The genus Artocarpus (Moraceae) comprises about 50 species, distributed mainly in Southeast Asia. Most of them are used as traditional folk medicine and have great potential medicinal values. Artocarpus tonkinensis A. Chev. ex Gagnep., occurs in North Vietnam and China [1, 2]. The decoction of its leaves has for a long time been used in Vietnamese traditional medicine for the treatment of backache and joint disorders [1, 3]. From the bark of Artocarpus tonkinensis the novel benzofuran artotokin, several flavonoids, triterpens, and stilbene, while from its roots isoprenyl flavonoids (artotonins A and B), along with 13 other known compounds, have been isolated and identified [2, 4]. Our previous phytochemical investigations have shown the presence of maesopsin 4-O-β-D-glucopyranoside (1), alphitonin-O-β-D-glucoside (2) and artonkin-4′-O-β-Dglucopyranoside (3) as well as kaempferol 3-O-β-D-glucopyranoside (5) in its leaves [1, 5]. The polar extracts (BuOH, EtOH) and the main isolated compound 1 have shown potent antiproliferative and anti-inflammatory effects both in vitro and in vivo [1, 3, 5]. Besides the already reported four compounds (1–3, 5) [1, 2], four other compounds 4 and 6–8 were also obtained from the n-butanol extract.

The structure of 4 was identified as 3,4′,5,7-tetrahydroxyflavone ( kaempferol) on the basis of MS, NMR spectroscopic data, and comparison with reported data [6].

figure a

Compound 6 was isolated together with compound 7 as a brown-yellow powder mixture. The HR-ESI-MS showed a pseudo-molecular peak at m/z 617.1476 [M + Na]+ (calcd for C27H30O15Na, 617.1477) in the positive ion mode, while in the negative ion mode it exhibited a molecular peak at m/z 593.1484 [M – H]– (calcd for C27H29O15, 593.1506). Additionally, this spectrum also showed fragment ion peaks at m/z 487.0847 [M + Na – Rha]+ (calcd for C21H20O12Na, 487.0852) and at m/z 463.0863 [M – H – Rha]– (calcd for C21H19O12, 463.0877). Furthermore, the EI-MS spectrum showed only a major ion peak at m/z 286, characteristic of aglycon as kaempferol (4). The above mass spectral data suggested that the two compounds have the same molecular formula as C27H30O15 and is mixture of kaempferol 3-rutinoside (6) and kaempferol 3-neohesperidoside (7) [7]. The HSQC, HMBC, and 13C NMR spectral data enabled the complete identification of the structures which were assigned as kaempferol 3-rutinoside (6) and kaempferol 3-neohesperidoside (7) [7].

Compound 8 was obtained as an amorphous yellow semisolid. The positive HR-ESI-MS gave molecular ion peaks at m/z 747.1885 [M + Na]+ (calcd for C36H36O16Na, 747.1901) and 725.2077 [M + H]+ (calcd for C36H37O16, 725.2082), corresponding to the molecular formula C36H36O16. Compound 8 was deduced as a flavonoid dimer with one hexose unit. This was supported by a fragment ion peak at m/z 563.1527 [M + H – 162]+ (calcd for C30H27O11, 563.1553), indicating its aglycone (C30H26O11). Furthermore, its HR-ESI-MS also showed fragment peaks at m/z 273.0746 (calcd for C15H13O5, 273.0763) and 291.0853 (calcd for C15H15O6, 291.0869) corresponding to afzelechin and catechin units, respectively. A fragment ion peak at m/z 435.1268 (calcd for C21H23O10, 435.1291) confirmed the linkage of the hexose to the afzelechin unit. Consistent with the mass spectrum, the PMR spectrum displayed signals belonging to two flavan-3-ol skeletons. The downfield region of the PMR spectrum showed signals of a 4H AA′XX′ system at δ 6.86 (d, J = 8.5 Hz, H-2′/6′) and 6.73 (d, J = 8.5 Hz, H-3′/5′), which were parts of ring B of afzelechin [8]. Additionally, the spectrum allowed the identification of an ABX aromatic system for three aromatic protons that resonated at δ 6.62 (br.s, H-2‴), 6.81 (d, J = 8.5 Hz, H-5‴) and 6.48 (d, J = 8.5 Hz, H-6‴) and assigned to the catechin unit [9]. The characteristic signals in the 13C NMR spectra and the coupling constants of the sugar protons confirmed the presence of a β-glucopyranose unit in the structure. All the signals were identical to those reported in the literature for afzelechin-(4α→8″)-catechin-3-O-β-glucopyranoside (8) [10].

