Morpholino Group Research Articles

Multicolor Anti‐counterfeiting Strategy and Synchronous High Capacity Storage Based on Acidochromic Organic Fluorescent Materials

Comprehensive SummaryMany industries are plagued by economic losses and product failures caused by counterfeit goods. Therefore, advanced anti‐counterfeiting techniques are continuously needed. In this study, we constructed a series of acid‐base sensitive cyclic chalcone dyes A—F by modifying different electron‐donating groups. Differences in acid sensitivity of different structures are well rationalised by NMR and theoretical calculations. Aniline is difficult to protonate than fatty amines, so there is a difference in fluorescence. Hiding and anti‐counterfeiting of information is achieved by this phenomenon. Powder X and Y are the anti‐counterfeit fluorescent powder containing montmorillonite and cyclic chalcone, which have orange fluorescence and the very similar appearance. However, under the influence of acid the Powder X containing triphenylamine modified cyclic chalcone shows red shifted fluorescence and Powder Y containing morpholino and diethylamino groups modified cyclic chalcone shows blue shifted fluorescence. Therefore, the anti‐counterfeiting strategy based on cyclic chalcone is not only limited to UV‐irradiated fluorescence development, but also has more colorization and pattern variations with the aid of acid developer. Data encryption and decryption of numbers, English alphabets and Chinese characters have been realized using A—F, which have great potential for practical applications.

Abstract 4129: Preclinical assessment of GlycoConnect™ ADCs with potency-modulated derivatives of PNU-159,682

Abstract PNU-159,682 is an oxidized secondary metabolite of nemorubicin (MMDX), and substantially more potent (2100-6400-fold) than the commonly used chemotherapeutic anthracycline doxorubicin/adriamycin, but without the dose-limiting cardiotoxicity. Based on these beneficial features, PNU-159,682 is currently being clinically evaluated (phase 1) for solid tumor indications as a payload in various antibody-drug conjugates (NBE-002, SO-N102). It must be noted, however, that the HNSTD of current PNU-based ADCs in non-human primates (~1 mg/kg) may end up in a clinical dose that is sub-optimal to achieve high tumor uptake, due to putative target-mediated drug disposition in healthy tissue. We embarked on a program to develop a set of 2nd-generation PNU-159,682 analogues with attenuated potency, to enable the generation of ADCs with a potentially improved pharmacokinetic profile. Moreover, we reasoned that the adaptation of the new PNU analogues to our proprietary best-in-class ADC technology (GlycoConnect™)1, in combination with our polar spacer technology (HydraSpace™)2 might enable PNU-based ADCs with significantly expanded therapeutic index (TI). We here exhibit the chemical synthesis of a panel of PNU-analogues with attenuated potency and enhanced tolerability, based on specific tailoring of the aminosugar morpholino group. Homogeneous and stable GlycoConnect™/HydraSpace™ ADCs were subsequently generated and evaluated in vitro and in vivo to assess efficacy and tolerability. These studies demonstrate the potential of attenuated PNU derivatives for application in stable and site-specific ADCs with anticipated higher clinic dose and potentially improved therapeutic index. 1 Wijdeven et al., Enzymatic glycan remodeling-metal free click (GlycoConnect™) provides homogenous antibody-drug conjugates with improved stability and therapeutic index without sequence engineering. mAbs 2022, 14. 2 Verkade et al. A Polar Sulfamide Spacer Significantly Enhances the Manufacturability, Stability, and Therapeutic Index of Antibody-Drug Conjugates. Antibodies 2018, 7, 12, doi:10.3390/antib7010012. Citation Format: Floris L. van Delft, Remon van Geel. Preclinical assessment of GlycoConnect™ ADCs with potency-modulated derivatives of PNU-159,682. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4129.

Abstract 2926: Structure-based design of quadruplex-binding small molecule compounds: The essential role of water molecules

