Polyoxygenated seco-cyclohexenes derivatives from flower and leaf extracts of Desmos cochinchinensis and their α-glucosidase inhibitory activity.

Phytochemical investigations from the flower and leaf extracts of D. cochinchinensis resulted in the isolation and structural elucidation of five new polyoxygenated seco-cyclohexene derivatives, desmoscochinchinenes A-E (1-5), together with 11 known compounds (6-16). The structures on the new compounds were elucidated from their spectroscopic data, including UV, IR, NMR, and HRESITOFMS. Some of the isolated compounds were evaluated for their α-glucosidase inhibitory activities. Chrysin (9), pinocembrin 7-O-benzoate (12), and (-)-(5R)-desmoscochinoxepinone B (16) inhibited α-glucosidase better than the standard control (acarbose, IC50 = 83.5 μM) with IC50 values of 5.7, 33.8, 53.3 μM, respectively.

Introduction

Diabetes mellitus (DM) is a chronic metabolic disorder caused by an irregular rise in plasma glucose levels due to the unbalanced development of insulin or unresponsiveness to the influence of this hormone on cellular receptor signal transduction (Stojkovic et al., 2019). There are two underlying causes of diabetes mellitus: type 1 diabetes is a chronic condition that is characterized by the body's inability to produce insulin (Aathira and Jain, 2014), while its incapacity to regulate insulin response is called type 2 diabetes (Skyler et al., 2017). DM has also been reported the cause of many serious health problems, such as eyes (retinopathy), nerves (neuropathy), heart (stroke, coronary heart disease, and peripheral artery disease), teeth and gum problems, cancer, and depression (Emerging Risk Factors Collaboration, 2011). In diabetes treatment, regulation of the absorption rate of blood sugar from the small intestine by inhibiting digestive enzymes, such as α-glucosidase, is essential (Kim et al., 2008; Holman et al., 1999). Miglitol, acarbose, and voglibose are well-known commercial drugs used as an inhibitor of α-glucosidase in DM control, particularly type 2 diabetes (Saito et al., 1998; Xu et al., 2019). However, long-term use may result in undesirable side effects (Lee et al., 2014). Therefore, it is necessary to find new α-glucosidase inhibitors to treat diabetes in the future.

Desmos (Annonaceae) genus, a shrub or climbing plant, is wildly distributed in many Asian countries, including India, Myanmar, Thailand, Philippines, and Malaysia (Kuo et al., 2015) and five species, D. chinensis Lour, D. cochinchinensis Lour, D. crinitus Saff., D. dumosus (Roxb.) Saff., and D. macrocarpus Bân have been found in Thailand (Forest Herbarium-BKF, 2012). Desmos cochinchinensis Lour is a medium-sized shrub, which is used as a traditional medicine in South China for the treatment of malaria (Liao et al., 1989; Wu et al., 1994, 1997). There are two different flower forms (large petal and slim petal) of D. cochinchinensis (Figure 1) have been grown in Mae Fah University (Latitude: 20°04′48″N; Longitude: 99°89′43″E). Recently, we reported many new flavonoids and oxepinones from the leaf and twig extracts of D. cochinchinensis (large petal). Some of them showed interesting α-glucosidase inhibitory activity (Meesakul et al., 2019). In continuation of our studies on the different forms of the flower (slim petal) of the same plant, we report herein our studies of the flower and leaf extracts, which resulted in the isolation of 16 compounds (Figure 2), including five previously undescribed compounds. Furthermore, the α-glucosidase inhibitory activities of some of the isolated compounds are also reported.

Figure 1

Two different forms of flower of Desmos cochinchinensis growing in Mae Fah Luang University. (A) Slim petal of D. cochinchinensis. (B) large petal of D. cochinchinensis.

Figure 2

Compounds isolated from the flower and leaf extracts of D. cochinchinensis.

Materials and methods

General experimental procedures

The information on instruments and materials was the same as previous reports (Raksat et al., 2019; Phukhatmuen et al., 2020; Suthiphasilp et al., 2020). For more details, please see Supplementary Material.

