Discovery, Synthetic Methodology, and Biological Evaluation for Antiphotoaging Activity of Bicyclic[1,2,3]triazoles: In Vitro and in Vivo Studies

Ring-Opening Coupling of Cyclopropanol with 1,2,3-Triazole for the Synthesis of Fused Triazoles

A radical ring-opening arylation of cyclopropanol with 1,2,3-triazole has been achieved. This synthetic protocol provides straightforward access to a wide range of structurally diverse and chiral 4,5,6,7-tetrahydro[1,2,3]triazolo[1,5-a]pyridines with high efficiency from readily available chiral cyclopropanols.

Discovery of matrix metalloproteinase inhibitors as anti-skin photoaging agents

Photodamage is the result of prolonged exposure of the skin to sunlight. This exposure causes an overexpression of matrix metalloproteinases (MMPs), leading to the abnormal degradation of collagen in the skin tissue and resulting in skin aging and damage. This review presents a detailed overview of MMPs as a potential target for addressing skin aging. Specifically, we elucidated the precise mechanisms by which MMP inhibitors exert their anti-photoaging effects. Furthermore, we comprehensively analyzed the current research progress on MMP inhibitors that demonstrate significant inhibitory activity against MMPs and anti-skin photoaging effects. The review also provides insights into the structure-activity relationships of these inhibitors. Our objective in conducting this review is to provide valuable practical information to researchers engaged in investigations on anti-skin photoaging.

Advances in the Synthesis of Fused 1,2,3-Triazoles via a MCR-Intramolecular Azide-Alkyne Cycloaddition Approach

The present review narrates several reports which deal with the synthesis of fused 1,2,3-triazole containing scaffolds following a sequential multicomponent reaction (MCR)-intramolecular azide-alkyne cycloaddition (IAAC) approach. The reviewed reactions were cleverly designed so as to incorporate azide and alkyne functionalities in the MCR product which was then subjected to IAAC. The review is divided into two sections based on the number of components in the multicomponent reaction. We have aimed at a critical discussion and also have highlighted either advantages or disadvantages of each methodology.

Laser-assisted nanoparticle delivery to promote skin absorption and penetration depth of retinoic acid with the aim for treating photoaging

Retinoic acid (RA) is an approved treatment for skin photoaging induced by ultraviolet (UVA). Topically applied RA is mainly located in the stratum corneum (SC) with limited diffusion into the deeper strata. A delivery system capable of facilitating dermal delivery and cellular internalization for RA is critical for a successful photoaging therapy. Two delivery approaches, namely nanoparticles and laser ablation, were combined to improve RA's absorption efficacy and safety. The nanoparticle absorption enhancement by the lasers was compared between full-ablative (Er:YAG) and fractional (CO₂) modalities. We fabricated poly-L-lactic acid (PLA) and PLA/poly(lactic-co-glycolic acid) (PLGA) nanoparticles by an emulsion-solvent evaporation technique. The mean size of PLA and PLA/PLGA nanocarriers was 237 and 222 nm, respectively. The RA encapsulation percentage in both nanosystems was > 96 %. PLA and PLA/PLGA nanocarriers promoted RA skin deposition by 5- and 3-fold compared to free control. The ablative lasers further enhanced the skin deposition of RA-loaded nanoparticles, with the full-ablative laser showing greater permeation enhancement than the fractional mode. The skin biodistribution assay evaluated by confocal and fluorescence microscopies demonstrated that the laser-assisted nanoparticle delivery achieved a significant dermis and follicular accumulation. The cell-based study indicated a facile uptake of the nanoparticles into the human dermal fibroblasts. The nanoparticulate RA increased type I collagen and elastin production in the UVA-treated fibroblasts. A reduction of matrix metalloproteinase (MMP)-1 was also highlighted in the photoaging cells. The calculation of therapeutic index (TI) by multiplying collagen/elastin elevation percentage and skin deposition predicted better anti-photoaging performance in Er:YAG laser-assisted nanoparticle delivery than CO₂ laser. Nanoencapsulation of RA decreased the cytotoxicity against skin fibroblasts. In vivo skin tolerance test on a nude mouse showed less skin damage after topical application of the nanoparticles than free RA. Our results hypothesized that the laser-mediated nanoparticle delivery provided an efficient and safe use for treating photoaging.

