Synthesis of new antimicrobial pyrrolo[2,1-a]isoquinolin-3-ones

The attractive structure of the pyrroloisoquinoline moiety, together with its potential antimicrobial activity, encouraged us to prepare six 8-substituted and seven 8,9-disubstituted-1,2,3,5,6,10b-hexahydropyrrolo[2,1-a]isoquinolin-3-ones in a few steps with good yields. We applied a convenient methodology via double intramolecular cyclization conducted by a Bischler-Napieralski cyclodehydration-imine reduction sequence, which is widely employed in the synthesis of isoquinoline alkaloids. Therefore, we synthesized three series of these pyrrolo[2,1-a]isoquinolin-3-ones characterized by the substituent at the 8-position or 8,9-positions of the aromatic ring: (a) different side chains are attached to an 8-OH group (series 1); (b) a chlorine atom is attached to the 8-position (series 2); and (c) 8- and 9-carbons are bearing an identical group (series 3). The compounds bearing a benzylic moiety at the 8-position, for example, 8-benzyloxy-pyrrolo[2,1-a]isoquinolin-3-one (1a) and 8-(4-fluorobenzyloxy)-pyrrolo[2,1-a]isoquinolin-3-one (1e), as well as, a 8-chloro-9-methoxy moiety including the 8-chloro-9-methoxy-pyrrolo[2,1-a]isoquinolin-3-one (2a), provided the most fungicide and bactericide agents, respectively.     

Design and campaign synthesis of pyridine-based histone deacetylase inhibitors

A lead benzamide, bearing a cyanopyridyl moiety (3), was identified as a potent and low molecular weight histone deacetylase (HDAC) inhibitor. Various replacements of the cyano group were explored at the C3-position, along with the exploration of solubility-enhancing groups at the C5-position. It was determined that cyano substitution at the C3-position of the pyridyl core, along with a methylazetidinyl substituent at the C5-position yielded optimal HDAC1 inhibition and anti-proliferative activity in HCT-116 cells.     

Synthesis and evaluation of 2-substituted 8-hydroxyadenines as potent interferon inducers with improved oral bioavailabilities

In order to create novel compounds which possess potent interferon (IFN) inducing activities with excellent oral bioavailabilities, a series of 8-hydroxyadenines, which have various alkoxy or alkylthio moieties at the adenine C(2)-position, were synthesized and evaluated. The introduction of hydrophobic groups was not considered to be effective for potentiating the IFN-inducing activity, but several compounds having hydrophilic groups were effective. Among the compounds tested, compound 13f induced IFN from the dosage of 0.03 mg/kg, which was approximately 100-fold more potent than that of Imiquimod, and showed an excellent oral bioavailability (F=40%) which was 10-fold improved over 5, a lead compound (F=4%).     

Nitro and amino substitution within the A-ring of 5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)dibenzo[c,h][1,6]naphthyridin-6-ones: influence on topoisomerase I-targeting activity and cytotoxicity

Recently, 5H-8,9-dimethoxy-5-(2-N,N-dimethylaminoethyl)-2,3-methylenedioxydibenzo[c,h][1,6]naphthyridin-6-one, 1, was identified as a TOP1-targeting agent with pronounced antitumor activity. In the present study, the effect on activity of substituting a single nitro or amino group in the A-ring in lieu of the methylenedioxy moiety of 1 was evaluated. The presence of either a nitro or amino substituent at the 4-position had a pronounced adverse affect on both TOP1-targeting activity and cytotoxicity. To a lesser extent, derivatives with a nitro or amino substituent at the 1-position were also less active than 1. Replacement of the methylenedioxy moiety of 1 with either a nitro or amino substituent at either the 2- and 3-position did result in analogues with potent TOP1-targeting activity and cytotoxicity.     

