New Alkaloids from Margaritopsis carrascoana (Rubiaceae)

Abstract

Two new alkaloids containing N_b-methyl-triptamine units linked to bis-quinoline moieties, N-8”-formyl-calycosidine and N-8”-methyl-N-1’-demethyl-iso-calycosidine, were isolated from the aerial part of Margaritopsis carrascoana, along with known calycosidine and hodgkinsine. The cytotoxicity of the isolated alkaloids has been evaluated against cancer cell lines. The first two compounds showed only weak activity against HL-60 cell line, while hodgkinsine was the most active compound against HCT-116, OVCAR-8, HL-60 and SF-295 cancer cell lines. The structures of the isolated compounds were established by spectroscopic and molecular mechanical methods.

Keywords
Margaritopsis carrascoana; Rubiaceae alkaloids; N-8”-methyl-N-1’-demethyliso-calycosidine; N-8”-formyl-calycosidine; calycosidine; hodgkinsine

Introduction

The Rubiaceae family is known as a prolific source of alkaloids with great structural diversity and pharmacological properties. Among these, the pyrrolidinoindoline polymers, resulting from the condensation of several N_b-methyl-triptamine units, and those containing N_b-methyl-triptamine units linked to a bis-quinoline part, seem to be specific to the Psychotrieae tribe, particularly to the genera Calycodendron, Psychotria and Hodgkinsonia.^1-3

The genus Margaritopsis comprises about 50 species with pantropical occurrence, 27 of which are recognized in America and 15 are found in Brazil. It consists mainly of species that have been removed from the genus Psychotria L. (Rubiaceae) based on molecular data and geographic distribution.^4,5 The chemical studies of this genus is restricted to M. cymuligera, that revealed the presence of pyrrolidinoindoline alkaloids, largely found in species of Psychotria.⁶Margaritopsis carrascona is an endemic shrub from northeastern Brazil flora growing in the sandy soils of the region of Ibiapaba and Araripe plateaus in Ceará State. Previous chemical studies of its roots revealed glucosylated flavonoids with antioxidant activity.⁷ In this work, we report the isolation and structural characterization of two new alkaloids containing a N_b-methyl-triptamine unit linked to a bis-quinoline moiety, N-8”-formyl-calycosidine (1) and N-8”-methyl-N-1’-demethyl-iso-calycosidine (2), in addition to the known alkaloids calycosidine (3)¹ and hodgkinsine (4)² (Figure 1). The cytotoxicity of the isolated alkaloids have been evaluated against colorectal adenocarcinoma (HCT-116), ovarian carcinoma (OVCAR-8), human promyelocytic leukemia (HL-60) and glioma (SF-295) cancer cell lines.

Figure 1
Structures of alkaloids isolated from Margaritopsis carrascoana.

Experimental

General experimental procedures

Nuclear magnetic resonance (NMR) spectra were performed on a Bruker Avance DRX 500 spectrometer, equipped with an inverse detection probehead and z-gradient accessory working at 500.13 (¹H) and at 125.77 MHz (¹³C). All pulse sequences are standard in the Bruker XWIN-NMR software, and all experiments were conducted at room temperature. The samples, in 5 mm tube, were dissolved in CD₃OD (0.6 mL). Infrared (IR) spectra were recorded on a PerkinElmer FT-IR 1000 spectrometer (Waltham, USA). High resolution mass spectra were recorded on a QTOF mass spectrometer (Xevo-Waters, Milford, USA) by positive ionization mode of the electrospray ionization (ESI) source. Optical rotations were obtained on a PerkinElmer Q-2000 polarimeter (Waltham, USA) at 589 nm and 25 °C. High performance liquid chromatography (HPLC) analyses were performed on a Shimadzu chromatographer equipped with a ternary pump (Shimadzu LC-20AT) and UV detector (Shimadzu SPD-M20A, Kyoto, Japan), using Phenomenex RP-18 column (analytical: 250 × 4.6 mm, 5 µm; semi-preparative: 250 × 10 mm, 10 µm). HPLC grade solvents were purchased from Tedia Co. (São Paulo, Brazil) and the HPLC grade water was obtained by a Milli-Q purification system (Millipore, Bedford, USA). Thin layer chromatography (TLC) was performed on precoated silica gel aluminum sheets Merck (Kenilworth, USA) and the compounds were visualized by UV detection and spraying with Dragendorff reagent or vanillin/perchloric acid/EtOH solution, followed by heating.