1,6-Addition of 1,2,3-NH triazoles to para-quinone methides: Facile access to highly selective N1 and N2 substituted triazoles

The regioselective syntheses of N¹ and N² substituted triazoles through a 1,6-addition reaction of 1,2,3-NH triazoles to p-quinone methide were achieved under mild reaction conditions. The present reactions showed superior results in terms of selectivity, mild reaction conditions, short reaction time and broad substrate scope with good functional-group compatibility. Considering the high synthetic value of N¹- and N²-substituted compounds and p-QM related research, the present strategy will greatly benefit researchers in various fields.

Addition of benzyl ethers to alkynes: a metal-free synthesis of 1H-isochromenes

Bromotrimethylsilane (TMSBr)-promoted intramolecular cyclization of (o-arylethynyl)benzyl ethers to form 1H-isochromenes at room temperature is reported. Further studies indicated that vinyl carbocations are the reaction intermediates which are stabilized by the conjugated aryl groups. Thus, O-addition of benzyl ethers/tetrahydropyrans to alkynes was achieved under metal-free, acidic conditions. These reaction conditions were compatible with an alkynyl Prins reaction; therefore, 1H-isochromenes were produced directly from alkynyl benzaldehydes and alkynyl alcohols using a one-pot procedure.

Association Between Micronutrient Concentrations and Human Epididymis Protein 4

Background

Human epididymis protein 4 (HE4) has been frequently used to study in many malignant tumors, while serum nutritional markers are used to determine a person's health status. However, the link between serum micronutrient concentrations and HE4 has not yet been clarified.

Methods

A total of 2464 eligible female participants and serum concentrations of nutritional biomarkers were chosen from the National Health and Nutrition Examination Surveys (NHANES) 2001-2002. For statistical analysis, we used the χ ² test, multivariable linear regression, and analysis of variance. Adjusted models were used, and the concentrations of serum nutritional biomarkers were divided into quartiles.

Results

The mean age of the participants was 48.07 years. Among twelve micronutrients, five were negatively associated with HE4 in models 1, 2 and 3. Only α-carotene, trans-β-carotene, cis-β-carotene, trans-lycopene and retinol were associated with HE4, with beta coefficients of -0.102, -0.027, -0.506, -0.131 and -0.054, respectively. After performing quartile-based analysis, statistical significance was only found for serum α-carotene, trans-lycopene, and retinol in the three models. In model 3, the beta coefficients [95% confidence intervals (CIs)] of the fourth quartiles compared to the first quartiles for α-carotene, trans-lycopene, and retinol were -3.390 (-5.053, -1.727), -4.036 (-5.722, -2.351) and -4.146 (-5.899, -2.393), respectively. Serum concentrations of these three nutritional biomarkers were inversely related to serum HE4 concentration (p trend <0.001).

Conclusion

HE4 is a useful and novel biomarker that can be used with many diseases, especially ovarian cancer. Three of our selected micronutrients were inversely associated with HE4 concentration. Supplement of micronutrients may reduce the levels of HE4 and the subsequent of ovarian cancer's risk. Therefore, a formula that correlates HE4 with nutritional biomarkers needs to be established before use in clinical applications.

Access to (Z)-β-Substituted Enamides from N1-H-1,2,3-Triazoles

A direct ring-opening/nucleophilic substitution reaction of N1-H-1,2,3-triazoles has been described. Divergent (Z)-β-halogen- or sulfonyl-substituted enamides could be stereospecifically synthesized in a tunable manner. This strategy might not only enable a new ring-opening method of N1-H-1,2,3-triazoles under nonmetal catalysis and mild reaction conditions but also offer a good opportunity to reliably access versatile (Z)-β-substituted enamides that could be used as synthetic precursors for further synthetic transformations.