Structure-activity relationships for alpha-glucosidase inhibition of baicalein, 5,6,7-trihydroxyflavone: the effect of A-ring substitution

In order to estimate the effects of the A-ring hydroxyl group of baicalein (5,6,7-trihydroxyflavone, 1) on rat intestinal alpha-glucosidase inhibition, flavone, monohydroxyflavones, dihydroxyflavones, and methylated derivatives of 5,6,7-trihydroxyflavone were used for the structure-activity relationship (SAR) study. The importance of the 6-hydroxyl group of baicalein was validated for an exertion of the activity. And also, the tested flavones which lacked a hydroxyl substituent on any of positions 5, 6, or 7, showed no activity. Hence, the 5,6,7-trihydroxyflavone structure was concluded to be crucial for the potent inhibitory activity. In addition, an introduction of electron-withdrawing or electron-donating groups at position 8 of baicalein led to a dramatic decrease for activity, except for 8-fluoro-5,6,7-trihydroxyflavone, which carried a less bulky substituent on position 8. Hence, this result suggested that a sterically bulky substituent on C-8 of baicalein was detrimental for the activity regardless of its electronic nature. Through examining the inhibitory mechanism of baicalein against rat intestinal alpha-glucosidase, it was suggested to be a mixed type inhibition.     

Synthesis and antitumor evaluation of novel 5-substituted-4-hydroxy-8-nitroquinazolines as EGFR signaling-targeted inhibitors

The synthesis and biological activity of a series of novel 5-substituted-4-hydroxy-8-nitroquinazolines that may function as inhibitors of EGFR- and/or ErbB-2-related oncogenic signaling are described. These compounds were prepared by S(N)Ar reaction of 5-chloro-4-hydroxy-8-nitroquinazoline with alkyl or aryl amines, or alkyl alcohol as nucleophiles. Although the enzyme assay showed a weak inhibition effect against both EGFR and ErbB-2 tyrosine kinases, the cell-based antitumor activity turned out promising. Compounds having 5-anilino substituent exhibit high potency with 5-(4-methoxy)anilino-4-hydroxy-8-nitroquinazoline (1h) being the best dual EGFR/ErbB-2 inhibitors, which effectively inhibited the growth of both EGFR (MDA-MB-468, IC(50)<0.01microM) and ErbB-2 (SK-BR-3, IC(50)=13microM) overexpressing human tumor cell lines in vitro. More interestingly, the variation of the substituent(s) at the 3- and/or 4-position of the 5-anilino portion was found to modulate the selectivity and potency dramatically. However, compounds having an alkylamino or alkyloxy group at the 5-position of 4-hydroxy-8-nitroquinazolines are essentially inactive. These results are consistent with molecular modeling observations. This study was the first attempt to identify new structural types of dual EGFR/ErbB-2-related signaling inhibitors by incorporation of the anilino group at the 5-position of 4-hydroxy-8-nitroquinazolines' core structure, providing promising new templates for further development of potent inhibitors targeting both EGFR and ErbB-2 tyrosine kinases.     

黄芩素的结构修饰以及抗肿瘤活性研究

为了改善黄芩素的抗肿瘤活性。本实验以黄芩素为原料,对其进行结构修饰。首先通过mannich反应,在8位引入胺亚甲基,然后通过酰基化反应在7位(6位)酚羟基上引入不同的疏水性基团。并利用CCK-8法对目标化合物进行抗MCF-7肿瘤细胞的活性评价。结果合成得到了6个目标化合物,通过1HNMR、13CNMR、MS和化学手段相结合的方法确定了其结构,其中化合物2~6为新化合物。实验利用黄酮类邻二酚羟基的特性,通过与氯化锶的络合反应,巧妙而简单的确证了所得目标化合物的酯键是在化合物的7位羟基上。抗MCF-7肿瘤活性实验表明,在黄芩素8位上引入含氮原子的胺亚甲基后活性比先导化合物黄芩素强,在其7位上再引入酯键后3个化合物活性比先导化合物强。     

Substitution at the 8-position of 3'-deoxy-cyclic ADP-carbocyclic-ribose, a highly potent Ca2+-mobilizing agent, provides partial agonists

We previously showed that 3'-deoxy-cyclic ADP-carbocyclic-ribose (3'-deoxy-cADPcR, 4) is a stable and highly potent analogue of cyclic ADP-ribose (cADPR, 1), a Ca(2+)-mobilizing second messenger. From these results, we designed and synthesized other 3'-modified analogues of cADPcR having a substituent at the 8-position and found that this modification at the 8-position made them partial agonists. Among these compounds, 8-NH(2)-3'-deoxy-cADPcR (10) was identified as a potent partial agonist with an EC(50) value of 17 nM.     

