Synthesis and BK channel-opening activity of 2-amino-1,3-thiazole derivatives.

A series of 2-amino-5-arylmethyl- or 5-heteroarylmethyl-1,3-thiazole derivatives were synthesized and evaluated for BK channel-opening activities in cell-based fluorescence assay and electrophysiological recording. The assay results indicated that the activities of the investigated compounds were influenced by the physicochemical properties of the substituent at benzene ring.

Design, synthesis of novel C-3'-N-sulfonyl modified taxane analogues from 1-deoxybaccatin VI and their impact on anti-HCC activity.

A new series of C-3'-N-sulfonyl paclitaxel analogs were designed and synthesized from 1-deoxybaccatin VI and their structures were confirmed by 1H NMR, 13C NMR and high resolution MS. The synthesized compounds were evaluated for their in vitro anti-Hepatocellular carcinoma (HCC) activity against human hepatoma (HepG2) cell line. Bioassay results showed that compounds 17c, 17d and 17f exhibited more potent inhibitory activity against HepG2 cell line in comparison with paclitaxel. It is suggested that paclitaxel analogs containing the C-3'-N-sulfonyl could be considered as a precursor structure for further synthesis of more potent analogues.

Synthesis and biological evaluation of C-13, C-14 modified taxane analogues from 1-deoxybaccatin VI.

Four C-13, C-14 side chain modified 9(R)-hydroxy-1-deoxy-taxane analogues 15, 16, 19 and 22 were semi-synthesized from 1-deoxybaccatin VI. The in vitro antitumor activity of these compounds was evaluated against A549 and A2780 cell lines. The preliminary SAR analysis showed that introduction of oxygen-containing group on C-14 could improve the cytotoxic activities.

The synthesis and antistaphylococcal activity of N-sulfonaminoethyloxime derivatives of dehydroabietic acid.

A series of N-sulfonaminoethyloxime derivatives of dehydroabietic acid were synthesized and investigated for their antibacterial activity against Staphylococcus aureus Newman strain and multidrug-resistant strains (NRS-1, NRS-70, NRS-100, NRS-108 and NRS-271). Most of the target compounds having chloro, bromo, trifluoromethyl phenyl moiety exhibited potent in vitro antistaphylococcal activity. The meta-CF3 phenyl derivative T23 showed the highest activity with MIC of 0.39-0.78 µg/mL against S. aureus Newman, while several analogues showed similar potent antibacterial activity with MIC values between 0.78 and 1.56 µg/mL against five multidrug-resistant S. aureus. The stability of T35 in plasma of SD rat and the cellular cytotoxicity were also evaluated.

Synthesis and biological evaluation of novel A-seco-taxoids derived from 1-deoxybaccatin VI.

Three novel nor-seco-taxoids 13, 15, 23 in which the A rings are cleaved but the B, C, and D rings are retained were prepared from 1-deoxybaccatin VI via its nor-dioxo derivative and their structures were confirmed by 1H NMR, 13C NMR and high resolution MS. Oxidative introduction of C-1 hydroxyl to 1-deoxybaccatin VI with oxidising agent KBrO3 and catalyst RuCl3 led to the dioxo derivative 6 and its structure is determined by X-ray crystallographic analysis. A-seco taxoids 13, 15, 23 with a C-13 ester linkage were tested for cytotoxic activity and all compounds showed no measurable cytotoxic activity against HCT-116 cell line. However, 1-deoxy-9a-dihydrotaxane analogue 4 semi-synthesised from 1-deoxybaccatin VI is 10-fold less cytotoxic than paclitaxel, indicating the indispensible nature of the A ring double bond for the bioactivity of paclitaxel.

The synthesis and antistaphylococcal activity of dehydroabietic acid derivatives: modifications at C12 and C7.

A series of 7-N-acylaminoethyl/propyloxime derivatives of dehydroabietic acid were synthesized and investigated for their antibacterial activity against Staphylococcus aureus Newman strain and multidrug-resistant strains (NRS-1, NRS-70, NRS-100, NRS-108 and NRS-271). Most of the target compounds having trifluoromethyl phenyl/benzyl, halogen-substituted thiophenyl, benzothiophenyl or pyrrolyl moiety exhibited potent in vitro antibacterial activity. Among which, compounds 4m, 4x and 7j showed high antibacterial activity with minimum inhibitory concentration (MIC) values of 1.25-3.13 µg/mL against five multidrug-resistant S. aureus.

Synthesis and anti-inflammatory evaluation of novel paclitaxel analogs.

A series of paclitaxel analogs modified at C-3'-N and C-7 positions were synthesized from baccatin III and their structures were confirmed by 1H-NMR, 13C-NMR, HR-MS. Compound 7e exhibited potent ability to decrease TNFα (tumor necrosis factor α) in the LPS-activated RAW264.7 murine macrophage-like cell line. The preliminary data indicated that the anti-inflammatory effects may be related to MD-2 and Toll-like receptor 4 (TLR4), rather than Toll-like receptor 2 (TLR2).