Collection of plant materials

The flowers and leaves of D. cochinchinensis were collected in August 2015 from an authentically identified plant growing at Mae Fah Luang University Health Park, Chiang Rai Province, Thailand (GPS coordinates: 20°03′19″N 99°53′38″E). The plant was identified by Mr. Kithisak Aongyong and a voucher specimen (MFU-NPR0157) was deposited at the Natural Products Research Laboratory, School of Science, Mae Fah Luang University.

Extraction and isolation

The fresh flowers (1.72 kg) and air-dried leaves (567.4 mg) of D. cochinchinensis were individually extracted with MeOH (3 × 20 L) and EtOAc (3 × 10 L), respectively. The methanol extract (75.4 g) separated by quick column chromatography (QCC) over silica gel (hexanes- EtOAc, 1:0 to 0:1, v/v) to provide 11 fractions (F1–F11). F8 (32.7 mg) was further separated by CC eluting with ethyl acetate (EtOAc) in dichloromethane (CH2Cl2) (0.5:10, v/v) to give four fractions (F8A-F8D). Separation of F8C (10.5 mg) by reverse phase (RP) C18 high-performance liquid chromatography (HPLC) eluting with an isocratic system of acetonitrile (CH3CN) in water (H2O) (0.9:1.1, v/v, 2.0 mL/min) gave compounds 3 (3.1 mg, tR 30.8 min) and 11 (4.1 mg, tR 55.6 min). F11 (735.1 mg) was separated by Sephadex-LH20 eluting with MeOH to provide four fractions (F11A-F11D). Purification of F11C (274.1 mg) by RP C18 HPLC eluting with an isocratic system of MeOH in H2O (0.7:1.3, v/v, 2.0 mL/min) provided seven fractions (F11CA-F11CG). Further separation of F11CC (10.5 mg) by RP C18 HPLC eluting with an isocratic system of MeOH in H2O (0.7:1.3, v/v, 2.0 mL/min) gave compound 4 (2.3 mg, tR 21.2 min). Compound 5 (7.1 mg, t 11.7 min) was obtained from F11CG (21.7 mg) by RP C18 HPLC eluting with an isocratic system of MeOH in H2O (0.5:1.5, v/v, 2.0 mL/min). For the details of isolation procedures for known compounds, see Supplementary Material.

Similarly, the EtOAc extract (36.7 g) was separated by QCC over silica gel (hexanes in EtOAc, 1:0 to 0:1, v/v) to provide eight fractions (L1-L8). L4 (4.08 g) was further separated by CC eluting with EtOAc in hexanes (1:5, v/v) to give eight fractions (L4A-L4H). Fraction L4F (17.7 mg) by RP C18 HPLC eluting with an isocratic system of CH3CN in H2O (0.7:1.3, v/v, 2.0 mL/min). Fraction L4FB (3.8 mg) was further purified by PTLC eluting with EtOAc in hexanes (1:0.3, v/v) yielded compound 2 (1.1 mg). Fraction L4H (30.2 mg) was isolated by CC eluting with EtOAc in CH2Cl2 (0.5:10, v/v) gave compounds 1 (4.1 mg) and 4 (2.1 mg). For the details of isolation procedures for known compounds, see Supplementary Material.

Desmoscochinchinene A (): Colorless viscous oil; UV (MeOH) λ (log ε) 232 (3.47) and 272 (2.81) nm, IR (neat) ν 2944.6, 1723.8, 1374.7, 1270.9, 1112.9, and 712.9 cm−1; 1H and 13C NMR, see Tables 1 and 2; HRESITOFMS m/z 311.0901 [M + Na]+ (calcd without Na ion for C16H16O5, 288.1009).