Plant material

Aerial parts of Margaritopsis carrascoana (Delprete & E. B. Souza) C. M. Taylor & E. B. Souza were collected at the Moreilândia County, Araripe Plateau (Pernambuco State, Northeast of Brazil). A voucher specimen (No. 22075) has been deposited at the Herbário Prisco Bezerra (EAC) and identified by Prof Edson Paula Nunes, Departamento de Biologia, Universidade Federal do Ceará, Brazil.

Extraction and isolation

Dried aerial parts of M. carrascoana (7.6 kg) were exhaustively extracted with EtOH (3 × 9.0 L) at room temperature, followed by solvent evaporation under vacuum, yielding 295.5 g of extract. A portion of the extract (33.0 g) was treated with 10% aqueous HCl and the acid solution was extracted with EtOAc (3 × 150 mL). The aqueous phase was basified with NH₄OH to pH 9-10 and extracted with EtOAc (3 × 150 mL). The organic fractions were combined, and the solvent was evaporated to yield an alkaloid fraction (1.1 g), which was then chromatographed on a C18 cartridge [(H₂O/trifluoroacetic acid (TFA) 0.1%)/MeOH 1:1; (H₂O/TFA 0.1%)/MeOH 1:2; (H₂O/TFA 0.1%)/MeOH 1:3, and MeOH] yielding four fractions: F-1 (80 mL, 231.9 mg), F-2 (60 mL, 563.4 mg), F-3 (40 mL, 46.1 mg) and F-4 (100 mL, 84.8 mg). Fraction F-2 (563.4 mg) was submitted to semi-preparative RP-18 HPLC, using (H₂O/TFA 0.1%)/MeOH solutions with a gradient of 25% to 75% MeOH, to give five sub-fractions: F-2 (1) (15.1 mg, t_R = 5.5 min), F-2 (2) (95.6 mg, t_R = 6.2 min), F-2 (3) (90.0 mg, t_R = 8.9 min), F-2 (4) (59.2 mg, t_R= 12.1 min), and F-2 (5) (163.8 mg). Sub-fraction F-2 (1) (15.1 mg) was resubmitted to semi-preparative RP-18 HPLC, using (H₂O/TFA 0.1%)/MeOH 3:1 as eluent, to afford 1 (4.2 mg) and 2 (5.6 mg). Sub-fractions F-2 (2) (95.6 mg) and F-2 (4) (15.5 mg) were resubmitted to the former HPLC conditions to yield calycosidine 3 (50.6 mg) and hodgkinsine 4 (30.2 mg), respectively.

Molecular mechanics calculation

The lowest energy structures were obtained by a scanning method through the rotation of the dihedral angles of 60 degrees each. The corresponding structures were relaxed using the Gaussian 09 program from Gaussian INC, through de density functional theory (DFT) method B3LYP with the base-set 6-31+G (d,p). The continuous solvatation method polarizable continuum model (PCM) was applied to simulate the medium of the NMR experiment. Methanol was used as solvent. The semiempirical Austin model 1 (AM1) method yielded seven distinct and sterically allowed conformations for compound1, and two conformations for compound 2. The lowest energy conformations were relaxed with the DFT method.

Cytotoxic assays

Tumor cell lines colorectal adenocarcinoma (HCT-116), ovarian carcinoma (OVCAR-8), human promyelocytic leukemia (HL-60) and glioma (SF-295), provided by the National Cancer Institute (Bethesda, MD, USA), were used in this work. Cells were maintained in RPMI 1640 medium supplemented with 10% fetal bovine serum, 2 mmol L⁻¹ glutamine, 100 U mL⁻¹ penicillin, and 100 ug mL⁻¹ streptomycin at 37 °C with 5% CO₂. The cytotoxicity of all compounds was tested against tumor cell lines using the 3-(4,5-dimethyl-2-thiazolyl-2,5-diphenyl-2H-tetrazolium bromide) (MTT) (Sigma Aldrich Co., St. Louis, MO, USA) reduction assay.⁸ For all experiments, cells were plated in 96-well plates (10⁵cells per well for adherent cells or 3 × 10⁵cells per well for suspended cells in 100 µL of medium). The tested compounds (0.05-25 µg mL^-1) dissolved in dimethyl sulfoxide (DMSO) were added to each well, using the high-throughput screening-biomek (HTS) 3000-Beckman Coulter (Inc. Fullerton, California, USA), and incubated for 72 h. Doxorubicin was used as positive control. Control groups received the same amount of DMSO. After 69 h of incubation, the supernatant was replaced by fresh medium containing MTT (0.5 mg mL⁻¹). Three hours later, the MTT formazan product was dissolved in 150 µL of DMSO, and absorbance was measured at 595 nm (DTX 880 Multimode Detector, Beckman Coulter, Inc. Fullerton, CA, USA).

