N-琥珀酰-5-氨基-4-羧基咪唑核苷酸（SACAIR）

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\usepackage{chemfig}
\begin{document}

\chemfig{
	\fbox{R}-[2,0.8]N(-[2,0.25]9)
	-[3.5,0.6](-[3.3,0.25]4)(-[4.5,0.7]N(-[2,0.25]3)(-[4,0.3]H_2))
	=[2,0.8](-[4.8,0.25]5)(-[3,0.7](=[2,0.7]O)
	(
		-[4,0.8]NH_2
			-[4,0.5]C
				(-[4,0.25]H)
				(-[6,0.5]COOH)
				(-[2,0.5]C
					(-[,0.3]H_2)
					(-[2,0.5]COOH)
				)
	)
	(-[6,0.25]6))
	-[0.5,0.8]N(-[5.5,0.25]7)(-[,0.3]H)
	=[6.55,0.8]
		(-[4,0.2]8)
		-[5.25,0.6]
}

\end{document}

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\usepackage{chemfig}
\begin{document}

\chemfig{
(-[3.3,0.25]4)(-[4.5,0.7]N-[3,0.25]3)
=[2,0.8]
	(-[4.8,0.25]5)
	(
		-[3,0.7]C
			(=[2,0.7]O)
			(-[6,0.25]6)
			(-[4.7,0.8]N(-[3,0.25]1)
			)
	)
	(
		-[0.5,0.8]N(-[5.5,0.25]7)
		=[6.55,0.8](-[4,0.25]8)
		-[5.25,0.8]N(-[2,0.25]9)(-[6,0.8]\fbox{R})
		-[3.5,0.6]
	)
}

\end{document}