Development of potent dipeptide-type SARS-CoV 3CL protease inhibitors with novel P3 scaffolds: design, synthesis, biological evaluation, and docking studies.

We report the design and synthesis of a series of dipeptide-type inhibitors with novel P3 scaffolds that display potent inhibitory activity against SARS-CoV 3CLpro. A docking study involving binding between the dipeptidic lead compound 4 and 3CLpro suggested the modification of a structurally flexible P3 N-(3-methoxyphenyl)glycine with various rigid P3 moieties in 4. The modifications led to the identification of several potent derivatives, including 5c-k and 5n with the inhibitory activities (Ki or IC50) in the submicromolar to nanomolar range.

Design, synthesis, and biological evaluation of novel dipeptide-type SARS-CoV 3CL protease inhibitors: structure-activity relationship study.

This work describes the design, synthesis, and evaluation of low-molecular weight peptidic SARS-CoV 3CL protease inhibitors. The inhibitors were designed based on the potent tripeptidic Z-Val-Leu-Ala(pyrrolidone-3-yl)-2-benzothiazole (8; Ki = 4.1 nM), in which the P3 valine unit was substituted with a variety of distinct moieties.

Design and synthesis of new tripeptide-type SARS-CoV 3CL protease inhibitors containing an electrophilic arylketone moiety.

We describe here the design, synthesis and biological evaluation of a series of molecules toward the development of novel peptidomimetic inhibitors of SARS-CoV 3CL(pro). A docking study involving binding between the initial lead compound 1 and the SARS-CoV 3CL(pro) motivated the replacement of a thiazole with a benzothiazole unit as a warhead moiety at the P1' site. This modification led to the identification of more potent derivatives, including 2i, 2k, 2m, 2o, and 2p, with IC(50) or K(i) values in the submicromolar to nanomolar range.

Preformulation and formulation of newly synthesized QNT3-18 for development of a skin whitening agent.

New molecules having the structure of (E)-2-(4-tert-butylbenzylidene) hydrazinecarbothioamide (QNT3-18) or 4-tert-butylphenylthiourea (QNT3-20) was synthesized and presupposed to inhibit melanogenesis through the inhibition of tyrosinase, which is involved in melanin formation. Therefore, we seek to develop these new molecules as skin whitening agents in topical formulations based on preformulation studies. QNT3-18 or QNT3-20 showed a strong single endothermic peak at 159.

Structure-activity relationship of naphthaldehydethiosemicarbazones in melanogenesis inhibition.

2-(Naphthalen-1-ylmethylene)hydrazinecarbothioamide (14, IC(50)=1.1μM) was discovered as a highly potent inhibitor of melanogenesis. To define the role of hydrogens (at N1 and N3) and sulfur in 14, a series of analogs 15a-p were synthesized and evaluated for anti-melanogenic activity using melanoma B16 cells under the stimulus of α-MSH.

Structural requirement of phenylthiourea analogs for their inhibitory activity of melanogenesis and tyrosinase.

Effect of a series of 1-phenylthioureas 1a-k and 1,3-disubstituted thioureas 2a-k were evaluated against melanin formation in melanoma B16 cell line and mushroom tyrosinase. Inhibitory activity of tyrosinase of 1-phenylthioureas 1a-k is parallel to their melanogenic inhibition. Thus, the melanogenic inhibition in melanoma B16 cells of 1-phenylthioureas could be the result of inhibition of tyrosinase.

Identification of indoline-2-thione analogs as novel potent inhibitors of α-melanocyte stimulating hormone induced melanogenesis.

Based on the hits, 3,4-dihydroquinazoline-2-thione (1) and benzimidazole-2-thione (2), a series of indole-2-thione (3) and indole-2-thiol inhibitors (4) of melanogenesis were designed, synthesized and evaluated in melanoma B16 cells under the stimulant of α-melanocyte stimulating hormone (α-MSH). The indole-2-thione compounds (3a-g) exhibited an effective inhibitory activity on melanin synthesis. The Structure-Activity Relationship (SAR) studies of 2 have revealed that in potent inhibitor 3a (>100% inhibition at 30 µM, IC50=1.