Bach2 regulates autophagy to modulate UVA-induced photoaging in skin fibroblasts

Senescence is a cellular process that can be initiated by certain stressors such as UVA irradiation. The mechanism by which skin cells protect themselves from the UVA-induced senescence has not been fully investigated. Here, we demonstrate that Bach2 modulates the extent of UVA-induced photoaging through regulation of autophagy in skin fibroblasts. In fact chronic exposure of skin fibroblasts to UVA resulted in a significant decrease in Bach2 expression, both in vitro and in vivo. In addition, knockdown of Bach2 in skin fibroblasts led to an increased expression of cell senescence-related genes, which further enhanced the UVA irradiation-induced photoaging. On the other hand, the overexpression of Bach2 resulted in a decrease in the expression of cell senescence-related genes. We also demonstrate that the knockdown of Bach2 in skin fibroblasts can lead to a decreased expression of autophagy-related genes and vice versa, suggesting that autophagy is involved in Bach2-mediated regulation of senescence in skin fibroblasts. Additionally, inhibition of autophagy with autophagy inhibitor 3-MA suppressed the expression of autophagy-related proteins and promoted cell senescence. Furthermore, knockout of Atg5 or Atg7 in embryonic mouse fibroblasts led to a significant increase in the expression of cell senescence-related genes. Immunoprecipitation assays further demonstrated that Bach2 directly interacts with Beclin-1, Atg3, Atg7, and LC3 in fibroblasts. Taken together, these findings revealed a critical role for Bach2 in suppressing the UVA irradiation-induced cell senescence via autophagy in skin fibroblasts. Bach2 can therefore be a potential target for the therapy of UV-induced photoaging because of its ability to regulate the process of autophagy in the skin.

Studies to explore the UVA photosensitizing action of 9-phenylacridine in cells by interaction with DNA

Acridine and its derivatives are well known for their DNA binding properties. In this report, we present our findings on evaluating different binding parameters of the interaction of 9-phenylacridine (ACPH) with DNA. Absorption spectroscopic studies including standard and reverse titration, the effects of ionic strength and temperature on titration, and Job plot analysis were done to calculate the binding constant and determine the different thermodynamic parameters and stoichiometry of the binding. Spectrofluorimetry and circular dichroism (CD) spectral titration were also utilized to confirm these findings. The results indicated that ACPH binds to DNA reversibly through non-electrostatic interactions by hydrogen bonding and van der Waals interactions. The binding constant and the number of binding sites were of the order 10³ M^-1 and ≈2, respectively with a binding stoichiometry of 1:4. The binding of ACPH with DNA was spontaneous, exothermic and enthalpy-driven. The extent of uptake of ACPH in B16 melanoma cells was estimated. As this compound absorbs in the UVA region, the effect of treatment with ACPH prior to UVA exposure was assessed to evaluate its phototoxicity in these cells. Our results indicated that the binding to DNA enhanced damage to sensitize cells to killing through apoptosis. Our findings indicated its potential to act as a photosensitizer.

DUOX2 participates in skin aging induced by UVB in HSF2 cells by activating NF-κB signaling

Skin and in particular photoaging or premature aging, are caused by a variety of factors, including hormone imbalance and exposure to ultraviolet radiation. The aim of the present study was to explore the roles of Dual oxidase 2 (DUOX2) and related NF-κB signals in skin photoaging. Cell models of photoaging were constructed by irradiating human skin fibroblast lines (HSF2) with ultraviolet B (UVB) of different doses (0, 15, 30 and 60 mj/cm²). The cell counting kit-8 (CCK8) was used to determine cell proliferation. Flow cytometry was used to determine the production of reactive oxygen species (ROS). A biochemical method was to determine the content of hydrogen peroxide, and the quantitative PCR (qPCR) was used to determine the expression of matrix metalloproteinase 2 (MMP2), matrix metalloproteinase 9 (MMP9), Col-Ⅰ and α-SMA in the cells. Enzyme-linked immunosorbent assay (ELISA) was used to determine the expression of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Western blot analysis was performed to determine the expression of DUOX2, p65 and p-p65. The results showed that,UVB irradiation dose- and time-dependently inhibited the proliferation of HSF2 cells. Cellular inflammatory response, ROS production and hydrogen peroxide increase was promoted. Col-Ⅰ and α-SMA were downregulated, MMP2 and MMP9 were upregulated, and the phosphorylation of NF-κB p65 was promoted. The above indicators were all reversed by interference with DUOX2. Overexpression of DUOX2 has an effect that is similar to UVB irradiation, but the effects can be significantly weakened by NF-κB inhibitor, NAC. Upregulation of DUOX2 expression plays a crucial role in UVB-induced aging of HSF2 cells. The specific mechanism is related to the promotion of ROS production and cellular inflammatory response and activation of NF-κB signals.