Based on the utilization in traditional medicine of A. tonkinensis extract as immunosuppressive drugs in the treatment of arthritis, and since the isolated compound 1 (maesopsin 4-O-β-D-glucopyranoside), which was the most abundant isolated compound, significantly inhibited the proliferation of activated T lymphocytes and up-regulated the HMOX1, SRXN1, and BCAS3 genes in acute myeloid leukemia [3], we tested the effects of compound 8 on cell growth of two hematologic tumor cell lines: OCI-AML and Jurkat (T cell lymphoma). The results showed that it had no cell growth inhibitory activity on the reported cancer cell lines.

The three compounds 6–8 are reported for the first time in the genus Artocarpus, and proanthocyanidin glucoside 8 is proved to occur in nature for the second time.

Afzelechin-(4 α →8″)-catechin-3- O - β -D-glucopyranoside (8). Amorphous yellow semisolid. HR-ESI-MS m/z 747.1885 [M + Na]+ and m/z 725.2077 [M + H]+. PMR (500 MHz, D2O, δ, ppm, J/Hz): 6.86 (2H, d, J = 8.8, H-2′, 6′), 6.81 (1H, d, J = 8.5, H-5‴), 6.73 (2H, d, J = 8.8, H-3′, 5′), 6.62 (1H, br.s, H-2‴), 6.48 (1H, d, J = 8.5, H-6‴), 6.09 (0.7H, br.s, H-6″), 5.94 (0.7H, br.s, H-6), 5.70 (0.7H, br.s, H-8), 4.42 (1H, br.d, J = 9.0, H-2″), 4.41 (1H, br.d, J = 7.0, H-3), 4.35 (1H, br.d, J = 9.5, H-2), 4.32 (1H, br.d, J = 7.0, H-4), 3.74 (1H, q, J = 8.0, H-3″), 3.44 (2H, br.s, Glc H-6), 3.27 (1H, br.d, anomeric H-1), 3.16 (1H, t, J = 9.0, Glc H-4), 2.97 (1H, d, J = 9.0, Glc H-5), 2.92 (1H, t, J = 9.5, Glc H-2), 2.81 (1H, dd, J = 6.0, 16.0, H-4″A), 2.75 (1H, br.d, J = 9.5, Glc H-3), 2.40 (1H, dd, J = 9.0, 16.0, H-4″B). 13C NMR (125 MHz, D2O, δ, ppm): 157.8 (C-9), 157.3 (C-4′), 156.3 (C-7), 155.9 (C-5), 154.9 (C-5″), 154.8 (C-9″), 154.2 (C-7″), 145.4 (C-4‴), 145.1 (C-3‴), 131.9 (C-1‴), 131.3 (C-1′), 130.9 (C-2′, 6′), 121.7 (C-6‴), 117.1 (C-5‴), 116.70 (C-2‴), 116.66 (C-3′, 5′), 110.8 (C-8″), 108.2 (C-10), 103.1 (C-10″), 103.0 (Glc C-1), 96.75 (C-6), 96.80 (C-8), 82.4 (C-2″), 81.7 (C-2), 81.1 (C-3), 76.6 (Glc C-5), 76.3 (Glc C-3), 74.6 (Glc C-2), 70.4 (Glc C-4), 68.8 (C-3″), 62.2 (Glc C-6), 37.1 (C-4), 29.5 (C-4″).

Furthermore, compounds 1 and 2 are auronol glycosides occurring rarely in nature [11]. Thus, compounds 1, 2, and 8 could be valuable as taxonomic markers for A. tonkinensis [12]. Worth noting is the fact that this type of chemical constituents is only found in the leaves and is significantly different in the bark and roots of this species [2, 4, 12,13,14,15]. This could prove helpful in the chemosystematic investigation of the polar constituents of A. tonkinensis.