Cholinesterase inhibitory triterpenoids from the bark of Garcinia hombroniana

Figures & data

Figure 1. Chemical structures of compounds 1–5.

Table 1. ¹H (500 MHz) and ¹³C-NMR (125 MHz) data of 1 (MeOD-d₄).

	δH in ppm (multiplicity, J in Hz)
H/C No.	Ha	Hb	δC in ppm (C-Type)*	H/C No.	δH in ppm (multiplicity, J in Hz)	δC in ppm (C-Type)*
1	2.03–1.97 (dt, 12.6, 3.5, 3.0)	1.03 (overlapped)	47.7 (CH2)	23	0.90 (s)	29.1 (CH3)
2	3.88 (dt, 10.0, 4.5, 3.0)	–	67.6 (CH)	24	0.98 (s)	18.2 (CH3)
3	4.64 (d, 10.0)	–	85.5 (CH)	25	1.08 (s)	17.2 (CH3)
4	–	–	40.2 (C)	26	1.03 (s)	26.6 (CH3)
5	1.06–1.04 (m)	–	56.8 (CH)	27	1.01 (s)	22.8 (CH3)
6	1.69–1.68 (m)	1.57 (br. s)	19.8 (CH2)	28	–	181.7 (C)
7	2.03–1.97 (dt, 12.6, 3.5, 3.0)	1.38 (br. s)	42.2 (CH2)	29	0.95 (s)	32.5 (CH3)
8	–	–	40.6 (C)	30	0.98 (s)	29.3 (CH3)
9	1.59 (br. s)	–	50.5 (CH)	1′	–	169.6 (C)
10	–	–	38.5 (C)	2′	7.59 (d, 16.0)	146.6 (CH)
11	1.73–1.71 (m)	1.69–1.68 (m)	18.6 (CH2)	3′	6.35 (d, 16.0)	115.8 (CH)
12	1.21–1.20 (m)	1.12 (m)	34.8 (CH2)	1″		127.9 (C)
13	–	–	40.2 (C)	2″	7.02 (d, 2.0)	115.1 (CH)
14	–	–	161.5 (C)	3″	–	146.8 (C)
15	5.60 (dd, 8.0, 3.5)	–	118.1 (CH)	4″	–	149.4 (C)
16	2.43–2.40 (m)	2.03–1.97 (dt, 12.6, 3.5, 3.0)	32.8 (CH2)	5″	6.81 (d, 8.5)	116.5 (CH)
17	–	–	52.1 (C)	6″	6.98 (dd, 8.5, 2.0)	122.9 (CH)
18	2.38–2.37 (m)	–	43.0 (CH)	OH	4.54 (br. s)
19	1.33–1.30 (m)	1.15–1.14	36.6 (CH2)	OH	1.41 (s)
20	–	–	30.2 (C)
21	1.69–1.68 (m)	1.51–1.45 (m)	33.1 (CH2)
22	1.83–1.79 (m)	1.65 (br. m)	34.0 (CH2)

a, b notations are δ_H (ppm) in a decreasing order. *C-type was deduced from DEPT experiments.

Table 2. ¹H-¹H COSY and ¹H-¹³C HMBC NMR data of 1.

Proton No.	^1H–^1H COSY	^1H–^13C HMBC	Proton No.	^1H–^1H COSY	^1H–^13C HMBC
H-1	H-2	C-2, C-3, C-4, C-24	H-22^d		–
H-2	H-1	C-3	H-23		C-3, C-4, C-5, C-24
H-3	H-2	C-2, C-4, C-23, C-24, C-1′	H-24		C-3, C-4, C-5, C-23
H-5	H-6	C-4, C-6, C-7	H-25		–
H-6*	H-7	C-7, C-8	H-26		C-8, C-9, C-13
H-7*	H-6	C-5, C-8	H-27		C-12, C-13
H-9		C-11, C-13, C-25	H-29		C-19, C-30
H-11*	–	C-13, C-14, C-25, C-27	H-30		C-19, C-20, C-29
H-12*	–	C-11	H-2′	H-3′	C-1′, C-3′, C-6″
H-15*	H-16	C-13	H-3′	H-2′	C-1′, C-1″
H-16*	H-15	C-13, C-14, C-15, C-17, C-28	H-2″	–	C-3″, C-4″, C-6″
H-18	H-19	C-13, C-14, C-15, C-17	H-5″	H-6″	C-1″, C-3″
H-19	H-18	C-20, C-21, C-22	H-6″	H-5″	C-4″, C-5″
H-21*	–	–

*Intra- and inter-crossed correlations in ¹H–¹H COSY.

Table 3. Cholinesterase inhibitory activities of compounds 1–5.

	% inhibition at 50 µg/mL		IC50 (µM)		Selectivity
Compounds	AChE	BChE	AChE	BChE	AChE*	BChE†
1	77.3 ± 2.34	85.6 ± 2.92	13.5 ± 0.95	10.6 ± 0.54	0.74	1.35
2	NA	98.3 ± 7.59	ND	17.8 ± 1.73	–	–
4	68.7 ± 3.16	NA	28.5 ± 0.78	ND	–	–
5	79.1 ± 1.94	90.5 ± 4.28	24.2 ± 0.99	19.1 ± 1.33	0.78	1.26
Physostigmine	ND	ND	0.04 ± 0.004	0.09 ± 0.003	2.25	0.44

Data presented as Mean ± SD (n = 3). *Selectivity for AChE is defined as IC₅₀(BChE)/IC₅₀(AChE).

†Selectivity for BChE is defined as IC₅₀(AChE)/IC₅₀(BChE).

NA, not active; ND, not determined.

Figure 2. Binding interaction of compound 1 with active site residues of TcAChE.

Table 4. Binding interaction data for compound 1 docked into active site gorge of AChE and BChE.

Entry	Ligand	Enzyme	Binding energy (kcal)	Interacting site	Residue	Type of interaction	Distance (Å)	Ligand interacting moiety
		TcAChE	−12.86	Pas*	Tyr 334	Hydrogen	3.11	COOH group
1	1			CT†	His 440	Hydrogen	2.23	C-3′
					Ser 200	Hydrogen	2.48	C-3′
		hBChE	−11.6	CT†	Ser 198	Hydrogen	2.40	COOH group

*Peripheral anionic site. †Catalytic triad.

Figure 3. Binding interaction of compound 1 with active site residue hBChE.

Table 5. Antioxidant activities of compounds 1–5.

Compounds	DPPH (IC50 in µM)	ABTS (IC50 in µM)	FRAP (μM TE)
1	7.76 ± 0.19	6.14 ± 0.28	183.2 ± 2.47
2–5	NA	NA	NA
Trolox	24.8 ± 0.62	12.6 ± 0.08	–
Gallic acid	7.92 ± 0.05	3.41 ± 0.03	–

Data presented as Mean ± SD (n = 3). NA, not active.