Abstract The compounds CM03 and SOP1812 are tri- and tetra-substituted naphthalene diimide derivatives with high affinity for several human DNA quadruplexes. They have been designed by computer modelling based on co-crystal structures of 1st-generation substituted naphthalene diimides with human intramolecular telomeric quadruplexes. CM03 and SOP1812 have single-digit 1-20 nM anti-proliferative activity in a panel of human pancreatic ductal adenocarcinoma (PDAC) cell lines (Marchetti et al., J. Med. Chem, 2018, 61, 2500-2517: Ahmed et al., ACS Med Chem Lett, 2020, 11, 1634-1644) and significant anti-tumor activity in the MIA-PACA2 xenograft model for PDAC as well as in the more demanding KPC model. SOP1812 is bio-available at therapeutic doses and is well tolerated at these levels in animal models. It is currently being evaluated as a candidate for clinical development by Qualigen Therapeutics Inc. The role of water in protein-drug binding is well documented and known to be important for accurate estimates of drug binding energies and for docking/virtual screening studies. To date this factor has not been seriously considered in studies of ligand-quadruplex interactions even though virtual screening has emerged as an important tool for finding new chemotypes and optimizing compound libraries in silico. A high-resolution crystal structure of a naphthalene diimide quadruplex complex (PDB id 3UYH: Micco et al., J. Med. Chem., 2013, 56, 2959-2974) has now been analyzed in detail. Patterns of water molecules have been found in each of the four quadruplex grooves, associated with the cationic side chains. Only a nitrogen atom on each N-methyl-piperazine cationic end groups is in direct hydrogen bonded contact with a phosphate group. The morpholino groups each have a small and well-defined cluster of water molecules mediating between cationic nitrogen atom and phosphate group. The rest of each groove is filled by a second cluster of waters, suggesting that larger substituents can be accommodated. Data from a library of naphthalene diimide derivatives is being examined to validate the role of these waters, especially with respect to their relative mobilities and ease of displacement. Citation Format: Stephen Neidle. Structure-based design of quadruplex-binding small molecule compounds: The essential role of water molecules [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2926.

Thiosugar naphthalene diimide conjugates: G-quadruplex ligands with antiparasitic and anticancer activity

Glycosyl conjugation to drugs is a strategy being used to take advantage of glucose transporters (GLUT) overexpression in cancer cells in comparison with non-cancerous cells. Its extension to the conjugation of drugs to thiosugars tries to exploit their higher biostability when compared to O-glycosides. Here, we have synthesized a series of thiosugar naphthalene diimide conjugates as G-quadruplex ligands and have explored modifications of the amino sidechain comparing dimethyl amino and morpholino groups. Then, we studied their antiproliferative activity in colon cancer cells, and their antiparasitic activity in T. brucei and L. major parasites, together with their ability to bind quadruplexes and their cellular uptake and location. We observed higher toxicity for the sugar-NDI-NMe2 derivatives than for the sugar-NDI-morph compounds, both in mammalian cells and in parasites. Our experiments indicate that a less efficient binding to quadruplexes and a worse cellular uptake of the carb-NDI-morph derivatives could be the reasons for these differences. We found small variations in cytotoxicity between O-carb-NDIs and S-carb-NDIs, except against non-cancerous human fibroblasts MRC-5, where thiosugar-NDIs tend to be less toxic. This leads to a notable selectivity for β-thiomaltosyl-NDI-NMe212 (9.8 fold), with an IC50 of 0.3 μM against HT-29 cells. Finally, the antiparasitic activity observed for the carb-NDI-NMe2 derivatives against T. brucei was in the nanomolar range with a good selectivity index in the range of 30- to 69- fold.

Acid-Mediated Sulfonylthiolation of Arenes via Selective Activation of SS-Morpholino Dithiosulfonate.

A trifluoroacetic-acid-mediated desulfurilative sulfonylthiolation of arenes using SS-morpholino dithiosulfonate is described. This system is based on selective activation of the morpholino group over the tosyl group of the doubly transformable sulfur surrogate. Mechanistic studies suggested that the reaction proceeds through electrophilic aromatic substitution followed by sulfur extrusion. The wide substrate scope of this reaction and the transformability of the resulting thiosulfonates enable expeditious access to divergent multifunctionalized sulfides.

Synthesis, photophysical evaluation, and computational study of 2-methoxy- and 2-morpholino pyridine compounds as highly emissive fluorophores in solution and the solid state