Table 1

1H NMR spectroscopic data (mult., J in Hz, 600 MHz) of compounds 1-5.

position	1a	2a	3b	4a	5a
1	5.00, s	5.21, s	4.28, s	4.47, s	4.76, s
3	6.60, d (11.5)	7.48, m	6.50, d (11.8)	6.51, d (11.5)	6.57, d (11.3)
4	7.52, dd (15.2, 11.5)	6.95, t (11.0)	6.46, t (11.8)	6.47, t (11.5)	6.49, t (11.3)
5	6.26, dd (15.2, 7.8)	6.21, dt (11.0, 6.8)	5.67, dt (11.8, 6.5)	5.71, dt (11.5, 7.0)	5.74, dt (11.3, 7.0)
6	9.68, d (7.8)	4.97, d (6.8)	4.32, d (6.5)	4.82, d (7.0)	4.77, d (7.0)
7	4.97, s	9.68, s	4.21, s	4.36, s	4.66, s
OBz
3′, 7′	8.07, d (7.4)	8.08, d (7.8)
4′, 6′	7.47, t (7.4)	7.48, m
5′	7.60, t (7.4)	7.61, t (7.8)
1-OCOCH3					2.09, s
6-OCOCH3		2.16, s		2.12, s	2.07, s
7-OCOCH3	2.08, s				2.06, s

recorded in CDCl3.

recorded in CD3OD.

Table 2

13C NMR spectroscopic data (150 MHz) of compounds 1-5.

position	1a	2a	3b	4a	5a
1	65.3	55.1	56.3	59.1	58.9
2	139.9	136.5	140.7	140.9	132.0
3	128.8	144.4	120.3	126.1	126.4
4	144.0	125.4	122.4	121.8	125.5
5	134.2	135.9	130.6	126.2	128.0
6	193.1	59.4	56.7	59.7	59.6
7	59.0	192.5	63.2	66.4	65.8
OBz
1′	165.5	166.2
2′	129.4	137.7
3′, 7′	129.3	129.3
4′, 6′	128.2	128.0
5′	133.1	132.8
1-OCOCH3					170.4
1-OCOCH3					20.4
6-OCOCH3		170.7		170.7	170.4
6-OCOCH3		20.4		20.1	20.5
7-OCOCH3	170.2				170.2
7-OCOCH3	20.3				20.5

recorded in CDCl3.

recorded in CD3OD.

Desmoscochinchinene B (): Colorless viscous oil; UV (MeOH) λ (log ε) 233 (3.39) and 268 (2.76) nm, IR (neat) ν 2944.7, 1725.8, 1452.3, 1271.9, 1112.9, 1027.3, and 713.0 cm−1; 1H and 13C NMR, see Tables 1 and 2; HRESITOFMS m/z 311.0895 [M + Na]+ (calcd without Na ion for C16H16O5, 288.1005).

Desmoscochinchinene C (): Colorless viscous oil; UV (MeOH) λ (log ε) 232 (3.62) and 277 (2.69) nm, IR (neat) ν 3293.1, 2873.7, 1651.0, 1413.9, and 1001.6 cm−1; 1H and 13C NMR, see Tables 1 and 2; HRESITOFMS m/z 167.0690 [M + Na]+ (calcd without Na ion for C7H12O3, 144.0797).

Desmoscochinchinene D (): Colorless viscous oil; UV (MeOH) λ (log ε) 238 (3.30) nm, IR (neat) ν 3429.1, 2926.8, 1720.8, 1629.9, 1270.9, 1098.5, and 713.9 cm−1; 1H and 13C NMR, see Tables 1 and 2; HRESITOFMS m/z 209.0792 [M + Na]+ (calcd without Na ion for C9H14O4, 186.0899).

Desmoscochinchinene E (): Colorless viscous oil; UV (MeOH) λ (log ε) 240 (3.31) nm, IR (neat) ν 2926.8, 1739.4, 1376.8, 1227.5, 1026.2, and 966.1 cm−1; 1H and 13C NMR, see Tables 1 and 2; HRESITOFMS m/z 293.0999 [M + Na]+ (calcd without Na ion for C13H18O6, 270.1107).

