Tran Van Loc

Synthesis of Amino Acid Conjugates and Further Derivatives of 3α-Hydroxylup-20(29)ene-23,28-dioic acid

Triterpenes of betulinic acid type exhibit many interesting biological activities. Therefore a series of new 3α-hydroxy-lup-20(29)-ene-23,28-dioic acid derivatives 2a—22 with putative pharmacological activities were synthesized. As starting compounds 3α-hydroxy-lup-20(29)-ene-23,28-dioic acid (1a), isolated from Schefflera octophylla, or its 3-O-acetyl derivative 1b were used. Mono- and diesters (2a—b from 1a, and 4d from 4c) were prepared with CH2N2. Oxidation of the isopropenyl side chain with OsO4 yielded the 20,29-diols (4a—b from 1b, and 19 from 17), which were in the case of 4b further transformed to the 29-norketones 8a/mdash;b. Oxidation of the isopropenyl side chain with m-chloroperbenzoic acid afforded the 20,29-epoxide 12 (from 1b) and the 29-aldehydes and a-hydroxy aldehydes (13a—c from 2a, 14a—c from 2b, and 16a—c from 15a). Ring A was modified by a tosylation—elimination sequence using p-TsCl/NaOAc, which afforded diolefin 15a (from 2a) with Δ2,20(29) double bonds or 23-nor-Δ3,20(29)diolefin 17 (from 1a). Compounds 4b, 4c, and 8a were coupled with L-methionin, L-phenylalanin, L-alanin, L-serin, and L-glutaminic acid via amide bonds at positions 23 and 28 to afford the amino acid conjugates 5a—7b and 9a—11.

Synthesis of madecassic acid derivatives and their cytotoxic activity

Abstract Fifteen new 28-amide derivatives of madecassic acid, isolated from the tropical medicinal herb Centella asiatica (Apiaceae), have been synthesised, and their cytotoxicity on three cancer cell lines, KB (carcinoma cancer), HepG2 (liver cancer) and Lu-1 (lung cancer), was evaluated. The results showed that acetylation of the 2,3,23-hydroxyl group and/or amidation of the 28-COOH group strongly increased the cytotoxicity of the synthesised compounds.

Two new prenylated isoflavones from Maclura cochinchinensis collected in Hoa Binh province Vietnam

Abstract Two new prenylisoflavones, 3′,4′,5-trihydroxy-8-prenyl-dihydrofuran[2″,3″:7,6]isoflavone (1) and 4′,5-dihydroxy-8-prenyl-dihydrofuran[2″,3″:7,6]isoflavone (2), along with five known prenylisoflavones (3–7), benzylalcohol-4-O-β-d-glucoside (8) and two cinnamic acid esters (9, 10) were isolated from the leaves of Maclura cochinchinensis (Cudrania cochinchinensis). Their structures were elucidated by analysis of NMR (1H-, 13C-NMR, HSQC, HMBC), MS spectra and comparison with the published data. Compounds 4–10 were the first time isolated from this species. Prenylisoflavones 1–4 and 6–7 were evaluated for their in vitro cytotoxic activity on KB and HepG2 cancer cell lines. Compound 4 showed cytotoxic activity against both cancer cell lines with IC50 values of 26.99 and 19.95 μM, respectively. The other compounds were considered as inactive.

The Alkaloidal Constituents of Cephalotaxus mannii Collected in Lam Dong Province, Vietnam

Eight alkaloidal constituents have been isolated and structurally elucidated from Cephalotaxus mannii Hook. f. collected from the highland Lam Dong Province, Vietnam. They are: cephalotaxine (1), isoharringtonine (2), norisoharringtonine (3), desoxyharringtonine (4), nordesoxyharringtonine (5), cephalotaxine 𝛽 -N-oxide (6), 3-epi-schellhammericine (7), and an isomer of 3-epi-schellhammericine (8). Among them, norisoharringtonine (3) is a new compound, while the other compounds are isolated from C. mannii for the first time. The structures of these constituents were determined by spectroscopic methods such as FTIR, ESI-MS, HR-ESI-MS, and NMR (1D, 2D) and by comparison with published data.

The non-alkaloidal constituents of Cephalotaxus mannii, collected in Lam Dong province

Three non-alkaloidal constituents: harringtonolide (nor-diterpene lactone), epicatechin and epigallocatechin have been isolated from Cephalotaxus mannii, collected in Lam Dong province, Vietnam in the frame work of the Tay Nguyen program III (TN III-15). Their structures were elucidated by the spectroscopic methods as the IR, ESI-MS, HR ESI-MS and NMR (1D, 2D) spectroscopy and comparison with published data. This is the first report of these compounds from Cephalotaxus mannii. Keywords. Cephalotaxus mannii, harringtonolide, epicatechin, epigallocatechin.

Chemical study of the leaves of Lagerstroemia speciosa in Vietnam

The main constituents of the EtOH extract of leaves of Lagerstroemia speciosa supplied by Traphaco company have been quantitatively determined by HPLC to be corosolic acid (2.242 %), asiatic acid (1.219 %) and β-sitosterol. Repeated column chromatography of the n -hexane, ethyl acetate and dichloromethane extract of these leaves led to the isolation of corosolic acid, asiatic acid, quercetin, β-sitosterol and β-sitosterol-3-O-β-D-glucopyranosyl glucoside. The structures of these compounds have been elucidated by the IR, MS and NMR spectral analysis.