N-8”-Formyl-calycosidine (1)

Brown resin; [α]_D²⁵ = −4.6 (c 0.1, MeOH); IR (KBr) n_max / cm⁻¹ 3346, 2950, 2927, 2843, 1678, 1487, 1463, 1206, 1136, 841, 801, 756, 724; ¹H NMR (500 MHz, CD₃OD) and ¹³C NMR (125 MHz, CD₃OD), Table 1; HRESIMS (positive mode) m/z 547.3199 [M + H]⁺ (calcd. for C₃₄H₃₉N₆O, 547.3185).

Table 1
¹H NMR and ¹³C NMR (d in ppm and J in Hz) data and HMBC correlations of compounds 1 and 2

Position	1			Position	2
	δc	δH	HMBC		δC	δH	HMBC
2	47.9	3.12 (m) 2.74 (m)	8a, CH3-1	2	48.1	3.12 (m) 2.72 (m)	CH3-1
2’	47.8	2.60 (m) 2.18 (m)	CH3-1’	2’	38.7	3.04 (dd, J 13.9; 3.7) 2.54 (m)	3’
2”	46.3	3.05 (m) 2.98 (t, J 12.7)	CH3-1”	2”	46.9	2.89 (m) 2.82 (m)	CH3-1”, 3”
3	33.0	2.06 (m) 1.73 (br d, J 14.7)	-	3	33.5	2.13 (dt, J 14.3; 4.6) 1.82 (d, 13.1)
3’	33.1	2.18 (m) 1.62 (br d, J 12.2)	-	3’	32.4	2.21 (dt, J 13.9; 3.7) 1.59 (d, J 14.7)
3”	35.1	2.57 (m) 2.42 (m)	8”a	3”	36.2	2.57 (m) 2.47 (dt, J 14.3; 4.6)	8”a
3a	36.4	-	8a	3a	38.2	-	4, 8a
3’a	38.5	-	4’, 8’a	3’a	37.5	-	4’, 2’, 8’a, 3’
3”a	59.5	-	6’	3”a	60.7	-	6’, 4”, 8”a, 3”
4	127.8	7.37 (m)	6	4	127.5	7.67 (d, J 7.8)	6
4’	125.5	7.38 (m)	6’	4’	125.5	7.36 (m)	6’
4”	126.1	7.64 (m)	6”	4”	124.0	7.46 (d, J 7.5)	6”
4a	120.1	-	7, 5	4a	119.2	-	5, 7, 3
4’a	128.8	-	5’	4’a	131.2	-	H-5
4”a	135.5	-	7”, 5”, 8”a	4”a	133.9	-	5”, 7”, 8”a, 3’’
5	122.3	7.04 (m)	7	5	122.5	7.09 (m)	7
5’	124.1	7.15 (q, J 7.6)	4’	5’	123.7	7.06 (m)	-
5”	127.8	7.32 (m)	7”	5”	122.4	6.91 (t, J 7.8)	7”
6	130.7	7.29 (m)	4	6	131.4	7.36 (m)	4, 5
6’	124.8	7.68 (m)		6’	124.9	7.56 (d, J 7.4)	4’
6”	131.2	7.43 (m)	4”	6”	130.4	7.21 (t, J 7.8)	4”
7	115.5	6.95 (d, J 7.8)	5	7	115.9	6.99 (d, J 7.8)	5
7’	116.7		5’	7’	116.1	-	5’, 8”a
7”	113.2	7.56 (d, J 7.8)	5”	7”	113.4	6.83 (d, J 7.8)	5”
7a	143.2	-	6, 4, 8a	7a	143.7	-	4, 6, 8a
7’a	146.5	-	6’, 4’	7’a	145.5	-	6’, 4’, 8’a
7”a	140.2	-	CHO-8”, 6” 4”, 8”a, 7”	7”a	153.0	-	4”, 6”, 8”a CH3-8”
8a	73.9	5.48 (s)	CH3-1	8a	73.2	5.53 (s)	CH3-1
8’a	76.2	5.49 (s)	CH3-1’	8’a	67.9	6.25 (s)	2’
8”a	85.6	6.58 (s)	CHO-8”	8”a	95.1	5.78 (s)	CH3-8”, 3”
CHO-8”	163.3	9.18 (s)	-	CH3-1	40.8	2.84 (s)	-
CH3-1	40.5	2.81 (s)	-	CH3-1”	33.8	2.67 (s)	-
CH3-1’	41.3	2.41 (s)	-	CH3-8”	39.9	3.25 (s)	8”a
CH3-1”	33.7	2.66 (s)	-	-	-	-	-