Two 2-pyridone tautomeric analogs, methoxypyridine 4 and N-methylpyridone 5, were synthesized, and their spectroscopic properties were investigated both experimentally and computationally. A detailed photophysical study reveals that 4 shows high fluorescence quantum yields not only in chloroform but also in ethanol, and the strong fluorescence in solution might be attributed to the enol form (pyridine) of the 2-pyridone. Furthermore, we designed and synthesized novel 2-substitued pyridines to achieve more intense emissions in both solution and the solid state. Substituent modification with phenylsulfonyl, morpholino, and 4-diethylamino groups greatly affected the fluorescence properties, and methoxypyridine 7 and morpholinopyridine compound 8 showed fluorescence in various solvents (Ф = 0.59–0.95) and the solid state (Ф = 0.12–0.15). A hypsochromic shift in the emission maximum wavelength and strong fluorescence in the solid state (Ф = 0.39) were observed for dimorpholinopyridine 9. Morpholinopyridine 11 showed intense fluorescence in all nonpolar and polar solvents. Systematic time-dependent density functional theory calculations were performed for the compounds whose electronic and fluorescent maxima were computationally reproduced with good agreement to those from experiment. In detail, the drastic difference in the emission intensity between 4 and 5 in solution was successfully explained using CASSCF calculations, which revealed the presence of conical intersections between the ground and the excited states.

Synthesis and application of near-infrared absorbing morpholino-containing aza-BODIPYs

Morpholino-containing aza-BODIPYs at 3,5-positions were synthesized. The maxima absorption and emission of these dyes locate at the near-infrared region. Aza-BODIPY 1 with the morpholino group as a pH-sensitive functionality could be used to be a pH probe, and the dramatic increase in fluorescence intensity at 675 nm by about 1500 folds. Moreover, the singlet oxygen generation of PS 2 with the dibromo groups at 2,6-positions was more effective than that of the parent dye 1.

Design, synthesis and biological evaluation of novel aryl-acrylic derivatives as novel indoleamine-2,3-dioxygenase 1 (IDO1) inhibitors.

Two series of novel aryl-acrylic derivatives were designed, synthesized, and screened in enzymatic and cellular inhibitory activities. All compounds showed moderate to significant potency. The SAR analyses indicated that the semicarbazone linker is better than the 1,2,3-triazole linker. Among semicarbazone compounds that R1 bearing di-chain amino groups exhibited superior activities to those with morpholino group. Furthermore, compounds with electron-withdrawing groups at the 2-position or 4-position on the terminal phenyl ring were more active. Among these, compounds 7g, 7i, 7m and 7n exhibited the inhibitory potency in the low micromolar range and displayed negligible level of cytotoxicity against normal HeLa cells. In addition, the study suggested that the aryl-acrylic is an interesting novel scaffold for IDO1 inhibition for further development.

7-O-aminoalkyl-2,3-dehydrosilibinins: Synthesis and in vitro Anti-cancer Efficacy.

The heptaprotective flavonolignan silibinin and dehydrosilibinin have exhibited moderate antiproliferative activities toward many cancer cell lines. Considering of the nontoxic profile of these natural products, chemical modification to enhance the anticancer potentials is promising. A series of 7-O-aminoalkyl-2,3-dehydrosilibinin derivatives were synthesized and evaluated for their antiproliferative activities against several cancer cell lines. A number of the synthesized dehydrosilibinin derivatives exhibited greatly enhanced potency with 50% growth inhibition at low micromolar concentrations. Structure activity study indicated that the distance between N and 7-O on the side chain has a limited influence on the antiproliferative activity, while the presence of a morpholino group decreases the antiproliferative activities dramatically. Flow cytometry based assays on human colon cancer HCT116 cells revealed that 6a and 6c, two of the most potent derivatives, effectively arrested the cell cycle in the G2 phase and stimulated cell apoptosis. Our findings suggest that attaching an appropriate tertiary amino alkyl side chain through 7-Oalkylation on 2,3-dehydrosilibinin, would be a viable strategy for the development of silibinin derivatives as anticancer agents.

In Vitro Antitumor Activity of Alkylaminoguaiazulenes.

Guaiazulene (1,4-dimethyl-7-isopropylazulene) is present in several essential oils of medicinal and aromatic plants. There exist few studies that investigated the anticancer activity of guaiazulenes. We investigated the relative cytotoxicity of 10 alkylaminoguaiazulene derivatives towards both cancer and normal cells. Cytotoxicity towards four human oral squamous cell carcinoma (OSCC) cell lines and five types of human normal oral cells (gingival fibroblasts, periodontal ligament fibroblasts, pulp cells and keratinocytes, gingival epithelial progenitors) was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Tumor specificity (TS) was evaluated as the ratio of the mean 50% cytotoxic concentration against normal oral cells to that against OSCC cell lines. Apoptosis-inducing activity was evaluated by cleavage of poly ADP-ribose polymerase and caspsase-3 with western blot analysis. Validity of the present TS measurement method was confirmed using methotrexate. With increasing length of the alkyl group of alkylaminoguaiazulene derivatives, cytotoxicity increased. Introduction of oxygen, nitrogen or sulfur atom into the alkyl group slightly reduced cytotoxicity. Most compounds had very low TS, no synergistic action with methotrexate and doxorubicin, nor did they induce apoptosis of OSCC cells. On the other hand, compound [10], containing a morpholino group, induced apoptosis of OSCC cells. The cytotoxicity of alkylaminoguaiazulenes is not always coupled with TS and apoptosis-inducing activity.