(−)-(2S)-Pinocembrin 7-O-benzoate (): Yellow amorphous solid; − 117 (c 0.1, CHCl3), UV (MeOH) λ (log ε) 328 (1.92), 290 (2.32), and 216 (2.54) nm, IR (neat) ν 2927, 1744, 1650, 1633, 1244, 1128, and 704 cm−1; ECD (5.41 × 10−3 M, MeOH) λ (Δε) 222 (+3.96), 284 (-3.99) and 321 (+3.34) nm. 1H and 13C NMR, see Table 3; HRESITOFMS m/z 361.1078 [M + H]+ (calcd without H ion for C22H16O5, 360.1004).

Table 3

1H (600 MHz) and 13C (150 MHz) NMR spectroscopic data of compounds 12 in CDCl3.

Position	12
	δH (mult., J in Hz)	δC
2	5.50, dd (13.2, 3.0)	79.3
3	3.16, dd (17.2, 13.2);2.91, dd (17.2, 3.0)	43.6
4		196.9
4a		106.3
5		163.4
6	6.46, brs	103.5
7		162.3
8	6.46, brs	101.9
8a		158.7
1′		138.0
2′, 3′, 5′, 6′	7.42–7.48, m	128.9
4′	7.41, m	128.6
1″		164.0
2″		128.8
3″, 7″	8.17, d (7.5)	130.3
4″, 6″	7.52, t (7.5)	126.1
5″	7.66, t (7.5)	133.9
5-OH	11.90, s

Biological assay

α-Glucosidase inhibitory assay

A colorimetric α-glucosidase assay was conducted according to the previously described method (Sharma et al., 2019; Phukhatmuen et al., 2020; Suthiphasilp et al., 2020), using acarbose as a positive control (IC50 = 83.5 μM).

NO production inhibitory and cytotoxicity assays

The nitric oxide production assay (Joo et al., 2014; Suthiphasilp et al., 2020) and cytotoxicity assay (Ahmed et al., 1994) were performed according to the method described in the literature with slight modification. Indomethacin (IC50 value at 32.2 μM) was used as a positive control.

Glucose uptake assay

The glucose uptake assay was performed according to the method described in the previous reports (Sharma et al., 2019; Phukhatmuen et al., 2020; Cheng et al. (2006)) with modification. Metformin (1 mM) and insulin (1 μM) were used as positive controls in the glucose uptake assay with 1.9- and 2.07-fold induction, respectively. For more details, please see Supplementary Material.

Results

Structure of the isolated compounds from the flower (slim petal) and leaf extracts of D. cochinchinensis

The flower (slim petal) and leaf extracts of D. cochinchinensis were individually separated and purified by various chromatography techniques, which led to the isolation and identification of five new polyoxygenated seco-cyclohexenes (1–5), together with 11 known compounds (6–16). Two new compounds 1 and 2 were obtained from the leaf extract, while three new compounds 3–5 were obtained from the flower extract. The known compounds were characterized by the comparison of their physical properties and spectroscopic data with the previous reports and identified as flexuvarin B (6) (Hsu et al., 2016), flexuvarin C (7) (Hsu et al., 2016), flexuvarin D (8) (Hsu et al., 2016), chrysin (9) (Meesakul et al., 2017), 5-hydroxy-7-methoxyflavone (tectochrysin) (10) (Righi et al., 2010), pinocembrin (11) (Meesakul et al., 2017), pinocembrin 7-O-benzoate (12) (Hoeneisen et al., 1993), 2′-hydroxy-4′,6′-dibenzyloxychalcone (13) (Drewes and van Vuuren, 2008), zeylenone (14) (Suthiphasilp et al., 2019), 1R,6S-cherrevenol A (15) (Auranwiwat et al., 2019), and (−)-(5R)-desmoscochinoxepinone B (16) (Meesakul et al., 2019) (Figure 2).