Ketonethiosemicarbazones: structure-activity relationships for their melanogenesis inhibition.

A series of 2-(1-phenylalkylidene)hydrazinecarbothioamides 2, 2-(1-phenylalkyl)hydrazinecarbothioamides 3, 2-(3,4-dihydronaphthalen-1(2H)-ylidene)hydrazinecarbothioamide (4), and 2-(1-(thiophen-2-yl)ethylidene)hydrazinecarbothioamide (5) were synthesized for their melanogenesis inhibition in melanoma B16 cells. The SAR of these ketonethiosemicarbazones revealed that the benzylidene hydrogen in aldehydethiosemicarbazones 1 can be replaced by hydrophobic moiety and substitutions with alkyl group for the terminal amino hydrogen of ketonethiosemicarbazones improved the activity appreciably. In addition, the double bond in thiosemicarbazones is an important factor for the increment of hydrophobicity.

Structure--activity relationship studies of novel arylsulfonylimidazolidinones for their anticancer activity.

To define the SAR, a series of novel N-arylsulfonylimidazolidinone derivatives were evaluated for their in vitro anticancer activity against five human tumor cell lines, including A549, COLO205, KATO III, K562, SK-OV-3 and murine leukemia (P288D1) cell line. Among them, N-(2-chloroacetyl)-6-(2-oxo-4-phenylimidazolidin-1-ylsulfonyl)-3,4-dihydroquinoline-1(2H)-carboxamide (4m) and N-cyclohexyl-6-(2-oxo-4-phenylimidazolidin-1-ylsulfonyl)-3,4-dihydroquinoline-1(2H)-carboxamide (4n) exhibited comparable in vitro anticancer activity to doxorubicin against A549, KATO III and K562 cell lines and gave superior xenographic results against NCI-H23 and SW620 cancer cell lines. Regarding the structure-activity relationship, two critical points were discovered; the steric congestion at 4-position of N-arylsulfonylimidazolidinone scaffold abolishes the activity and the bulkiness or hydrophobicity of acyl groups at 3,4-dihydroquinoline of 4, especially with carbamoyl moiety, enormously enhances the activity.

Structural requirements of (E)-6-benzylidene-4a-methyl-4,4a,5,6,7,8-hexahydronaphthalen-2(3H)-one derivatives as novel melanogenesis inhibitors.

Chalcone type compound 1a ((E)-6'-benzylidene-4a'-methyl-4',4a',7',8'-tetrahydro-3'H-spiro[[1,3]dithiolane-2,2'-naphthalen]-5'(6'H)-one) was discovered as an potent inhibitor in melanogenesis. To define its structure-activity relationship, a series of analogs 1b-n, dithiolane truncated 2a-b and ring A removed 3a-e were prepared and evaluated. The electron donating substitution on the phenyl ring (ring C) rather than an electron withdrawing group and dithiolane motif of 1 are needed for the activity enhancement.

Structural characteristics of thiosemicarbazones as inhibitors of melanogenesis.

A series of thiosemicarbazones 2(e-s) have been synthesized and studied their structure-activity relationship as melanogenesis inhibitor. Among them, (Z)-2-(naphthalen-1-ylmethylene)hydrazinecarbothioamide (2q, >100% inhibition at 10 μM, IC(50)=1.1 μM, ClogP=3.

Refinement of the pharmacophore of 3,4-dihydroquinazoline-2(1H)-thiones for their anti-melanogenesis activity.

In order to define the structural requirements of quinazoline-2(1H)-thiones 1 for their inhibitory activity on melanogenesis, a novel series of 3,4-dihydroquinazoline-2(1H)-thiones (3a-h) were prepared and screened for their melanogenesis inhibition on melanoma B16 cell line under the stimulant of alpha-MSH. The anti-melanogenesis activity of 3 is mainly mediated by the hydrogen bonding ability of thioamide unit in addition to complexation ability of thione and the hydrophobic binding power of side chain substitutions at 3-position. Thus, the pharmacophore of 3,4-dihydroquinazoline-2(1H)-thiones for their anti-melanogenesis activity could be refined as 3-hydrophobic substituted quinazolinethione.