1,3,5-Triazino Peptide Derivatives: Synthesis, Characterization, and Preliminary Antileishmanial Activity.

A library of short di-, tri-, and tetra-peptides with an s-triazine moiety at the N terminus and either an amide or ethyl ester C terminus was prepared in solution and on the solid phase. The two remaining positions of the s-triazine moiety were substituted with methoxy, morpholino, or piperidino groups. All the synthesized peptide derivatives were analyzed by HPLC and fully characterized by IR spectroscopy, 1 H and 13 C NMR spectroscopy, elemental analysis, and mass spectrometry (MALDI TOF/TOF). A preliminary study of the antileishmanial activity of the 1,3,5-triazinyl peptide derivatives revealed that four dipeptide amide derivatives showed higher antipromastigote or antiamastigote activity than the reference standard drug miltefosine with no significance acute toxicity.

Heart Failure Phenotypes Induced by Knockdown of DAPIT in Zebrafish: A New Insight into Mechanism of Dilated Cardiomyopathy

The pathogenesis of heart failure associated with dilated cardiomyopathy (DCM) may result in part from adenosine triphosphate (ATP) dysregulation in the myocardium. Under these conditions, diabetes-associated protein in insulin-sensitive tissue (DAPIT), which is encoded by the upregulated during skeletal muscle growth 5 (USMG5) gene, plays a crucial role in energy production by mitochondrial ATP synthase. To determine whether USMG5 is related to the development of heart failure, we performed clinical and experimental studies. Microarray analysis showed that the expression levels of USMG5 were positively correlated with those of natriuretic peptide precursor A in the human failed myocardium. When endogenous z-usmg5 in zebrafish was disrupted using morpholino (MO) oligonucleotides, the pericardial sac and atrial areas were larger and ventricular fractional shortening was reduced compared to in the control MO group. The expression levels of natriuretic peptides were upregulated in the z-usmg5 MO group compared to in controls. Further, microarray analysis revealed that genes in the calcium signalling pathway were downregulated in the z-usmg5 MO group. These results demonstrate that DAPIT plays a crucial role in the development of heart failure associated with DCM and thus may be a therapeutic target for heart failure.

An antibacterial composite system based on multi-responsive microgels hosting monodisperse gold nanoparticles

A multi-responsive microgel having response to pH, temperature, and salt concentration was successfully prepared using a water-soluble monomer. Microgels were readily prepared from 2-(N-morpholino)ethyl methacrylate (MEMA) via emulsion polymerization using glycidyl methacrylate as a comonomer cross-linker. The morpholino groups of MEMA residues of microgels were able to give complexation with metal containing anions such as AuCl4 − in acidic conditions. The reduction of aurate ions with sodium borohydride led to immobilized-gold nanoparticles (AuNP) in the microgel system. Average particle diameters of AuNPs were determined to be 10 ± 2 nm. The resulting AuNP-microgel system was examined as a nanoreactor for catalyst system and determined to be very effective in the reduction of 4-nitrophenol model reaction in aqueous media. AuNPs-microgel composite system had antibacterial properties against several Gram-positive and Gram-negative bacteria similar to amoxicillin. This P(MEMA-co-GMA) microgel is also very useful for different applications such as a host for metal nanoparticle production, a drug carrier or drug delivery system.

Electronic and Steric Effects of Cyclic Amino Substituents of Luciferin Analogues on a Firefly Luciferin–Luciferase Reaction

Bioluminescent and spectroscopic properties of luciferin analogues with cyclic amino substituents (1-pyrrolidinyl, piperidino, 1-azepanyl, and morpholino groups) at the 6′ position were investigated by comparing with those of 6′-dimethylaminoluciferin, to provide information on spatial and molecular environmental properties of the active site in Photinus pyralis luciferase.