Syntheses and biological evaluation of topoisomerase I-targeting agents related to 11-[2-(N,N-dimethylamino)ethyl]-2,3-dimethoxy-8,9-methylenedioxy-11H-isoquino[4,3-c]cinnolin-12-one (ARC-31)

Several 11-ethyl-2,3-dimethoxy-8,9-methylenedioxy-11H-isoquino[4,3-c]cinnolin-12-ones with varied functionality on the ethyl substituent have exhibited potent topoisomerase I (TOP1) targeting activity and antitumor activity. The influence of various polar substituents at the 2-position of the 11-ethyl substituent, including N-methylamine, N-isopropylamine, hydroxyl, and hydroxylamino groups, on TOP1-targeting activity and cytotoxicity was assessed. The N-methylamine and N-isopropylamine derivatives were also evaluated as antitumor agents in athymic nude mice with MDA-MB-435 human tumor xenografts. Both compounds were active as antitumor agents upon either parenteral or oral administration.     

N-4-Pyrimidinyl-1H-indazol-4-amine inhibitors of Lck: indazoles as phenol isosteres with improved pharmacokinetics

2,4-Dianilino pyrimidines are well-known inhibitors of tyrosine kinases including lymphocyte specific kinase (Lck). Structure-activity relationships at the 4-position are discussed and rationalised. Examples bearing a 2-methyl-5-hydroxyaniline substituent at the 4-position were especially potent but showed poor oral pharmacokinetics. Replacement of this substituent by 4-amino(5-methyl-1H-indazole) yielded compounds with comparable enzyme potency and improved pharmacokinetic properties.     

Modulation of the 6-position of benzopyran derivatives and inhibitory effects on the insulin releasing process

The synthesis of different series of 4- and 6-substituted R/S-3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans is described. All of these new benzopyran derivatives were bearing, at the 4-position, a phenylthiourea moiety substituted on the phenyl ring by a meta or a para-electron-withdrawing group such as Cl or CN. The study aimed at exploring the influence of the nature of the substituent at the 6-position in order to develop new benzopyran-type K(ATP) channel activators exhibiting an improved selectivity towards the insulin secreting cells. The original compounds were examined in vitro on rat pancreatic islets (inhibition of insulin release) as well as on rat aorta rings (vasorelaxant effect) and their activity was compared to that of the reference K(ATP) channel activators (±)-cromakalim, (±)-pinacidil, diazoxide and to previously synthesized cromakalim analogues. Structure-activity relationships indicated that the inhibitory effect on the insulin secreting cells was related to the lipophilicity of the molecules and to the size of the substituent located at the 6-position. A marked inhibitory activity on the insulin secretory process was obtained with molecules bearing a bulky tert-butyloxycarbonylamino group at the 6-position (20-23). The latter compounds were found to have the same efficacy on the pancreatic endocrine tissue than some previously described molecules. Lastly, radioisotopic experiments further identified R/S-N-4-chlorophenyl-N'-(6-tert-butyloxycarbonylamino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-4-yl)thiourea (23) as a K(ATP) channel opener.     

Development of novel lithocholic acid derivatives as vitamin D receptor agonists

Lithocholic acid (2) was identified as the second endogenous ligand of vitamin D receptor (VDR), though its binding affinity to VDR and its vitamin D activity are very weak compared to those of the active metabolite of vitamin D₃, 1α,25-dihydroxyvitamin D₃ (1). 3-Acylated lithocholic acids were reported to be slightly more potent than lithocholic acid (2) as VDR agonists. Here, aiming to develop more potent lithocholic acid derivatives, we synthesized several derivatives bearing a 3-sulfonate/carbonate or 3-amino/amide substituent, and examined their differentiation-inducing activity toward human promyelocytic leukemia HL-60 cells. Introduction of a nitrogen atom at the 3-position of lithocholic acid (2) decreased the activity, but compound 6 bearing a 3-methylsulfonate group showed more potent activity than lithocholic acid (2) or its acylated derivatives. The binding of 6 to VDR was confirmed by competitive binding assay and X-ray crystallographic analysis of the complex of VDR ligand-binding domain (LBD) with 6.     