α-Glucosidase inhibitory, NO production inhibitory, and glucose uptake activities of the isolated compounds from the flower (slim petal) and leaf extracts of D. cochinchinensis

Only the stable compounds of adequate amounts (3, 6, 7, 9, 11–13, and 16) were evaluated for their α-glucosidase inhibitory, nitric oxide (NO) production inhibitory, and glucose uptake activities. Of these, compounds 9, 12, and 16 exhibited α-glucosidase inhibitory activity better than standard control, acarbose (IC50 = 83.5 μM) with the half-maximal inhibitory concentration (IC50) values of 5.7, 33.8 and 53.3 μM (Table 4). In contrast, the remaining compounds were found to be inactive. It should be noted that the flavonoids 9 and 12 and the oxepinone 16 strongly inhibited α-glucosidase. While, the seco-cyclohexenes 3, 6, and 7 showed weak α-glucosidase inhibition with IC50 values of more than 100 μM. None of these compounds had NO production inhibitory or glucose uptake activities.

Table 4

α-Glucosidase inhibitory activity of some isolated compounds from flowers and leaves of D. cochinchinensis.

Compound	α-glucosidase inhibitory activity (IC50 (μM)
3	inactive
6	inactive
7	inactive
9	5.7
10	inactive
11	inactive
12	33.8
13	inactive
16	53.3
Acarbose	83.5

Discussion

The 1H nuclear magnetic resonance (NMR) spectra of the new compounds 1–5 displayed the common characteristic resonances of a polyoxygenated seco-cyclohexene skeleton; including those for three olefinic protons at ca. δH 6.5–7.4 (H-3), δH 6.4–7.5 (H-4), and δH 5.6–6.2 (H-5) and one oxymethylene group at ca. δH 4.2–5.2 (H-1).

Desmoscochinchinene A (1) gave a molecular formula of C16H16O5, as indicated by its NMR and high-resolution electrospray ionization time-of-flight mass spectrometry (HRESITOFMS) data ([M + Na]+ m/z 311.0901). The 1H and 13C NMR spectroscopic data of 1 (Tables 1 and 2) displayed resonances typical of an of polyoxygenated seco-cyclohexene (one benzoyl unit [(δH 8.07 (2H, d, J = 7.4 Hz, H-3′ and H-7′), 7.47 (2H, t, J = 7.4 Hz, H-4′ and H-6′) 7.60, (1H, t, J = 7.4 Hz, H-5′)], three olefinic protons [δH 6.60 (1H, d, J = 11.5 Hz, H-3), 7.52 (1H, dd, J = 15.2, 11.5 Hz, H-4), 6.26 (1H, dd, J = 15.2, 7.8, H-5], two oxymethylene groups [δH 5.00 (2H, s, H-1) and 4.97 (2H, s, H-1)], and one acetoxy group [δH 2.08 (3H, s, 7-OCOCH)]), which were similar to those of flexuvarin B (6) previously isolated from Uvaria flexuosa (Hsu et al., 2016). The major difference was found that a 6-O-acetyl group of flexuvarin B (6) was replaced by an aldehyde group, which displayed the formyl proton resonance at δH 9.68, (1H, d, J = 7.8 Hz, H-6). The configuration of the Δ3,4 and Δ4,5 alkene units were assigned as Z (Δ3,4) and E (Δ4,5) based on the magnitude of their coupling constants (J) of 11.5 and 15.2 Hz, respectively. The heteronuclear multiple bond connectivity (HMBC) correlations of H-6 (formyl proton) to C-5 (δC 134.2) and H-4 and H-5 to C-6 (δC 193.1) confirmed this assignment. Other HMBC correlations supporting the characterization of compound 1 was shown in Figure 3.

Figure 3

Selected HMBC correlations of isolated compounds 1–5 and 12.