Triterpenes and phytosterols from Scaevola taccada collected in Ly Son island, Quang Ngai province, Vietnam

From the ethyl acetate extract of the leaves of Scaevola taccada (Gaertn.) Roxb., two triterpenes (ursolic acid 6 , myricadiol 5 ), two sterols (β-sitosterol 3 , β-sitosterol glycoside 4 ), together with two long-chain hydrocarbons, tritriacontane 1 and tetracosane 2 have been isolated. Their structures were elucidated by the analysis of the IR, MS and NMR 1D and 2D spectra. Compound 1 , 2 , 3 , 5 , 6 were isolated for the first time from Scaevola taccada .

Chemical constituents of the barks of Litsea glutinosa collected in Thai Nguyen province, Vietnam

From the ethyl acetate extract of the barks of Litsea glutinosa four compounds including cis -5,8,11,14,17-eicosapentaenoic acid methyl ester ( 1) , spatozoate ( 2) , betasitosterol ( 3) and daucosterol ( 4) have been isolated. Compound ( 5 ) 1-heptadecanol, compound ( 6 ) 1-eicosanol and compound ( 7 ) glycerol 1,3-di-(9Z,12Z-octadecadienoate) 2-hexadecanoate were isolated from the n -hexane extract. Their structures were elucidated by the analysis of the IR, MS and NMR spectra. Compounds ( 1 ), ( 2 ), ( 5 ), ( 6 ), ( 7 ) were isolated for the first time from Litsea glutinosa . Keywords. Litsea glutinosa , cis -5,8,11,14,17-eicosapentaenoic acid methyl ester, spatozoate, betasitosterol, daucosterol, 1-heptadecanol, 1-eicosanol, glycerol 1,3-di-(9Z,12Z-octadecadienoate) 2-hexadecanoate.

A new analog of δ-tocopherol from Livistona halongensis, a novel species discovered in ha long bay of Vietnam

Livistona is a genus with 36 species of palms native to southern Asia, Australia, and Africa [1]. Four species have been described to be in Vietnam [2]. The new species Livistona halongensis T. H. Nguyen & Kiew (Arecacea) was discovered (in 2000) in Ha Long Bay, one of the world s new seven natural wonders [3]. It is one of seven endemic plant species of the Ha Long area. There are no phytochemical and biological studies previously reported on this species. During our phytochemical investigation of Livistona halongensis, a new -tocopherol analog 1, 6-O-acetyl-2R,8-dimethyl-2-(4R,8R,11-trimethyltridecene12)chroman, together with four known triterpenes and two sterols 2–7, were isolated for the first time from the n-hexane extract of its roots and barks. Livistona halongensis roots and barks were collected in Ha Long Bay, Quang Ninh Province, Vietnam, in June 2009 and authenticated by Dr. Tran Thi Phuong Anh, Institute of Ecology and Biological Resources, Hanoi, Vietnam Academy of Science and Technology. A voucher specimen (No. NTH 2630) was deposited in this Institute. The dried and powdered roots (0.9 kg) and barks (2.5 kg) of L. halongensis were extracted with 80% aqueous MeOH at room temperature. The aqueous MeOH extracts was evaporated in vacuo, and the residues were suspended in water and successively partitioned with n-hexane and CHCl3. The n-hexane extract of the roots (2.1 g) was subjected to silica gel column chromatography (CC) eluting with n-hexane–EtOAc (v/v 10:1, 8:2, 7:3) to give six fractions. The fourth fraction (150 mg) was further purified over a silica gel column eluting with n-hexane–EtOAc (v/v 98:2 to 70:30) to afford three fractions. It was difficult to purify the second fraction by column chromatography. Therefore, the acetylation of this fraction was carried out for better separation. The second fraction (60 mg) was stirred with 2.5 mL Ac2O–pyridine (1:1) at room temperature for 10 hours. The solvent was removed under reduced pressure, and the acetylated product was purified through silica gel CC eluting with n-hexane–EtOAc (150:1), affording compound 1 (10 mg). The n-hexane extract of the barks (10 g) was subjected to CC eluting with n-hexane–EtOAc (98:2 95:5) to yield 9 fractions. Fraction 1 (100 mg) was applied to silica gel CC eluting with n-hexane–EtOAc (98:2) to give compound 2 (50 mg). Fraction 2 (62 mg) was purified through silica gel CC with n-hexane–EtOAc (98:2) to give compound 3 (30 mg). Fraction 4 (40 mg) was subjected to silica gel CC eluting with n-hexane–EtOAc (95:5) to give compound 4 (28 mg). Purification of fraction 6 (56 mg) through repeated silica gel CC with n-hexane–EtOAc (95:5) gave compound 5 (36 mg). Compounds 6 (50 mg) and 7 (650 mg) were obtained by recrystallization of fractions 8 and 9, respectively (solvent system n-hexane–EtOAc, 1:1). The structure of compound 1 was established using IR, MS, NMR (1H, 13C, COSY, HMBC, HSQC) spectral data and comparison with literature reports.