9-phenyl acridine photosensitizes A375 cells to UVA radiation

Acridines are an important class of bioactive molecules having varied uses. Its derivative, 9-phenylacridine (ACPH) had been found to exhibit antitumor activity both in cell lines and in vivo model. Its DNA binding ability and absorbance in the ultraviolet range encouraged us to investigate its role as a photosensitizer with UVA radiation. We investigated the effects of ACPH prior to UVA exposure on in vitro DNA through photo-cleavage assay. Effect of such treatment was also studied in cultured A375 melanoma cells. Endpoints studied included morphological changes, evaluation of cellular viability, scratch assay, intracellular reactive oxygen species (ROS) production, DNA damage, lipid peroxidation, glutathione (GSH) level, autophagy, cell cycle progression, depletion of mitochondrial membrane potential (ΔΨmt), induction of apoptosis and Hoechst dye efflux assay. Our findings indicated that ACPH could sensitize damage to DNA induced by UVA both in vitro and in cells. It could also potentiate cell killing by UVA. It arrested cells in G2/M phase and induced apoptotic death through mitochondria mediated pathway. This sensitization was through enhancement of intracellular ROS. Our findings also indicated that the stem cells side population was reduced on such treatment. The findings are important as it indicates ACPH as a promising photosensitizer and indicates its possible role in photodynamic therapy.

An Efficient Approach to Phosphorylated Isoindoline Fused with Triazoles via Zn-Catalyzed Cascade Cyclization of 2-Propynol Benzyl Azides and Diarylphosphine Oxides

An efficient approach for the synthesis of phosphorylated isoindoline fused with triazoles via Zn(OTf)₂-catalyzed cascade cyclization of easily prepared ortho-propynol benzyl azides and diarylphosphine oxides is developed. The transformation occurred smoothly in moderate to excellent yields and tolerated various propargylic alcohol substrates.

Iron-Catalysed Remote C(sp3 )-H Azidation of O-Acyl Oximes and N-Acyloxy Imidates Enabled by 1,5-Hydrogen Atom Transfer of Iminyl and Imidate Radicals: Synthesis of γ-Azido Ketones and β-Azido Alcohols

In the presence of a catalytic amount of iron(III) acetylacetonate [Fe(acac)₃ ], the reaction of structurally diverse ketoxime esters with trimethylsilyl azide (TMSN₃ ) afforded γ-azido ketones in good to excellent yields. This unprecedented distal γ-C(sp³ )-H bond azidation reaction went through a sequence of reductive generation of an iminyl radical, 1,5-hydrogen atom transfer (1,5-HAT) and iron-mediated redox azido transfer to the translocated carbon radical. TMSN₃ served not only as a nitrogen source to functionalise the unactivated C(sp³ )-H bond, but also as a reductant to generate the catalytically active Fe^II species in situ. Based on the same principle, a novel β-C(sp³ )-H functionalisation of alcohols via N-acyloxy imidates was subsequently realised, leading, after hydrolysis of the resulting ester, to β-azido alcohols, which are important building blocks in organic and medicinal chemistry.

Synthesis of Fused Bicyclic [1,2,3]-Triazoles from γ-Amino Diazoketones

Triazoles are an important class of N-heterocycles that are well known for their broad biological activities. In this work, we would like to demonstrate a direct synthesis of the rare fused bicyclic [1,2,3]-triazoles, employing γ-N-protected amino diazoketones as useful synthetic platforms. The strategy was based on the deprotection of a trifluoroacetamide group for the intramolecular and in situ generation of an α-diazo imine intermediate, followed by a 5-endo-dig cyclization to construct the bicyclic unit. In this fashion, the synthesis of a series of fused bicyclic [1,2,3]-triazoles could be carried out in good to excellent yields (63-95%).

Overexpression of klotho in adipose-derived stem cells protects against UVB-induced photoaging in co-cultured human fibroblasts

Co-culture methods are widely used in tissue engineering to drive tissue formation with the direct or indirect interaction of multiple cell types. Klotho is a novel biomarker involved in aging. In this study, we evaluated the protective effects of klotho overexpressed adipose-derived stem cells (ADSCs) against ultraviolet radiation B (UVB)-induced photoaging in co-cultured human skin fibroblasts (HSF2 cell line). Furthermore, the involvement of P38 mitogen-activated protein kinase (MAPK) signaling was investigated. ADSCs were isolated from human subcutaneous adipose tissue and the 3rd generation of ADSCs was used after being identified. Klotho overexpression (OE) lentivirus vectors were constructed and identified in ADSCs. The HSF2 cells were seeded in the upper layer of the Transwell co-culture plate (0.4 µm pore polycarbonate membrane) and ADSCs were seeded in the lower layer. UVB irradiation of HSF2 cells was performed using UVB lamps in uncovered petri dishes at room temperature. The present results indicated that the proliferation of ADSCs was increased by klotho OE. Furthermore the proliferation and collagen content of HSF2 were decreased by UVB irradiation in a dose-dependent manner. By contrast, the protein level of matrix metalloproteinases (MMP) 1, 3 and p-P38 in HSF2 were upregulated. In the co-culture system, relative mRNA expression of MMP-1 and MMP-3 as well as protein level of MMP-1, MMP-3 and p-P38 in HSF2 were reduced by co-culture with klotho overexpressed ADSCs when exposed to UVB (20 mJ/cm2). By contrast, the collagen content of HSF2 was increased. Collectively, OE of klotho in ADSCs notably ameliorates UVB-induced photoaging in co-cultured HSF2, and these effects were potentially achieved by increasing the collagen content and decreasing the protein level of MMP-1, MMP-3 and p-P38.

