Thioesters for the in vitro evaluation of agents to image brain cholinesterases

Figures & data

Table 1.  Affinity constants (K_m) and maximum velocity values (V_max) for N-methylpiperidinyl alkyl thioesters, N-methylpiperidinyl aryl esters and corresponding thioesters with butyrylcholinesterase (BuChE) and acetylcholinesterase (AChE). None of the aryl compounds (1–6) were hydrolyzed by AChE under the conditions used (X).

Compound	Structure	AChE		BuChE
		Km (µM)	Vmax (µM min^−1)	Km (µM)	Vmax (µM min^−1)
1		X	X	438 ± 75	45.0 ± 6.6
2		X	X	284 ± 28	24.7 ± 2.0
3		X	X	123 ± 42	21.0 ± 5.1
4		X	X	167 ± 17	30.7 ± 2.4
5		X	X	173 ± 13	27.6 ± 1.7
6		X	X	11 ± 1	9.7 ± 0.3
7		751 ± 26	18.3 ± 0.2	684 ± 54	16.7 ± 1.3
8		1108 ± 106	21.4 ± 2.2	302 ± 2	20.7 ± 0.1
9		X	X	129 ± 12	7.0 ± 0.3

Figure 1.  Repetitive absorbance scans for N-methylpiperidin-4-yl 4-cyanobenzoate in the presence of butyrylcholinesterase (BuChE) or acetylcholinesterase (AChE). Note change in absorbance over time when the compound was incubated with BuChE (left) reflecting hydrolysis of the compound by this enzyme. No change in absorbance with AChE (right) indicates no hydrolysis by this enzyme. The absorbance was measured every 2 min for 30 min.

Scheme 1.  Reaction scheme for the synthesis of (a) alkyl and aryl thioesters and (b) aryl esters.

Figure 2.  Histochemical staining of human brain tissue at the level of the thalamus in the coronal plane. (A) Parcellation of the thalamus in the region used to compare histochemical staining by various cholinesterase substrates; (B) Acetylthiocholine. (C) (N-methylpiperidin-4-yl) ethanethioate. Note that both of these substrates produced a similar pattern of staining recapitulating the known distribution of acetylcholinesterase in this region. (D) Butyrylthiocholine. (E) (N-methylpiperidin-4-yl) butanethioate. (F) (N-methylpiperidin-4-yl) 4-cyanobenzenecarbothioate. Note that these substrates produced a similar pattern of distribution that reflected the known distribution of butyrylcholinesterase in this region. AV: anteroventral nucleus; CL: central lateral nucleus; MD: mediodorsal nucleus; R: reticular nucleus; V: ventral nuclei. Scale bar = 200 µm.