N-8”-Methyl-N-1’-demethyl-iso-calycosidine (2)

Brown resin; [α]_D²⁵ = −3.3 (c 0.05, MeOH); IR (KBr) n_max / cm⁻¹ 3347, 2924, 2843, 1679, 1457, 1205, 1139, 845, 801, 724; ¹H NMR (500 MHz, CD₃OD) and ¹³C NMR (125 MHz, CD₃OD), see Table 1; HRESIMS (positive mode) m/z 519.3236 [M + H]⁺ (calcd. for C₃₃H₃₉N₆, 519.3246).

Results and Discussion

Compound 1 was isolated as a brown resin, [α]_D²⁵= −4.6º (c0.1, MeOH). The IR spectrum showed the presence of N−H (3346 and 2950 cm⁻¹), two absorptions related to aldehyde carbonyl (2843 and 1678 cm⁻¹) and benzene ring (1678, 1487 and 1463 cm⁻¹) functionalities. The molecular formula of compound 1 was established by the positive mode HRESIMS peak at m/z 547.3199 [M + H]⁺. Comparison of its mass spectrometry data with those obtained for the alkaloids hodgkinsine and calycosidine, isolated from other Psychotria species, suggested the same trimeric-type structure for compound1. The principal features were the presence of important ions at m/z 490.2646 and 433.2057, due to subsequent loss of C₃H₇N, typical fragments of the analogous calycosidine skeleton formed by one pyrrolidinoindoline and one calycanthine subunits attached at C-7’and C-3”a (Figure 2).⁹

Figure 2
HRESIMS diagnostic fragments observed for compounds 1 and 2.