6-Carboxy-5,7-diarylcyclopenteno[1,2-b]pyridine derivatives: a novel class of endothelin receptor antagonists

Compounds (2-5) with a 6-carboxy-5,7-diarylcyclopentenopyridine skeleton were designed, synthesized, and identified as a new class of potent non-peptide endothelin receptor antagonists. The regio-isomer 2 was found to show potent inhibitory activity with an IC(50) value of 2.4 nM against (125)I-labeled ET-1 binding to human ET(A) receptors and a 170-fold selectivity for ET(A) over ET(B) receptors. Furthermore, 2 displayed more potent in vivo activity than did the indan-type compound 1 in a mouse ET-1 induced lethality model, suggesting the potential of 2 as a new lead structure. Derivatization on substituted phenyl groups at the 5- and 7-positions of 2 revealed that a 3,4-methylenedioxyphenyl group at the 5-position and a 4-methoxyphenyl group at the 7-position were optimal for binding affinity. Further derivatization of 2 by incorporating a substituent into the 2-position of the 4-methoxyphenyl group led to the identification of a more potent ET(A) selective antagonist 2p with an IC(50) value of 0.87 nM for ET(A) receptors and a 470-fold selectivity. In addition, 2p showed highly potent in vivo efficacy (AD(50): 0.04 mg/kg) in the lethality model.     

Synthesis and structure-activity relationships of 2-amino-8-hydroxyadenines as orally active interferon inducing agents

Recently, we have reported the 8-hydroxyadenine derivatives (2–4) as a novel class of interferon (IFN) inducing agents. In the present study, a series of 8-hydroxyadenines, which possess various amino moieties at the adenine C(2)-position, were synthesized and evaluated for their ability to induce endogenous IFN in comparison to the known active agent, Imiquimod. Among the compounds prepared, compound 9o possessing a 2-methoxyethylamino group at C(2)-position of adenine was found to exhibit potent IFN inducing activity in vivo. Compound 9o induced IFN from the dosage of 0.1 mg/kg, which was 30-fold potent than that of Imiquimod, and showed a good oral bioavailability (F=81%).     

Structure-requirements of isocoumarins, phthalides, and stilbenes from Hydrangeae Dulcis Folium for inhibitory activity on histamine release from rat peritoneal mast cells.

We examined the structure-activity relationships of isocoumarins, phthalides and stilbenes isolated from Hydrangeae Dulcis Folium and related compounds for the inhibition of histamine release in rat peritoneal mast cells. The activities of isocoumarins such as thunberginols A and B were more potent than those of dihydroisocoumarins such as hydrangenol and thunberginol G. The double bond at the 3-position seemed to be essential to potentiate the activity. The hydroxyl groups at the 8-, 3'- and 4'-positions of isocoumarin were essential for the activity, while the hydroxyl group at the 6-position was scarcely needed. Since the activities of benzylidenephthalides such as thunberginol F were more potent than those of hydramacrophyllols A and B, the presence of a double bond at the 3-position was needed to increase the activity. Moreover, the hydroxyl group at the 8-position was essential for the activity. On the time course study, thunberginols A, B and F completely inhibited histamine release by pretreatment at 100 microM for 1 to 15 min, whereas DSCG inhibited histamine release only following 1-min pretreatment at 1000 microM. These results suggested that the mechanisms of the inhibitory effect of thunberginols are different from that of DSCG.     