Overexpression of Calr Mutants Perturbs Developmental Hematopoiesis in Zebrafish Embryos

Introduction: Calreticulin (CALR) is a 46-kDa highly conserved, multicompartmental and multifunctional protein. CALR acts as a Ca2+ binding chaperone protein and participates in ensuring proper protein and glycoprotein folding in the endoplasmic reticulum. CALR mutations have been identified in about 30% of JAK2 and MPL unmutated essential thrombocythemia and primary myelofibrosis. Although the expression of CALR mutants resulted in pathogenic thrombocytosis in adult mice, whether CALR mutants may disrupt normal hematopoiesis during early development remains unknown. Here we aimed to evaluate the effects of mutant CALR during embryonic hematopoietic development using the in vivo zebrafish model.Methods: Full-length CALR wild-type,and CALR-del52 and CALR-ins5 mutants cDNAs were subcloned in the pCS2+ vector and a bicistronic pSYC-102 T2A vector, respectively. Capped CALR mRNAs from the above vectors were micro-injected into 1-2 cells stage wild-type AB strain, Tg(cd41:GFP) and Tg(fli1:EGFP) zebrafish embryos, respectively. cd41+ thrombocytes were counted at 3 and 5 days post fertilization (dpf), respectively. Gene expression of hematopoietic lineage-specific and cytokine and cytokine receptor genes were evaluated by quantitative reverse-transcription and real-time polymerase chain reaction (Q-PCR) from 1 to 3 dpf. Morpholino (MO) was used to knock down cytokine receptor genes mpl, epor and csf3r.Results: The expression of CALR proteins from the injection of 100 pg mRNA was confirmed by CALR N-terminal and mutant specific antibodies, respectively. Expression of both CALR-del52 and CALR-ins5 mutant mRNA significantly increased the numbers of hematopoietic stem and progenitor cells in the caudal hematopoietic tissue when compared with CALR-wt mRNA at 3 dpf. No obvious changes in the angiogenesis were visualized in CALR-wt and mutant CALR expressing embryos at 3 dpf in the fli1:EGFP line when compared with uninjected control. Mutant CALR-del52 significantly increased the number of cd41+ thrombocytes at 5 dpf (mean 162.5±4.1 per embryo) when compared to CALR-wt (mean 117.1±3.1 per embryo, P<0.001), mutant CALR-ins5 (mean 128.3±6.1 per embryo, P<0.001) and uninjected control (mean 136.7±3.0 per embryo, P<0.001), respectively.At 5 dpf, the number of cd41+ thrombocytes significantly decreased upon mpl MO knockdown (mean 43.6±4.9 per embryo) when compared to the control MO group (mean 123.5±5.9 per embryo, P<0.001) and the mutant CALR-del52 group (P<0.001). Importantly, co-injection of CALR-del52 mutant mRNA (mean 73.7±5.1 per embryo) can only partially reverse the knockdown effect of mpl MO. In contrast, the numbers of cd41+ thrombocytes did not decrease significantly upon epor MO or csf3r MO knocked-down compared with the control MO group. When CALR-del52 mutant mRNA was co-injected with epor or csf3r MOs, the numbers of cd41+ thrombocytes were comparable to those of CALR-del52-injected embryos.In Q-PCR experiments, the expression of cmyb, runx1 and scl significantly increased in only CALR-ins5 mutant group at 3 dpf when compared to 2 dpf. The expression of αeHb and βeHb significantly decreased in both CALR-del52 and CALR-ins5 mutant groups at 2 dpf but the expression of gata1 remained unchange. The effects of CALR-del52 and CALR-ins5 mutant groups on the expression of cytokine and cytokine receptor genes included the upregulation of mpl at 1 dpf followed by progressive downregulation at 2 dpf and 3 dpf but relatively stable expression of tpo and epo during early development. In the group of genes related to thrombopoiesis, the expression of emilin1a and nbeal2 was significantly downregulated in CALR-del52 group at 3 dpf when compared to 2 dpf.Conclusions: In this study, we showed that the expression of mutant CALR causes thrombocytosis through an mpl-dependent mechanism and perturbs developmental hematopoiesis in zebrafish embryos. DisclosuresNo relevant conflicts of interest to declare.

Pyrrolidino Analogues of Gefitinib with Improved EGFR Inhibition, Cancer Cell Cytotoxicity, and Pharmacokinetic Properties.