The synthesis and antistaphylococcal activity of dehydroabietic acid derivatives: Modifications at C-12.

A series of 12-oxime and O-oxime ether derivatives of dehydroabietic acid were synthesized and investigated for the antibacterial activity against Staphylococcus aureus Newman strain and five multidrug-resistant strains (NRS-1, NRS-70, NRS-100, NRS-108, and NRS-271). The aromatic oximate derivative 11a showed the highest activity with MIC of 0.39-0.78µg/mL against S. aureus Newman. Of note, compounds 10b, 11 and 14 showed the most potent antibacterial activity against five multidrug-resistant S. aureus with MIC values of 1.25-3.13µg/mL. These results offered useful information for further strategic optimization in search of the antibacterial candidates against infection of multidrug-resistant Gram-positive bacteria.

The synthesis and BK channel-opening activity of N-acylaminoalkyloxime derivatives of dehydroabietic acid.

A series of N-acylaminoalkyloxime derivatives of dehydroabietic acid were synthesized and evaluated for BK channel-opening activities in an assay system of CHO-K1 cells expressing hBKα channels. The structure-activity relationship study revealed that a non-covalent interaction between the S atom of the 2-thiophene and the carbonyl O atom may contribute to conformation restriction for interaction with the ion channel. This research could guide the design and synthesis of novel abietane-based BK channel opener.

Syntheses and biological evaluation of C-3'-N-acyl modified taxane analogues from 1-deoxybaccatin-VI.

A series of side-chain modified taxane analogues were synthesized and their in vitro anticancer activities against four human cancer cell lines: MDA-MB-231 (human breast cancer), PC-3 (human prostatic cancer), HepG2 and H460 (human hepatoma) were studied. The three hydroxyl groups at C-7, C-9 and C-10 enable the behavior of these compounds to be evidently distinct from other similar compounds. The strong cytotoxicity in the four cell lines showed by the newly synthesized taxane analogues 13a and 13d indicated them as potential lead compounds for anticancer drug design.

Semi-synthesis of 1-deoxypaclitaxel and its analogues from 1-deoxybaccatin VI.

Despite numerous synthetic efforts and extensive SAR studies on paclitaxel analogs, little work has been devoted to derive SAR of the C-1 hydroxy group. Up to now, 1-deoxypaclitaxel has only been reported to be isolated from the Chinese yew, Taxus mairei (Taxaceae). However, the isolation from natural sources does not solve the availability problem due to the reported low yield of isolation. Also, only several analogues of this type have been reported. Thus, there is an urgent need for exploration of new synthetic methods on this structurally intriguing molecule and further SAR studies. In present work, we report the initial expedient semi-synthesis of 1-deoxypaclitaxel and its novel analogues with structural variations at C7 and C10 from 1-deoxybaccatin VI, as well as their cytotoxic activities against A 549 cell line.

Molecular mechanism of pharmacological activation of BK channels.

Large-conductance voltage- and Ca(2+)-activated K(+) (Slo1 BK) channels serve numerous cellular functions, and their dysregulation is implicated in various diseases. Drugs activating BK channels therefore bear substantial therapeutic potential, but their deployment has been hindered in part because the mode of action remains obscure. Here we provide mechanistic insight into how the dehydroabietic acid derivative Cym04 activates BK channels. As a representative of NS1619-like BK openers, Cym04 reversibly left-shifts the half-activation voltage of Slo1 BK channels. Using an established allosteric BK gating model, the Cym04 effect can be simulated by a shift of the voltage sensor and the ion conduction gate equilibria toward the activated and open state, respectively. BK activation by Cym04 occurs in a splice variant-specific manner; it does not occur in such Slo1 BK channels using an alternative neuronal exon 9, which codes for the linker connecting the transmembrane segment S6 and the cytosolic RCK1 domain--the S6/RCK linker. In addition, Cym04 does not affect Slo1 BK channels with a two-residue deletion within this linker. Mutagenesis and model-based gating analysis revealed that BK openers, such as Cym04 and NS1619 but not mallotoxin, activate BK channels by functionally interacting with the S6/RCK linker, mimicking site-specific shortening of this purported passive spring, which transmits force from the cytosolic gating ring structure to open the channel's gate.

Design, synthesis, and characterization of BK channel openers based on oximation of abietane diterpene derivatives.

Oxime ether derivatives at the benzylic position of unsubstituted, dichloro, trichloro, and monobromo derivatives of the aromatic C-ring of dehydroabietic acid and podocarpic acid were synthesized and evaluated as BK channel openers in an assay system of CHO-K1 cells expressing hBKα channels. Detailed SAR analysis showed that the oximation was particularly effective in the cases of dehydroabietic acid derivatives, and some of these oxime derivatives showed more potent BK channel activities than the standard compound, NS1619. The present studies provide a new structural basis for development of efficient BK channel openers.

