, forming carboxylic acids and alcohols.
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
01:28Amides to Carboxylic Acids: Hydrolysis
Amides can undergo either acid-catalyzed hydrolysis or base-promoted hydrolysis through a typical nucleophilic acyl substitution. Each hydrolysis requires severe conditions.
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...