Practical, high-yield synthesis of thiol-terminated diacetylenes for formation of conductive monolayers

Self-assembled monolayers of thiol terminated conjugated diacetylenes can be cross-linked using ultraviolet light to form highly conjugated polydiacetylenic conductive monolayers¹; however, the reported syntheses of the diacetylene monomers present numerous problems that prevent the wide spread application of these in functional materials. We report a redesigned four-step synthesis that proceeds in 75-80 % overall yields and allows gram scale production of an array of thiol terminated conjugated diacetylenes, thereby allowing examination and application of these low-dimensional conductive materials.

An efficient synthesis of 4,5-disubstituted-2H-1,2,3-triazoles from nitroallylic derivatives via a cycloaddition–denitration process

A variety of nitroallylic derivatives were smoothly reacted with sodium azide in the presence of p-TsOH to form synthetically-viable triazoles.

Copper-Catalyzed Cross-Dehydrogenative N2-Coupling of NH-1,2,3-Triazoles with N,N -Dialkylamides: N-Amidoalkylation of NH-1,2,3-Triazoles

An efficient copper-catalyzed C-N bond formation by N-H/C-H cross-dehydrogenative coupling (CDC) between NH-1,2,3-triazoles and N,N-dialkylamides has been developed. The method provided N-amidoalkylated 1,2,3-triazoles with moderate to high yields, and the reactions showed high N²-selectivities when 4,5-disubstituted NH-1,2,3-triazoles served as the substrates.

The characterization of 1-(4-bromophenyl)-5-phenyl-1H-1,2,3-triazole on acute toxicity, antimicrobial activities, photophysical property, and binding to two globular proteins

1-(4-Bromophenyl)-5-phenyl-1H-1,2,3-triazole (BPT) was a newly synthesized compound. The acute toxicities of BPT to mice by intragastric administration have been determined and the result indicates that the intragastric administration of BPT did not produce any significant toxic effect on Kunming strain mice. It is also evaluated for the antimicrobial activity of BPT against three kinds of plant mycoplasma, Fusarium Wilt (race 4), Colletotrichum gloeosporioides Penz. and Xanthomonas oryzae by different method in vitro. The compound exhibited distinct inhibitory activities against Fusarium Wilt (race 4) and Colletotrichum gloeosporioides Penz. by mycelium growth rate test and the values of EC₅₀ were 29.34 and 12.53μg/mL respectively. And BPT had also the most potent inhibitory activities against Xanthomonas oryzae when compared with that of control drugs by the agar well diffusion method. In addition, the structural and photophysical properties of BPT including ionization energy, electron affinities, and theoretical spectrum was studied by quantum-chemical methods. Then the interaction of BPT with two kinds of globular proteins, human immunoglobulin (HIg) and bovine hemoglobin (BHg) was investigated by using UV-vis absorption spectra, synchronous fluorescence, 3D fluorescence spectra, and fluorescence titration in combination with molecular modeling. UV-vis absorption, 3D and synchronous fluorescence measurements show that BPT has influence on the microenvironment surrounding HIg or BHg in aqueous solution and the fluorescence experiments show that BPT quenches the fluorescence intensity of HIg or BHg through a static mechanism. The binding parameters including the binding constants, the number of binding site and average binding distance between BPT and HIg or BHg at different temperatures were calculated. The thermodynamic parameters suggest that the hydrophobic interaction is the predominant intermolecular forces in stabilizing the BPT-HIg or BPT-BHg complex. Molecular docking was performed to reveal that the BPT moiety binds to the hydrophobic cavity of HIg or BHg and they are in good agreement with the spectroscopic measurements.

