α-Amylase and dipeptidyl peptidase-4 (DPP-4) inhibitory effects of Melicope latifolia bark extracts and identification of bioactive constituents using in vitro and in silico approaches

Figures & data

Table 1. Extraction yield of various M. latifolia extracts.

Plant part	Extracts	Extraction yield (%)
Stem bark	Hexane	0.54 ± 0.11^a
	Chloroform	1.80 ± 0.03^b
	Methanol	2.10 ± 0.19^c

All values were expressed as mean ± standard deviation of triplicates. Data with different superscript (a, b, c) were considered significant (p < 0.05).

Figure 1. Chemical structures of β-sitosterol (1), halfordin (2), methyl p-coumarate (3), and protocatechuic acid (4).

Table 2. α-Amylase and DPP-4 inhibitory activities of various M. latifolia extracts.

Extracts	IC50 (μg/mL)
	α-Amylase	DPP-4
Hexane	8113.15 ± 103.15^c	5872.03 ± 211.67^c
Chloroform	1464.32 ± 312.19^a	221.58 ± 32.01^a
Methanol	2941.17 ± 113.72^b	990.21 ± 25.59^b

All values were expressed as mean ± standard deviation of triplicates. Data with different superscript (a, b, c) in the same column were considered significant (p < 0.05).

Table 3. α-Amylase and DPP-4 inhibitory activities of M. latifolia fractions and isolated compounds.

	IC50 (μg/mL)
	α-Amylase	DPP-4
Fractions
CF1	954.63 ± 32.09^h	581.50 ± 12.77^d
CF2	1025.41 ± 218.64^i	80.40 ± 6.84^b
CF3	397.68 ± 10.41^f	37.16 ± 3.02^a
CF4	831.72 ± 9.25^g	160.00 ± 15.21^c
Compounds
1	154.4 ± 15.80 (372.31 ± 2.62 μM)^c	ND
2	54.53 ± 3.19 (197.53 ± 4.18 μM)^a	ND
3	220.60 ± 9.11 (1238.90 ± 22.05 μM)^e	162.40 ± 1.45 (911.44 ± 7.61 μM)^c
4	89.31 ± 11.30 (579.94 ± 3.18 μM)^b	ND
Sitagliptin	–	0.014 ± 0.01 (0.034 ± 0.04 μM)^f
Acarbose	182.31 ± 20.16 (282.39 ± 8.14 μM)^d	–

ND: not determined where IC₅₀ was not detected at highest tested concentration (1 mg/mL). ‘–’: Not available. All values were expressed as mean ± standard deviation of triplicates. Data with different superscript (a, b, c, d, e, f, g, h, i) in the same column were considered significant (p < 0.05).

Figure 2. Two-dimensional (2D) interaction diagram of the identified compounds with amino acid residues of α-amylase: (a) acarbose; (b) halfordin, 2; (c) β-sitosterol, 1; (d) protocatechuic acid, 4; (e) methyl p-coumarate, 3.

Figure 3. Two-dimensional (2D) interaction diagram of the identified compounds with amino acid residues of DPP-4: (a) sitagliptin and (b) methyl p-coumarate, 3.

Table 4. DPPH-free radical scavenging activity and β-carotene bleaching activity of M. latifolia fractions and isolated compounds.

	DPPH	β-Carotene bleaching activity
	IC50 (μg/mL)	AA (%)
Fractions
CF1	207.91 ± 0.02^e	62.87 ± 0.04^d
CF2	601.87 ± 0.04^g	59.89 ± 0.03^e
CF3	399.03 ± 0.05^f	58.90 ± 0.06^e
CF4	182.88 ± 0.03^d	46.43 ± 0.02^f
Compounds
1	ND	49.46 ± 0.03^f
2	1776.01 ± 0.16 (6429.23 ± 0.16 μM)^h	88.48 ± 0.02^b
3	ND	1.08 ± 0.02^g
4	–	–
Ascorbic acid	15.00 ± 0.01 (85.17 ± 0.01 μM)^b	35.23 ± 0.02^g
α-Tocopherol	18.79 ± 0.01 (43.63 ± 0.01 μM)^c	98.01 ± 0.02^a
BHT	9.90 ± 0.03 (44.93 ± 0.03 μM)^a	76.42 ± 0.02^c

ND: Not determined where IC₅₀ was not detected at highest tested concentration (1 mg/mL). ‘-’: Not available. All values were expressed as mean ± standard deviation of triplicates. Data with different superscript (a, b, c, d, e, f, g, h) in the same column were considered significant (p < 0.05).