The ¹H NMR spectrum of 1 corroborated the suggestion of the trimeric structure from the signals corresponding to six diastereotopic methylenes at δ_H 3.12 (m, H-2a), 2.74 (m, H-2b); δ_H 2.60 (m, H-2’a) and 2.18 (m, H-2’b); δ_H3.05 (m, H-2”a) and 2.98 (t, J 12.7 Hz, H-2”b), δ_H 2.06 (m, H-3a) and 1.73 (d, J 14.7 Hz, H-3b), δ_H 2.18 (m, H-3’a) and 1.62 (d, J12.2 Hz, H-3’b); δ_H 2.57 (m, H-3”a) and 2.42 (m, H-3”b), in addition to three N-methyl groups at δ_Η 2.81 (s, CH₃-1), 2.41 (s, CH₃-1’) and 2.66 (s, CH₃-1”), three methines at δ_H 5.48 (s, H-8a), 5.49 (s, H-8’a) and 6.58 (s, H-8”a), and one deshielded singlet at δ_H 9.17 (s, CHO-8”) relative to a formyl moiety. The presence of three subsystems formed by two ortho-disubstituted and one 1,2,3-trisubstituted aromatic rings was supported by the COSY correlations observed between the hydrogens at δ_H7.37 (H‑4) ↔ 7.04 (H‑5) ↔ 7.29 (H‑6) ↔ 6.95 (H‑7) (subsystem I); δ_H7.38 (H‑4’) ↔ 7.15 (H‑5’) ↔ 7.68 (H‑6’) (subsystem II) and δ_H7.64 (H‑4”) ↔ 7.32 (H‑5”) ↔ 7.43 (H‑6”) ↔ 7.56 (H‑7”) (subsystem III). In addition, the following vicinal and geminal correlations for three pairs of diastereotopic methylenes were observed: δ_H 3.12 (m, H-2a), 2.74 (m, H-2b) and δ_H 2.06 (m, H-3a), 1.73 (d, J14.7 Hz, H-3b); δ_H 2.60 (m, H-2’a), 2.18 (m, H-2’b) and δ_H 2.18 (m, H-3’a), 1.62 (d, J 12.2 Hz, H-3’b); and δ_H3.05 (m, H-2”a), 2.98 (t, J 12.7 Hz, H-2”b) and δ_H 2.57 (m, H-3”a), 2.42 (m, H-3”b). The unambiguous assignments of all carbons and hydrogens were possible by the HMQC spectrum analysis (Table 1). From these data it was possible to deduce the presence of the pyrrolidinoindole unit by the typical signal related to the methine carbon at δ_C 85.6 (C-8”a). The other methines at δ_C 76.2 and 73.9 accounted for carbons C-8’a and C-8a of the calycanthine unit.⁹ The HMBC spectrum showed long-range correlations in the pyrrolidinoindoline moiety between the methine proton at δ_H 6.58 (H-8”a) with the carbons at δ_C 135.5 (C-4”a), 140.2 (C-7”a) and 35.1 (C-3”), besides the correlations of the N-methyl group at N-1” (δ_H 2.66) with carbon at δ_C46.3 (C‑2”). The aromatic protons at δ_H 7.56 (H-7”) and 7.32 (H‑5”) showed correlations with the carbon at δ_C135.5 (C-4”a), whereas H-6” (δ_Η 7.43) and H-4” (δ_Η7.64) correlated with the carbon at δ_C 140.2 (C-7”a).

The position of the formyl group at N-8” was deduced on the basis of the correlations of the hydrogen at δ_H 9.18 (CHO) with carbons at δ_C 140.2 (7”a) and 85.6 (C-8”a) (Figure 3). The HMBC correlations for the calycanthine-type moiety were observed through the methine at δ_H 5.48 (H-8a) with carbons at δ_C 143.2 (C‑7a), 36.4 (C-3a) and 47.9 (C-2), whereas the aromatic protons at δ_H 7.04 (H‑5) and 6.95 (H-7) correlated with the carbon at δ_C 120.1 (C-4a), and the protons at δ_H 7.37 (H-4) and 7.29 (H-6) showed correlations with the carbon at δ_C 143.2 (C-7a). The other methine at δ_H 5.49 (H-8’a) showed correlations with carbons at δ_C 38.5 (C-3’a) and 146.5 (C-7’a), the aromatic proton at δ_H 7.15 (H-5’) correlated with carbons at δ_C 128.8 (C-4’a) and 116.7 (C-7’), whereas H-6’(δ_H7.68) and H-4’ (δ_H 7.38) showed correlations with the carbon at δ_C 146.5 (C-7’a). The N-1 methyl group at δ_H 2.81 showed correlation with the carbons at δ_C 47.9 (C-2) and 73.9 (C‑8a), while N-1’-Me (δ_H 2.41) correlated with the carbons at δ_C 47.8 (C-2’) and 76.2 (C-8’a).

Figure 3
HMBC correlations (H → C) of 1.

Molecular mechanics methods generated the most stable conformation for 1, that was consistent with the observed transanular nOe interactions in the NOESY spectrum (Figure 4). The key nOe cross-peaks observed between the pairs δ_H 1.62 (H-3’b) ↔ 5.48 (H-8a) ↔ 7.38 (H-4’); δ_H 2.06 (H-3a) ↔ 5.49 (H-8a’) ↔ 7.37 (H‑4); and δ_H 6.58 (H-8a”) ↔ 9.18 (CHO) ↔ 7.56 (H-7”) indicated that they were oriented in the same direction, and definitively determined the relative stereochemistry of 1, as a meso-calycanthine central subunit linked at C-7’ by one pirrolidineindole unit.