Desmoscochinchinene B (2) gave the same molecular formula, C16H16O5, as desmoscochinchinene A, which showed an ion peak at m/z 311.0895 [M + Na]+ in the HRESITOFMS data. The NMR spectroscopic data (Tables 1 and 2) of compound 2 were almost identical to those of desmoscochinchinene A. The main difference is only the location of the O-acetyl and formyl groups. Compound 2 contained the formyl group at C-7 and O-acetyl group at C-6, whereas in compound 1, these groups were at C-6 and C-7, respectively. These assignments were confirmed by the HMBC correlations between the formyl proton (δH 9.68) with C-1 (δC 55.1) and H-1 (δH 5.21) and H-3 (δH 7.48) with C-7 (δC 192.5), and H-6 (δH 4.97) and the methyl proton of acetoxy group (δH 2.16) with carbonyl carbon of acetoxy group (δC 170.7). The configuration of the Δ3,4 and Δ4,5 alkene units were assigned as Z based on the magnitude of the coupling constant (J) of 11.0 Hz. The key HMBC correlations were supported by the structural characterization of compound 2, displayed in Figure 3.

Desmoscochinchinenes C (3), D (4), and E (5) were isolated as colorless viscous oils. Their NMR spectroscopic data (Tables 1 and 2) were similar to those of desmoscochinchinene B (2) except for the lack of resonances for the benzoyl and formyl groups at C-1 and C-7, respectively. The molecular formula, C7H12O3, of compound 3 was deduced from HRESITOFMS, which showed an ion peak at m/z 167.0690 [M + Na]+. The structure of 3 is a simple polyoxygenated seco-cyclohexene containing the same substituent group, hydroxymethyl unit, on C-1 (δH 4.28/δC 56.3), C-6 (δH 4.32/δC 56.7), and C-7 (δH 4.21/δC 63.2). These assignments were supported by the HMBC correlations, as shown in Figure 2. The molecular formula of desmoscochinchinene D (4) (C9H14O4, HRESITOFMS m/z 209.0792 [M + Na]+) indicated compound 4 contained an acetyl unit when compared to that of compound 3. The NMR spectroscopic data of 4 (Tables 1 and 2) displayed an additional acetyl group at δH 2.12/δC 20.1 and δC 170.7. The HMBC correlations between methyl proton of an acetyl group (δH 2.12) and H-6 (δH 4.82) with the carbonyl carbon of the acetyl unit (δC 170.7) confirmed this assignment. The structure of 5, HRESITOFMS m/z 293.0999 [M + Na]+, corresponding to the molecular formula of C13H18O6, was closely related to that of 3. The main differences were found that all hydroxymethyl units in 3 were replaced by acetoxy units [1-OCOCH3 (δH 2.09/δC 20.4 and δC 170.4), 6-OCOCH3 (δH 2.07/δC 20.5 and δC 170.4), and 7-OCOCH3 (δH 2.06/δC 20.5 and δC 170.2)] and H-1 (δH 4.76, s), H-6 (δH 4.77, d, J = 7.0 Hz), and H-7 (δH 4.66, s) shifted to the lower field in 5. The configuration of the Δ3,4 and Δ4,5 alkene units for 3, 4, and 5 were identified according to their J coupling constants, which were similar to those of compound 2. All these assignments were supported by HMBC correlations, as shown in Figure 3.

The biosynthetic pathway of polyoxygenated cyclohexene and seco-cyclohexene were proposed from the shikimic acid pathway (Hsu et al., 2016; Macabeo et al., 2017; Suthiphasilp et al., 2019). The primary intermediate A as shown in Figure 4, is proposed as a forerunner based on our results. The enzymatic cleavage at C-6/C-7 would yield compound 3. Selective acetylation at 6-OH of compound 3 or fully acetylation could produce compounds 4 and 5, respectively. Benzoylation of 3 at 1-OH would produce intermediate B, which was further acetylation at 6-OH and followed by oxidation at 7-OH would provide compounds 8 and 2, respectively. On the other hand, acetylation at 7-OH and followed by oxidation at 6-OH would obtain compound 7, and followed by isomerization at Δ4,5 alkene unit could give compound 1, respectively. Multi-steps of oxidation and acylation of intermediate A would reach to compounds 14 and 15, whereas compound 16 would obtain from compound 3 via oxidation, cyclization, and acetylation.

