Synthesis of 1-O-acyl- and 1-oxo-kamebanin analogues and their cytotoxic activity.

A series of 1-O-acyl- and 1-oxo-kamebanin analogues were prepared from kamebanin, isolated from Rabdosia excisa and their cytotoxicity was assayed on HL60 promyelocytic leukemia cells and HCT116 human colon cancer cells. The structure-activity relationship study showed that the presence of 1-O-acyl groups of a C3-C5 carbon chain increased the cytotoxic activity.

Estrogenic phytochemical from Labisia pumila (Myrsinaceae) with selectivity towards estrogen receptor alpha and beta subtypes.

Labisia pumila var. alata (Myrsinaceae) or "Kacip fatimah" is a famous Malay traditional herb used for the maintenance of women's health. The extracts of L.pumila displayed estrogenic activity in rats. Nonetheless, the estrogenic bioactives were not identified. The aim of the study is to identify estrogenic compounds contributing to the established estrogenic activity. Bioactivity-guided-isolation method guided the isolation of pure bioactives. The hexane extract was subjected to a series of silica gel flash and open column chromatography with increasing amount of ethyl acetate in hexane or methanol in chloroform. Each fraction or pure compounds were evaluated on it's estrogen receptor (ER) binding activity with the fluorescence polarization competitive ERα and ERß binding assay kit. Cytotoxic assay using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay method was used to establish the cytotoxic activity of the compounds. Four alkyl resorcinols and a dimeric 1,4-benzoquinone, namely belamcandol B (1), 5-pentadec-10'-(Z)-enyl resorcinol (2), 1,3-dihydroxy-5-pentadecylbenzene (3), 5-(heptadec-12'-(Z)-enyl) resorcinol (4) and demethylbelamcandaquinone B (5) were identified with selective binding affinities towards either ERα or ERß exhibiting selectivity ratio from 0.15-11.9. Alkyl resorcinols (2)-(4) exhibited cytotoxic activity towards HL60 cells with IC50 values from 19.5-22.0 µM. Structural differences between compounds influence the binding affinities to ER subtypes. Further study is needed to establish the agonist or antagonist effect of these compounds on various tissues and to identify if these compounds exert cytotoxic activity through the ERs. When consuming L.pumila as a complementary medicine, careful consideration regarding it's estrogenic compound content should be given due consideration.

RA-XXV and RA-XXVI, Bicyclic Hexapeptides from Rubia cordifolia L.: Structure, Synthesis, and Conformation.

Two RA-series bicyclic hexapeptides, RA-XXV (4) and RA-XXVI (5), which have no N-methyl group at Tyr-5, were isolated from the roots of Rubia cordifolia L. Their amino acid compositions and sequences were determined by interpretation of MS, and 1D and 2D NMR data and their relative structures were elucidated by XRD analysis of 4 and RA-XXVI acetate (6). The absolute stereochemistry of 4 was established by the total synthesis of 4, and that of 5, by the chemical correlation with 4. Peptides 4 and 5 exhibited cytotoxicity toward human promyelocytic leukemia HL-60 (IC50 =0.062 and 0.066 µm, respectively) and human colonic carcinoma HCT-116 (IC50 =0.028 and 0.051 µm, respectively) cell lines. Analysis of the conformational structures of 4 and 6 in the crystalline state and those of 4 and 5 in solution revealed that the N-methyl group at Tyr-5 functions to make this series of peptides preferentially adopt the active conformation.

Aza-cycloisodityrosine analogue of RA-VII, an antitumor bicyclic hexapeptide.

An aza-cycloisodityrosine analogue of RA-VII, 3, was designed and synthesized. The key aza-cycloisodityrosine unit was prepared by copper(II)-acetate-mediated intramolecular phenylamine/arylboronic acid coupling of dipeptide followed by connection with the tetrapeptide segment to afford a hexapeptide. Subsequent macrocyclization of the hexapeptide with EDC · HCl and HOOBt under dilute conditions gave 3. Analogue 3 showed significant cytotoxic activity against human promyelocytic leukemia HL-60 cells and human colon carcinoma HCT-116 cells, but its activity was weaker than that of parent peptide RA-VII (1).

Abietane diterpenoids and a sesquiterpene pyridine alkaloid from Euonymus lutchuensis.

Four new abietane diterpenoids (1-4), a new 9(10→20)-abeo-abietane diterpenoid (5), and a new sesquiterpene pyridine alkaloid (6) were isolated from the roots of Euonymus lutchuensis along with 19 known compounds. The structures of the new compounds were elucidated by interpretation of the spectroscopic data.

Goniolandrene A and B from Goniothalamus macrophyllus.