Figure 4
3D molecular models of 1 (1a-1c) and 2 (2a and 2b) depicting internal bond distances to explain key dipolar couplings observed through NOESY.

Compound 2 was isolated as a brown resin, [α]_D²⁵= −3.3º (c 0.05, MeOH). The IR spectrum showed bands relative to the presence of N−H (3346 and 2924 cm⁻¹) and aromatic ring (1678, 1457 and 1205 cm⁻¹) functionalities. The comparative analysis of its IR data with those observed for compound 1, revealed that formyl band was missing. The molecular formula of compound 2 was established by the positive mode HRESIMS peak at m/z [M + H]⁺ 519.3246, which undergo further fragmentations similar to those of 1, to form the ion peaks at m/z 462.2684 and 419.5402, relative to subsequent loss of C₃H₇N and C₂H₅N (Figure 2).

The support for a trimeric alkaloid calycosidine-type for compound 2 came from the comparative analysis of its NMR data with those observed for compounds 1 and 3, revealing them to be very similar. In the ¹H NMR spectrum of 2, the same signals related to the meso-calycanthine central subunit linked at C-7’ by one pirrolidineindole unit were observed (Table 1). However, the signal relative to the hydrogen of the formyl group at N-8’’ at d 9.18 observed for 1 was absent in 2, as well as the absence of carbonyl group at the ¹³C NMR spectrum. The long-range correlations in the HMBC spectrum between the typical methine of the pirrolidineindole moiety at δ_Η 5.78 (H-8”a) with the carbons at δ_C 46.9 (C-2”), 36.2 (C-3”) and 133.9 (C-4”a), and between both protons at δ_Η 2.67 (CH₃-1”) and 3.25 (CH₃-8”) with the methine carbon at δ_C 95.1 (C-8”a) determined the position of the N-methyl groups at N-1” and N-8”. Thus, compound 2 was determined as a structural analogue of calycosidine (3), where the N-group has migrated from N-1’ to N-8’’ (Figure 4). This suggestion was corroborated by the protonated molecule at m/z 519.3246 in the HRESIMS, that undergo further fragmentations to form the ion peaks at m/z 462.2684 and 419.5402, relative to subsequent loss of C₃H₇N and C₂H₅N (Figure 2).

The most stable conformation of 2 was generated by molecular mechanics methods, and supported the spatial interactions observed on the NOESY spectrum (Figure 5). The nOe cross peaks observed in the NOESY spectrum were in agreement with those proposed by the diagnostic correlations observed for the proton at δ_H 5.53 (H-8a) with those at δ_H 1.59 (H-3’b), 7.36 (H-4’) and 2.84 CH₃-1; the proton at δ_H 6.25 (H-8’a) with those at δ_H 1.82 (H-3b) and 7.67 (H-4), in addition to the correlations of the proton at δ_H 5.78 (H-8”a) with those at δ_H 2.57 (H-3”a), 3.25 (CH₃‑8”) and 2.67 (CH₃-1”).

Figure 5
HMBC correlations (H → C) of 2.

The alkaloids calycosidine (3) and hodgkinsine (4) are common in Psychotria species, and were isolated as the major constituents from the aerial parts of M. carrascoana. Calycosidine (3) was also obtained by transformation of hodgkinsine (4) under mild acidic conditions,⁹ and has been suggested as an artifact resulting from acid-base reaction during extraction the and isolation processes. Hodgkinsine is cited as anti-microbial, antinociceptive and as potent cytotoxic agent against HTC cell line.^10,11

The cytotoxicity of pyrrolidinoindoline alkaloids has been examined for potential applications as anti-cancer agents, and the statement of relationship between some structural patterns and the biological effects has been investigated.¹² Studies using hepatoma (HTC) cells in vitro revealed that the β-β’ bond in these compounds is important for the activity.¹³ The cytotoxic activity of 1-4 was assessed against human cancer cell lines HCT-116, OVCAR-8, HL-60 and SF-295. Based on data collected from three independent experiments, results showed that only hodgkinsine (4) exhibited effective action against HCT-116, SF-295 and OVCAR-8 cell lines with IC₅₀ values of 1.67, 1.0 and 1.41 µg mL⁻¹, respectively. Compound 2 exhibited a moderate effect against the HL-60 cell line with an IC₅₀ value of 14.19 µg mL⁻¹, whereas 1 and 3 showed IC₅₀ > 50 µg mL⁻¹. IC₅₀ values for doxorubicin were 0.12 (HCT-116), 0.02 (HL-60), 0.24 (SF-295) and 0.26 µg mL⁻¹ (OVCAR-8).