Figure 4

Putative biosynthesis pathway for seco-cyclohexenes derivatives compounds 1–8 and 14–16.

Compound 12, pinocembrin 7-O-benzoate, was first isolated from Pachylaena atriplicifolia in 1993 by Hoeneisen and co-worker (Hoeneisen et al., 1993), but its 13C and full 2D NMR data, specific rotation, and absolute configuration were not provided. The HRESITOFMS of pinocembrin 7-O-benzoate displayed an ion peak at m/z 361.1078 [M + H]+ corresponding to the molecular formula C22H16O5. The 1H and 13C NMR spectroscopic data (Table 3) showed the characteristic resonances for a flavanone skeleton (Hoeneisen et al., 1993); δH/δC 5.50 (1H, dd, J = 13.2, 3.0 Hz, H-2)/79.3, 3.16 (1H, dd, J = 17.2, 13.2, H-3a) and 2.91 (1H, dd, J = 17.2, 3.0, H-3b)/43.6), 6.46 (1H, brs, H-6)/103.5, 6.46 (1H, brs, H-8)/101.9, 7.46 (4H, m, H-2′, H-3′, H-5′, and H-6′)/128.9 (× 4), 7.41 (1H, m, H-4′)/128.6, and δC 138.0 (C-1′). The hydrogen bonded-hydroxy proton at δH 11.90 was placed at C-5 due to the HMBC correlations between this proton resonance with those of C-4a (δC 106.3), C-5 (δC 163.4), and C-6 (δC 103.5). Finally, the benzoyloxy group [δH/δC 8.17 (2H, d, J = 7.5 Hz, H-3″ and H-7″)/130.3), H-4′′/H-6″ 7.52 (2H, d, J = 7.5 Hz, H-4″ and H-6″)/126.1), 7.66 (1H, d, J = 7.5 Hz, H-5″)/133.9), δC 164.0 (C-1″), and δC 128.8 (C-2″)] was placed at C-7 by of the process of elimination. Full assignments of 1H and 13C NMR spectroscopic data are summarized in Table 3. The (2S) absolute configuration of compound 12 was identified by the comparison of its electronic circular dichroism (ECD) spectrum [222 (+3.96), 284 (−3.99), and 321 (+3.34) nm] to that of well know compound 11 [214 (+3.70), 283 (−3.57), and 319 (+2.98)], which were very similar to each other (Figure 5). Therefore, compound 12 was identified as (−)-(2S)-pinocembrin 7-O-benzoate (−117, c 0.1, CHCl3).

Figure 5

ECD spectra of compounds 11 and 12 (MeOH).

Conclusion

Phytochemical investigations of the flower and leaf extracts of the D. cochinchinensis resulted in the identification and elucidation of 16 compounds, five of these compounds were new polyoxygenated seco-cyclohexenes 1–5. The previous investigations have been reported that flavonoids are major compounds in Desmos species. To the best of our knowledge, polyoxygenated seco-cyclohexenes 1–8 were found in the genus of Desmos for the first time. Chrysin (9) showed good α-glucosidase activity with the IC50 values of 5.7 μM, which could have potential as a lead compound for antidiabetic agent development.

Declarations

Author contribution statement

Surat Laphookhieo: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper.

Tharakorn Maneerat: Conceived and designed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Virayu Suthiphasilp: Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Raymond J. Andersen, Stephen G. Pyne, Rawiwan Charoensup, Thidarat Duangyod: Analyzed and interpreted the data; Wrote the paper.

Funding statement

Surat Laphookhieo was supported by (DBG6280007 & DBG6180029). Surat Laphookhieo & Virayu Suthiphasilp was supported by (PHD/0133/2559). Virayu Suthiphasilp was supported by .

Data availability statement

Data included in article/supplementary material/referenced in article.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.