Synthesis and biological evaluation of 4'-(6,7-disubstituted-2,4-dihydro-indeno[1,2-c]pyrazol-3-yl)-biphenyl-4-ol as potent Chk1 inhibitors

A new series of potent tricyclic pyrazole-based Chk1 inhibitors are described. Analogues disubstituted on the 6- and 7-positions show improved Chk1 inhibition potency compared with analogues with a single substituent on either the 6- or 7-position. Based on the lead compound 4'-(6,7-dimethoxy-2,4-dihydro-indeno[1,2-c]pyrazol-3-yl)-biphenyl-4-ol (2), detailed SAR studies on the 6- and 7-positions were performed. 3'-morpholin-4'-yl-propoxy, pyridin-4'-ylmethoxy, pyridin-3'-ylmethoxy, 2'-(5'-ethyl-pyridin-2'-yl)-ethoxy, pyridin-2'-ylethoxy, (6'-methyl-pyridin-2'-yl)-propoxyethoxy, 2',3'-dihydroxyl-1'-yl-propoxy, and tetrahydro-furan-3'-yloxy have been identified as the best groups on the 6-position when the 7-position is substituted with methoxyl group. Pyridin-2'-ylmethoxy and pyridin-3'-ylmethoxy have been identified as the best substituents at the 7-position while the 6-position bearing methoxyl group. These compounds significantly potentiate the cytotoxicity of DNA-damaging antitumor agents in a cell-based assay and efficiently abrogate the doxorubicin-induced G2/M and the camptothecin-induced S checkpoints, suggesting that their potent biological activities are mechanism-based through Chk1 inhibition.     

Himbacine derived thrombin receptor (PAR-1) antagonists: SAR of the pyridine ring

The structure-activity relationship (SAR) of the vinyl pyridine region of himbacine derived thrombin receptor (PAR-1) antagonists is described. A 2-vinylpyridyl ring substituted with an aryl or a heteroaryl group at the 5-position showed the best overall PAR-1 affinity and pharmacokinetic properties. One of the newly discovered analogs bearing a 5-(3-pyridyl) substituent showed excellent PAR-1 affinity (Ki = 22 nM) and oral activity with reduced ClogP and improved off-target selectivity compared to an earlier development candidate.     

Design, efficient synthesis, and anti-HIV activity of 4'-C-cyano- and 4'-C-ethynyl-2'-deoxy purine nucleosides

Some 4'-C-ethynyl-2'-deoxy purine nucleosides showed the most potent anti-HIV activity among the series of 4'-C-substituted 2'-deoxynucleosides whose 4'-C-substituents were methyl, ethyl, ethynyl and so on. Our hypothesis is that the smaller the substituent at the C-4' position they have, the more acceptable biological activity they show. Thus, 4'-C-cyano-2'-deoxy purine nucleosides, whose substituent is smaller than the ethynyl group, will have more potent antiviral activity. To prove our hypothesis, we planned to develop an efficient synthesis of 4'-C-cyano-2'-deoxy purine nucleosides (4'-CNdNs) and 4'-C-ethynyl-2'-deoxy purine nucleosides (4'-EdNs). Consequently, we succeeded in developing an efficient synthesis of six 2'-deoxy purine nucleosides bearing either a cyano or an ethynyl group at the C-4' position of the sugar moiety from 2'-deoxyadenosine and 2,6-diaminopurine 2'-deoxyriboside. Unfortunately, 4'-C-cyano derivatives showed lower activity against HIV-1, and two 4'-C-ethynyl derivatives suggested high toxicity in vivo.     

Structure--activity relationships of 1beta-methyl-2-(5-phenylpyrrolidin-3-ylthio)carbapenems

Structure--activity relationship studies of 1beta-methyl-2-[(3S,5R)-5-(4-aminomethylphenyl)pyrrolidin-3-ylthio]carbapenems, especially those pertaining to the relationship between antibacterial activity and side-chain structure were conducted. These studies suggested that the trans-(3S,5R)-5-phenylpyrrolidin-3-ylthio side-chain and the aminomethyl group at the 4-position of the phenyl ring play a key role in enhancing the antibacterial activity against the MRSA and Pseudomonas aeruginosa strains. In particular, the basicity of a substituent at the 4-position of the phenyl ring were shown to greatly contribute to the antibacterial activity against MRSA and methicillin-resistant Staphyloccocus epidermidis strains. In contrast, the amidine group was shown to lead to potent antibacterial activity against P. aeruginosa strains comparable to that of imipenem, however, a good correlation between the basicity of the 4-substituent and antipseudomonal activity was not observed. In conclusion, the 4-aminomethyl or methylaminomethyl group on the phenyl ring was the best substituent for antipseudomonal activity.