Conclusions

The isolation of alkaloids N-8’’-formyl-calycosidine (1) and N-8’’-methyl-N-1’-demethyl-iso-calycosidine (2) containing N_b-methyl-triptamine units from M. carrascoana reinforced the close relationship of the genera Margaritopsis and Psychotria, since both calycosidine (3) and hodgkinsine (4) have been found in P. rostrata. However, this is the first report of the isolation of structural analogues of calycosidine.

The cytotoxic activity of all compounds was evaluated against HCT-116, OVCAR-8, HL-60 and SF-295 cancer cell lines, where compounds 1 and 2 showed weak activity against HL-60, while hodgkinsine 4 was the most active compound against HCT-116, SF-295 and OVCAR-8. The current results suggest that, as already observed for Psychotria, the genus Margaritopsis is a prolific source of structurally interesting and biologically active alkaloids.

• Supplementary Information
  Supplementary data associated with this paper are available free of charge at http://jbcs.sbq.org.br as PDF file.

Acknowledgments

The authors are grateful to CNPq, CAPES, PADCT, PRONEX, FUNCAP and FINEP for the fellowships and financial support. We also thank to CENAUREMN and LEMANOR of Universidade Federal do Ceará, for NMR and high resolution mass spectra, respectively.

References

• ¹
  Libot, F.; Miet, C.; Kunesch, N.; Poisson, J.; Pusset, J.; Sévenet, T.; J. Nat. Prod 1987, 50, 468.
• ²
  Verrotta, L.; Pilati, T.; Tatò, M.; Elisabetsky, E.; Amador, T. A.; Nunes, D. S.; J. Nat. Prod. 1998, 61, 392.
• ³
  Parry, K. P.; Smith, G. F.; J. Chem. Soc., Perkin Trans. 1 1978, 1671.
• ⁴
  Andersson, L.; Syst. Geogr. Pl 2001, 71, 73.
• ⁵
  Taylor, C. M.; Syst. Geogr. Pl 2005, 75, 161.
• ⁶
  Brand, G.; Henriques, A. T.; Passos, C. S.; Baldoqui, D. C.; Santin, S. M. O.; Costa, W. F.; Saragiotto, M. H.; Biochem. Syst. Ecol 2012, 45, 155.
• ⁷
  Nascimento, R. R. G.; Monteiro, J. A.; Pimenta, A. T. A.; Trevisan, M. T. S.; Braz-Filho, R.; Souza, E. B.; Silveira, E. R.; Lima, M. A. S.; Quim. Nova 2014, 38, 60.
• ⁸
  Mosmann, T. J.; J. Immunol. Methods 1983, 65, 55.
• ⁹
  Libot, F.; Kunesch, N.; Poisson, J.; Kaiser, M.; Duddeck, H.; Heterocycles 1988, 27, 2381.
• ¹⁰
  Hassan-Elready, A. S.; El-Sharkawy, S. H.; Shier, W. T.; Planta Med 1995, 61, 313.
• ¹¹
  Amador, T. A.; Verotta, L.; Nunes, D. S.; Elisabetsky, E.; Planta Med 2000, 66, 770.
• ¹²
  Roth, A.; Kuballa, B.; Bounthanh, C.; Cabalion, P.; Sévenet, T.; Beck, J. P.; Anton, R.; Planta Med 1986, 52, 450.
• ¹³
  Adjibadé, Y.; Saad, H.; Kuballa, B.; Beck, J. P.; Sévenet, T.; Cabalion, P.; Anton, R.; J. Ethnopharmacol 1990, 29, 127.

Data availability

https://minio.scielo.br/documentstore/1678-4790/5F6qWTPnzKqNqKXbkpdLKkb/87d2c6c006bfec0675cb1df5a0befb1f546a2b95.pdf

Publication Dates

• Publication in this collection
  June 2015

History

• Received
  12 Dec 2014
• Accepted
  31 Mar 2015