Goniothalamus macrophyllus (Blume) Hook. f. & Thoms. is a plant widely distributed in Malaysia. The aim of this study is to identify compounds from the roots of G. macrophyllus. The ground roots were extracted with aqueous methanol and partitioned sequentially with n-hexane, chloroform and butanol. Purification from this extracts afforded six compounds with two new compounds, namely goniolandrene-A (1), -B (2). The absolute configuration of goniolandrene B (2) was established by circular dichrosim. The compounds were cytotoxic against the P388 cells with IC50 values ranging from 0.42 to 160 µM. Goniothalamin (3) exhibited the highest inhibition of 0.42 µM.

Synthesis of [Tyr-5-Ψ(CH2NMe)-Tyr-6]RA-VII, a reduced peptide bond analogue of RA-VII, an antitumor bicyclic hexapeptide.

A reduced peptide bond analogue of RA-VII, [Tyr-5-Ψ(CH(2)NMe)-Tyr-6]RA-VII (3), was designed and synthesized. The key reduced cycloisodityrosine unit was prepared by reduction of the cycloisodityrosine derived from natural RA-VII, followed by connection with the tetrapeptide segment to afford a hexapeptide. Subsequent macrocyclization of the hexapeptide with FDPP under dilute conditions gave 3. Analogue 3 showed cytotoxic activity against P-388 cells, but its activity was much weaker than that of parent peptide RA-VII.

Isolation, structure determination, and synthesis of allo-RA-V and neo-RA-V, RA-series bicyclic peptides from Rubia cordifolia L.

Two bicyclic hexapeptides, allo-RA-V (4) and neo-RA-V (5), and one cyclic hexapeptide, O-seco-RA-V (6), were isolated from the roots of Rubia cordifolia L. Their gross structures were elucidated on the basis of spectroscopic analysis and X-ray crystallography of compound 5. The absolute stereochemistry of compounds 4 and 5 were established by their total syntheses, and the absolute stereochemistry of compound 6 by chemical correlation with deoxybouvardin (3). Comparison of the 3D structures of highly active RA-VII (1) with less-active compounds 4 and 5 suggests that the orientation of the Tyr-5 and/or Tyr-6 phenyl rings plays a significant role in their biological activity. The isolation of peptides 4-6, along with compound 3, and the comparison of their structures seem to indicate that peptide 6 may be the common precursor to bicyclic peptides 3-5 in the plant.

Monoclonal antibodies from Rubia cordifolia against antitumor cyclohexapeptide deoxybouvardin and their use in immunoassay.

An immunoassay system was established for the estimation of the quantity of an antitumor cyclohexapeptide, deoxybouvardin (RA-V) from Bouvardia ternifolia (Cav.) Schlecht, Rubia cordifolia L., and R. akane Nakai (Rubiaceae). First, RA-V was converted into a protein conjugate to make it an effective antigen. In the conjugate the molecular ratio between RA-V and the carrier protein was 5.9:1. The splenocytes from the mouse immunized with the conjugate were then fused with mouse myeloma cells to produce hybridoma, secreting monoclonal antibodies (MAbs) against RA-V. Two clones were isolated, one producing MAb IgG(1) and the other MAb IgG(2b), both having a κ light chain. The resultant MAbs were evaluated for their sensitivity and cross-reactivity.

Semisynthesis of triptolide analogues: effect of γ-lactone and C-14 substituents on cytotoxic activities.

Triptolide γ-lactone and C-14 analogues were prepared and evaluated cytotoxity against human lung adenocarcinoma epithelial A549 cells and human colon adenocarcinoma HT-29 cells. γ-Lactone substructure and C-14 substituents affected the biological activities significantly.

Production of monoclonal antibodies against antitumor cyclohexapeptide RA-VII from Rubia cordifolia and their characterization.

An immunoassay system was established for the estimation of the quantity of an antitumor cyclic hexapeptide RA-VII (1) from Rubia cordifolia L. and R. akane Nakai (Rubiaceae). First, 1 was converted into its hapten, which was then conjugated with a carrier protein to be used as an effective antigen to obtain its monoclonal antibody (MAb). In the resulting conjugate, the molecular ratio between 1 and the carrier protein as assayed by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) was about 5:1. Then, the splenocytes from the mouse immunized with the conjugate were fused with mouse myeloma cells to produce hybridoma, secreting MAb against 1. Two clones were isolated, one producing MAb IgG(1) and the other IgM, both having a κ light chain. The sensitivity and cross-reactivity of the thus obtained MAb were also assayed.

Fluorination of triptolide and its analogues and their cytotoxicity.

The reaction of triptolide and its analogues with a fluorinating agent, that is, bis(2-methoxyethyl)aminosulfur trifluoride (Deoxo-Fluor) or (diethylamino)sulfur trifluoride (DAST), was studied. One of the fluorinated products, 14beta-dehydroxy-14beta-fluoro triptolide, was found to be more cytotoxic than the parent natural triptolide.