The binding mode analysis of Gefitinib revealed that 6-propylmorpholino group (sidechain) shows no interactions due to its weak electron density. In order to modify the electron density of Gefitinib's sidechain, novel pyrrolidino analogs of Gefitinib where morpholino groups were replaced by substituted pyrrolidino groups were synthesized. Gefitinib derivatives with high electronegativity atoms or groups in the pyrrolidino moiety always exhibit high potent activity against EGFR and human cancer cell lines, A431, MDA-MB-231 and A549. Among these derivatives, 16 displayed the best pharmacokinetic properties that make it to be a promising candidate for developing drugs to replace Gefitinib.

Supramolecular assemblies of moroxydine hydrochloride and cucurbit[7,8]uril

Complexes of moroxydine hydrochloride (ABOB) with cucurbit[n]urils (n = 7 or 8) were investigated using 1H NMR spectroscopy, Quadrupole-Time of Flight mass spectrometry (Q-TOF), UV absorbance spectrophotometry, isothermal titration calorimetry (ITC), and X-ray crystallography. Experimental results revealed that the morpholino group of ABOB resides within the cavity of Q[7] and Q[8] respectively in both aqueous solution and solid state. In aqueous solution, 1:1 inclusion complexes of ABOB and Q[7,8] are formed with moderate binding constants. In the solid state, the cavity of Q[8] encapsulates two ABOB morpholine groups to generate a novel 2ABOB@Q[8] inclusion complex.

Design, synthesis, and evaluation of water-soluble morpholino-decorated paclitaxel prodrugs with remarkably decreased toxicity

Novel water-soluble paclitaxel prodrugs were designed and synthesized by introducing morpholino groups through different linkers. These derivatives showed 400–20,000-times greater water solubility than paclitaxel as well as comparable activity in MCF-7 and HeLa cell lines. The prodrug PM4 was tested in the S-180 tumor mouse model, with paclitaxel as the positive control. The results showed that PM4 had comparable antitumor activity as paclitaxel, with tumor inhibition of 54% versus 56%, and remarkably decreased toxicity. The survival rate of treated mice was 8/8 in the PM4 group, compared to 3/8 in the paclitaxel group.

Trianguleniums as Optical Probes for G-Quadruplexes: A Photophysical, Electrochemical, and Computational Study.

Nucleic acids can adopt non‐duplex topologies, such as G‐quadruplexes in vitro. Yet it has been challenging to establish their existence and function in vivo due to a lack of suitable tools. Recently, we identified the triangulenium compound DAOTA‐M2 as a unique fluorescence probe for such studies. This probe's emission lifetime is highly dependent on the topology of the DNA it interacts with opening up the possibility of carrying out live‐cell imaging studies. Herein, we describe the origin of its fluorescence selectivity for G‐quadruplexes. Cyclic voltammetry predicts that the appended morpholino groups can act as intra‐ molecular photo‐induced electron transfer (PET) quenchers. Photophysical studies show that a delicate balance between this effect and inter‐molecular PET with nucleobases is key to the overall fluorescence enhancement observed upon nucleic acid binding. We utilised computational modelling to demonstrate a conformational dependence of intra‐molecular PET. Finally, we performed orthogonal studies with a triangulenium compound, in which the morpholino groups were removed, and demonstrated that this change inverts triangulenium fluorescence selectivity from G‐quadruplex to duplex DNA, thus highlighting the importance of fine tuning the molecular structure not only for target affinity, but also for fluorescence response.

Morpholino-terminated dendrimer shows enhanced tumor pH-triggered cellular uptake, prolonged circulation time, and low cytotoxicity

Short circulation is a disadvantage of dendrimers as drug delivery carriers due to their small size. In this work, pH-sensitive morpholino-terminated generation 5 poly(amido amine) (PAMAM) is prepared. At neutral pH, the dendrimer has a hydrophilic neutral surface and thereby stealth property. Under tumor acidic environments, the dendrimer develops positive charges due to protonation of the morpholino groups, and cellular uptake of the dendrimer is subsequently enhanced. The dendrimer is predicted to penetrate deeper within the tumor due to its small size (∼9 nm), and thereby the pH-sensitive function can be efficiently achieved because the microenvironment in the deeper sites is more acidic. Moreover, the morpholino-terminated PAMAM exhibited longer in vivo circulation time compared to PAMAM and hydroxyl-terminated PAMAM, partly compensating for the disadvantage of short circulation of dendrimers. Furthermore, the morpholino-terminated PAMAM also showed lower cytotoxicity than PAMAM and hydroxyl-terminated PAMAM.