Novel oxime and oxime ether derivatives of 12,14-dichlorodehydroabietic acid: design, synthesis, and BK channel-opening activity.

Oxime ether derivatives of the benzylic ketone of 12,14-dichlorodehydroabietic acid (diCl-DHAA, 4b) were synthesised, and their BK channel-opening activity was evaluated in an assay system of CHO-K1 cells expressing hBKalpha channels. Oxime ether structure on the B ring of diCl-DHAA significantly increased the BK channel-opening activity.

Design, synthesis and characterization of podocarpate derivatives as openers of BK channels.

We found that the podocarpic acid structure provides a new scaffold for chemical modulators of large-conductance calcium-activated K(+) channels (BK channels). Structure-activity analysis indicates the importance of both the arrangement (i.e., location and orientation) of the carboxylic acid functionality of ring A and the hydrophobic region of ring C for expression of BK channel-opening activity.

Novel BK channel openers containing dehydroabietic acid skeleton: structure-activity relationship for peripheral substituents on ring C.

A series of dehydroabietic acid (DHAA, 2) derivatives was synthesized and evaluated as BK channel openers in an assay system of CHO-K1 cells expressing hBKalpha channels. Systematic modifications of the peripheral functionality of ring C of DHAA showed that the introduction of a nitro or (thio)urea group in ring C greatly enhanced the BK channel-opening activity.

Total synthesis of the originally proposed and revised structures of scleritodermin A.

The first total synthesis of the originally proposed and revised structure of scleritodermin A, along with an isomer, were achieved by the use of an alpha-azido carboxyl group serving as the key alpha-ketoamide precursor, thus leading to a revision of the structure originally proposed for natural scleritodermin A.

Identification of potent type I MetAPs inhibitors by simple bioisosteric replacement. Part 2: SAR studies of 5-heteroalkyl substituted TCAT derivatives.

Systematic SAR studies on the thiazole ring 5-substituent of TCAT derivatives revealed that the introduction of a beta-alkoxy or an amino group enhanced the inhibitory activity significantly. The present compounds are representative of specific Co(II)-MetAP1 inhibitors. Before the physiologically relevant metal ions for MetAPs are established, these small molecular compounds could be used as tools for detailed biological studies.

Identification of potent type I MetAP inhibitors by simple bioisosteric replacement. Part 1: Synthesis and preliminary SAR studies of thiazole-4-carboxylic acid thiazol-2-ylamide derivatives.

A series of thiazole-4-carboxylic acid thiazol-2-ylamide (TCAT, 4) derivatives were designed and synthesized according to simple bioisosteric replacement from previously reported pyridine-2-carboxylic acid thiazol-2-ylamide (PCAT) MetAP inhibitors. The preliminary SAR studies demonstrated that these TCAT series of compounds showed different activity and selectivity compared with those of the corresponding PCAT compounds. These findings provide useful information for the design and discovery of more potent inhibitors of type I MetAPs.

Characterization of full length and truncated type I human methionine aminopeptidases expressed from Escherichia coli.

Methionine aminopeptidase (MetAP) carries out an essential posttranslational modification of nascent proteins by removing the initiator methionine and is recognized as a potential target for developing antibacterial, antifungal, and anticancer agents. We have established an Escherichia coli expression system for human type I MetAP (HsMetAP1) and characterized the full length HsMetAP1 and its N-terminal-truncated mutants HsMetAP1(Delta1-66) and HsMetAP1(Delta1-135) for hydrolysis of several thiopeptolide and peptide substrates and inhibition by a series of nonpeptidic inhibitors. Although the N-terminal extension with zinc finger motifs in HsMetAP1 is not required for enzyme activity, it has a significant impact on the interaction of the enzyme with substrates and inhibitors. In hydrolysis of the thiopeptolide substrates, a relaxation of stringent specificity for the terminal methionine was observed in the truncated mutants. However, this relaxation of specificity was not detectable in hydrolysis of tripeptide or tetrapeptide substrates. Several nonpeptidic inhibitors showed potent inhibition of the mutant HsMetAP1(Delta1-66) but exhibited only weak or no inhibition of the full length enzyme. With the recombinant HsMetAP1 available, we have identified several MetAP inhibitors with submicromolar inhibitory potencies against E. coli MetAP (EcMetAP1) that do not affect HsMetAP1. These results have demonstrated the possibility of developing MetAP inhibitors as antibacterial agents with minimum human toxicity. In addition, micromolar inhibitors of HsMetAP1 identified in this study can serve as tools for investigating the functions of HsMetAP1 in physiological and pathological processes.