A novel bicyclic hexapeptide, RA-XVIII, from Rubia cordifolia: structure, semi-synthesis, and cytotoxicity.

A new bicyclic peptide of RA-series, RA-XVIII (3), was isolated from the roots of Rubia cordifolia L. Its structure was established to be a hydroxylated derivative of RA-VII by the semi-synthesis of 3 from deoxybouvardin, and its cytotoxicity against P-388 cells was 0.012 microg/mL.

Tricalysiamides A-D, diterpenoid alkaloids from Tricalysia dubia.

Four rearranged ent-kaurane diterpenoid alkaloids, tricalysiamides A-D (1-4), having a cafestol-type carbon framework were isolated from the wood of Tricalysia dubia. Their absolute structures were determined on the basis of 2D NMR spectroscopy, X-ray crystallographic analysis, and chemical methods.

Synthesis of 1-O-monoacyl or 12-O-monoacyl, 1-,12-O-diacyl-, and 11,12-dehydrated excisanin A 7,14-acetonides and their cytotoxic activity.

1-O-Monoacyl, 12-O-monoacyl, 1-,12-O-diacyl, and 11,12-dehydrated excisanin A 7,14-acetonides were synthesized from excisanin A isolated from Rabdosia excisa. The structure and cytotoxic activity relationships (SAR) of the natural parent ent-kaurene diterpenes and these semisynthetic analogues were studied by using P388 murine leukemia cells.

Semisynthesis of C-ring modified triptolide analogues and their cytotoxic activities.

Several C-ring modified analogues of a potent antileukemic diterpene, triptolide (1), were synthesized and their structure-activity relationships were studied.

New quassinoids, javanicolides C and D and javanicosides B--F, from seeds of Brucea javanica.

Two new quassinoids, javanicolides C and D, and five new quassinoid glucosides, javanicosides B-F, were isolated from the seeds of Brucea javanica, along with eight known quassinoids, i.e., yadanziolides A, C, D, and S, bruceins D and E, brusatol, and the aglycone of yadanzioside D, and 19 known quassinoid glucosides, i.e., yadanziosides A-G, I, and K-P, bruceosides A-C and E, and bruceantinoside A. Their structures were elucidated by analysis of spectroscopic data and chemical evidence.

Semisynthesis of an analogue of antitumor bicyclic hexapeptide RA-VII by fixing the Ala-2/Tyr-3 bond to Cis by incorporating a triazole cis-amide bond surrogate.

We prepared an analogue of an antitumor bicyclic hexapeptide RA-VII whose amide configuration between residues 2 and 3 was fixed to cis by incorporating a triazole cis-amide bond surrogate. This analogue was shown, by NMR studies, to take almost the same conformation as that of the minor conformer of RA-VII. It showed no cytotoxic activity.

Excisanin H, a novel cytotoxic 14,20-epoxy-ent-kaurene diterpenoid, and three new ent-kaurene diterpenoids from Rabdosia excisa.

A novel 14,20-epoxy-ent-kaurene diterpenoid, excisanin H (1), and three new ent-kaurene diterpenoids, 2-4, were isolated from aerial parts of Rabdosia excisa along with eight known ent-kaurene diterpenoids, 5-12. The structural elucidations were made using spectral (HREIMS, IR, (1)H, (13)C, and 2D NMR) methods. The absolute configuration of 1 was determined by demonstrating that oxidation of kamebakaurin (8) produced excisanin H (1). These ent-kaurene diterpenoids all showed significant cytotoxic activity against P388 murine leukemia cells.

Synthesis of [Gly-1]RA-VII, [Gly-2]RA-VII, and [Gly-4]RA-VII. Glycine-containing analogues of RA-VII, an antitumor bicyclic hexapeptide from Rubia plants.

Three analogues of RA-VII (1), an antitumor bicyclic hexapeptide from Rubia plants, were synthesized. Three analogues, [Gly-1]RA-VII (4), [Gly-2]RA-VII (5), and [Gly-4]RA-VII (6), in which one of the three alanine residues in 1 was replaced by a glycine residue, were prepared by linking of the cycloisodityrosine unit, obtained by degradation of 1, to three different glycine-containing tetrapeptides followed by macrocyclization. Of these three analogues, analogue 4 showed the highest cytotoxic activity. The NMR study revealed that in solution the conformer structures and their ratios of analogue 4 were very similar to those of natural peptide 1, suggesting that the methyl groups at Ala-2 and Ala-4 should be essential for producing the bioactive conformation, whereas that at D-Ala-1 is not essential.