Design and synthesis of novel hydroxyalkylaminomethylchromones for their IL-5 inhibitory activity.

A series of hydroxyalkylaminomethylchromone analogs 3 were prepared and evaluated as inhibitors of interleukin-5. The most active analog 3d inhibited interleukin-5 activity with an IC₅₀ of 17.5 μM.

Novel benzo[d]imidazole-2(3H)-thiones as potent inhibitors of the alpha-melanocyte stimulating hormone induced melanogenesis in melanoma B16 cells.

In order to determine the optimum size of heterocycle of lead compound 1 (6-methyl-3-phenethyl-3,4-dihydro-1H-quinoline-2-thione; IC(50)=0.8 microM) for inhibition of melanogenesis, we have synthesized and evaluated some benzimdazole-2(3H)-thiones 5a-e. The preliminary bioassay has shown that the benzimdazole-2(3H)-thione motif of 5 is essential structural unit for their inhibitory activity.

The scope of thallium nitrate oxidative cyclization of chalcones; synthesis and evaluation of isoflavone and aurone analogs for their inhibitory activity against interleukin-5.

The oxidative cyclization of 2'-hydroxy-6'-cyclohexylmethoxychalcones 5 using thallium (III) nitrate (TTN) in alcoholic solvents produced isoflavones 2 and (or) aurones 3 depending on the electronic nature of p-substituents on ring B. Chalcones with strong electron donating substituents (OH, OCH(3)) were exclusively converted to isoflavones 2. Chalcone with weak electron donating substituents (CH(2)CH(3)) was transformed into isoflavone 2 and the aurone 3 in approximate ratio 1:1.

Structural requirement(s) of N-phenylthioureas and benzaldehyde thiosemicarbazones as inhibitors of melanogenesis in melanoma B 16 cells.

In order to define the structural requirements of phenylthiourea (PTU), a series of thiourea and thiosemicarbazone analogs were prepared and evaluated as inhibitors of melanogenesis in melanoma B16 cells. The most potent analog was 2-(4-tert-butylbenzylidene)hydrazinecarbothioamide (1u) with an IC(50) value of 2.7 microM in inhibition of melanogenesis.

Synthesis and evaluation of novel chromone analogs for their inhibitory activity against interleukin-5.

A novel series of chromone analogs were synthesized and evaluated for their inhibitory activity against interleukin-5. Among them compounds 5-Cyclohexylmethoxy-3-(4-hydroxybenzyl)-4H-chromen-4-one (6a, 98% inhibition at 30 microM, IC50<3.0 microM) and 5-Cyclohyxylmethoxy-3-(hydroxymethyl)-4H-chromen-4-one (8a, 84% inhibition at 30 microM, IC50=7.

Evaluation of 3,4-dihydroquinazoline-2(1H)-thiones as inhibitors of alpha-MSH-induced melanin production in melanoma B16 cells.

Novel 3,4-dihydroquinazoline-2(1H)-thiones (QNTs) 1 were found to be potent inhibitors of alpha-MSH-induced melanin production. The effect of QNTs to inhibit melanin formation in B16 melanoma cells was screened in the presence of alpha-MSH. In defining the mechanism of activity, the effects on tyrosinase activity, on tyrosinase synthesis and on the depigmentation of melanin were evaluated.

Inhibitory effect of novel tetrahydropyrimidine-2(1H)-thiones on melanogenesis.

The series of imidazoldine-2-thiones 2 and tetrahydropyrimidine-2-thiones 3 were discovered as inhibitor of alpha-MSH-induced melanin production in melanoma B16 cells. The primary bioassay showed that 1-(4-ethylbenzyl)-tetrahydropyrimidine-2(1H)-thione 3e (>100% inhibition at 10 microM, IC(50)=1.2 microM) and 1-(4-tert-butylbenzyl)-tetrahydropyrimidine-2(1H)-thione 3f (>100% inhibition at 10 microM, IC(50)=0.