Protective effect of gelatin peptides from pacific cod skin against photoaging by inhibiting the expression of MMPs via MAPK signaling pathway

Chronic exposure to ultraviolet (UV) irradiation causes skin photoaging. This study was undertaken to identify the anti-photoaging mechanisms of gelatin hydrolysate (CH) derived from pacific cod skin. Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) and ELISA assays were used to investigate the effects of CH on matrix metalloproteinases (MMPs) and the signaling pathways after UV irradiation by using a mice skin photoaging model. The average molecular weight of CH was 1200Da, and 273/1000 residues were hydrophobic, Gly-Pro and Gly-Leu sequences and Arg at C-terminus appeared frequently in CH. CH improved pathological changes of collagen fibers and significantly inhibited collagen content reduction in photoaging skin. Moreover, CH blocked the up-regulated expression of interstitial collagenase (MMP-1), stromelysin 1 (MMP-3), and gelatinase (MMP-9) in photoaging skin. Besides, CH suppressed the activities of MMPs by increasing the contents of tissue inhibitors of matrix metalloproteinases (TIMPs). CH significantly reduced the UV irradiation-dependent up-regulated phosphorylation of ERK and p38 in the mitogen-activated protein kinase (MAPK) signaling pathway. Furthermore, it inhibited the activation of activator protein 1 (AP-1) by down-regulating the mRNA level of c-Jun and c-Fos, which are the two transcription factors responsible for the regulation of MMPs expression. CH can effectively protect against UV irradiation-induced skin photoaging by inhibiting the expression and the activity of MMPs.

Catechol-based matrix metalloproteinase inhibitors with additional antioxidative activity

New catechol-containing chemical entities have been investigated as matrix metalloproteinase inhibitors as well as antioxidant molecules. The combination of the two properties could represent a useful feature due to the potential application in all the pathological processes characterized by increased proteolytic activity and radical oxygen species (ROS) production, such as inflammation and photoaging. A series of catechol-based molecules were synthesized and tested for both proteolytic and oxidative inhibitory activity, and the detailed binding mode was assessed by crystal structure determination of the complex between a catechol derivative and the matrix metalloproteinase-8. Surprisingly, X-ray structure reveals that the catechol oxygens do not coordinates the zinc atom.

A one-pot, three-step process for the diastereoselective synthesis of aminobicyclo[4.3.0]nonanes using consecutive palladium(ii)- and ruthenium(ii)-catalysis

A one-pot multi-step process that uses both Pd(ii)- and Ru(ii)-catalysis has been developed for the diastereoselective synthesis of aminobicyclo[4.3.0]nonanes.

Design, synthesis and antimetastatic evaluation of 1-benzothiazolylphenylbenzotriazoles for photodynamic therapy in oral cancer cells

We have designed and synthesized a new series of 1-benzothiazolylphenylbenzotriazoles 9a–p and studied their antimetastatic mechanism involved in photosensitive effects induced by UVA in oral cancer cell Ca9-22.

Cu(i)-catalyzed multicomponent cascade reactions of terminal alkynes, unactivated primary alkyl bromides, CO2 and NaN3

We have developed a mild, robust, and multicomponent cascade reaction for the synthesis of triazolo-fused dihydrooxazinones from terminal alkynes, unactivated primary alkyl bromides, carbon dioxide and sodium azide.

Structure-activity relationship study of anticancer thymidine-quinoxaline conjugates under the low radiance of long wavelength ultraviolet light for photodynamic therapy

Thymidine quinoxaline conjugate (dT-QX) is a thymidine analog with selective cytotoxicity against different cancer cells. In this study, the structure activity relationship study of dT-QX analogs was carried out under the low radiance of black fluorescent (UVA-1) light. Significantly enhanced cytotoxicity was observed under UVA-1 activation among analogs containing both thymidine and quinoxaline moieties with different length of the linker, stereochemical configuration and halogenated substituents. Among these analogs, the thymidine dichloroquinoxaline conjugate exhibited potent activity under UVA-1 activation as the best candidate with EC50 at 0.67 μM and 1.3 μM against liver and pancreatic cancer cells, respectively. In contrast, the replacement of thymidine moiety with a galactosyl residue or the replacement of quinoxaline moiety with a fluorescent pyrenyl residue or a simplified diketone structure resulted in the full loss of activity. Furthermore, it was revealed that the low radiance of UVA-1 at 3 mW/cm(2) for 20 min was sufficient enough to induce the full cytotoxicity of thymidine dichloroquinoxaline conjugate and that the cytotoxic mechanism was achieved through a rapid and steady production of reactive oxygen species.