Synthesis and DNA Cleavage Activity of Bis‐3‐chloropiperidines as Alkylating Agents

Abstract

Nitrogen mustards are an important class of bifunctional alkylating agents routinely used in chemotherapy. They react with DNA as electrophiles through the formation of highly reactive aziridinium ion intermediates. The antibiotic 593A, with potential antitumor activity, can be considered a naturally occurring piperidine mustard containing a unique 3-chloropiperidine ring. However, the total synthesis of this antibiotic proved to be rather challenging. With the aim of designing simplified analogues of this natural product, we developed an efficient bidirectional synthetic route to bis-3-chloropiperidines joined by flexible, conformationally restricted, or rigid diamine linkers. The key step involves an iodide-catalyzed double cyclization of unsaturated bis-N-chloroamines to simultaneously generate both piperidine rings. Herein we describe the synthesis and subsequent evaluation of a series of novel nitrogen-bridged bis-3-chloropiperidines, enabling the study of the impact of the linker structure on DNA alkylation properties. Our studies reveal that the synthesized compounds possess DNA alkylating abilities and induce strand cleavage, with a strong preference for guanine residues.

Bis-3-chloropiperidines containing bridging lysine linkers: Influence of side chain structure on DNA alkylating activity

“…These observations, and the rapid formation of the reactive species followed by the nucleophilic attack of water, are in good correlation with our hypothesis and with studies on DNA reactivity shown here and in previous paper. 14 Consequently, the present investigations are further supporting our proposed mechanism of reaction. While more work is needed to determine the reactivity in complex biological conditions reflecting in vivo environment, the current studies serve as an experimental model system to demonstrate the efficacy of bis-3-chloropiperidines as DNA alkylating agents.…”

“…These data are consistent with our findings in recently published DNA cleavage studies employing a different plasmid (pAT153). 14 Figure 2b and c show the agarose gel electrophoresis pattern for the novel lysine-bridged bis-3-chloropiperidines 1-6. Compounds 1-3 generated single-strand nicks in supercoiled DNA, whereas 4 showed no significant effect (Fig.…”

“…In addition, investigations of linker structure on DNA alkylation activity revealed that the flexibility of the linker is important for alkylation efficiency, whereas the direct introduction of an aromatic group as linker leads to a decrease in activity. 14 Due to our experimental observations it appeared promising to attempt the synthesis of novel bis-3-chloropiperidines containing a flexible linker which offers the possibility of placing the aromatic moiety in the side chain (1-6, Fig. 1c).…”

“…1b), which can be considered as piperidine-based analogues of nitrogen mustards, are more reactive towards DNA than chlorambucil. 14 These new alkylating agents induce highly efficient cleavage in double-stranded DNA with dominating preference for guanine sites. In addition, investigations of linker structure on DNA alkylation activity revealed that the flexibility of the linker is important for alkylation efficiency, whereas the direct introduction of an aromatic group as linker leads to a decrease in activity.…”

“…2a). 14 The amino acid L-lysine 7 is a suitable linker structure for the preparation of a new set of bis-3-chloropiperidines. The carboxylic acid functionality of lysine provides a position at which the side chain can be modified.…”