Poly (ethylene glycol) prodrug for anthracyclines via N-Mannich base linker: Design, synthesis and biological evaluation

Mannich Bases: Centrality in Cytotoxic Drug Design

Mannich bases identified by Professor Carl Mannich have been the most extensively explored scaffolds for more than 100 years now. The versatile biological roles that they play have promoted their applications in many clinical conditions. The present review highlights the application of Mannich bases as cytotoxic agents, categorizing them into synthetic, semisynthetic and prodrugs classes and gives an exhaustive account of the work reported in the last two decades. The methods of synthesis of these cytotoxic agents, their anti-cancer potential in various cell lines and promising leads for future drug development have also been discussed. Structure-activity relationships along with the targets on which these cytotoxic Mannich bases act have been included as well.

Design and Synthesis of Polymer Prodrugs for Improving Water-Solubility, Pharmacokinetic Behavior and Antitumor Efficacy of TXA9

PURPOSE

TXA9, a novel cardiac glycoside, has a potent anti-proliferative effect against A549 human lung cancer cells, however, possesses a poor water-solubility and a rapid metabolic rate in vivo which limited the further development of TXA9. To overcome the shortcomings of TXA9, four polymer prodrugs of TXA9 were designed and synthesized.

METHODS

Poly (ethylene glycol) monomethyl ether (mPEG) and α-tocopherol polyethylene glycol succinate (TPGS) were applied to modify TXA9 via carbonate ester and glycine linkers respectively to obtain four polymer prodrugs. The water-solubility and stability of prodrugs were studied in vitro while their pharmacokinetic behaviors and antitumor activity were investigated in vivo.

RESULTS

The water-solubility of TXA9 was obviously increased and prodrugs with glycine linkers showed a better stability in rat plasma. Their pharmacokinetic investigation found that the t_1/2 and AUC_0-∞ of TPGS-Gly-TXA9 was increased by 80- and 9.6-fold compared with that of TXA9, which was more superior than the other three prodrugs. More importantly, the tumor inhibition rate of TPGS-Gly-TXA9 (43.81%) on A549 xenograft nude mice was significantly increased compared with that of TXA9 (25.26%).

CONCLUSION

The above results suggested that TPGS-Gly-TXA9 possessed better antitumor efficiency than TXA9 and could be further investigated as an anti-cancer agent.

Piperazine-azole-fluoroquinolone hybrids: Conventional and microwave irradiated synthesis, biological activity screening and molecular docking studies

A series of new 1,2,4-triazole and 1,3,4-oxadiazole derivatives was obtained via several steps sequential reactions of phenyl piperazine. Then, these compounds were converted to the corresponding fluoroquinolone hybrids via one pot three component Mannich reaction. All the reactions were examined under conventional and microwave mediated conditions, and optimum conditions were determined. The effect of different solvents and microwave power on microwave prompted reactions was investigated as well. All the newly synthesized compounds were characterized by FTIR, ¹H NMR, ¹³C NMR and EI MS spectral techniques. The antimicrobial activity, DNA gyrase and Topoisomerase IV inhibition potentials were performed. The results obtained showed that fluoroquinolone hybrids possess good antimicrobial activity. Moreover, Fluoroquinolone-azole-piperazine hybrids synthesized in the present study displayed excellent DNA gyrase inhibition. To unveil the interaction mode of compounds to receptor, a molecular docking study was performed. With an average least binding energy of -9.5 kcal/mol, all compounds were found to have remarkable inhibitory potentials against DNA gyrase (E. coli).

Microwave-assisted and conventional synthesis of novel antimicrobial 1,2,4-triazole derivatives containing nalidixic acid skeleton

Carbothioamides

Mannich bases in medicinal chemistry and drug design

The biological activity of Mannich bases, a structurally heterogeneous class of chemical compounds that are generated from various substrates through the introduction of an aminomethyl function by means of the Mannich reaction, is surveyed, with emphasis on the relationship between structure and biological activity. The review covers extensively the literature reports that have disclosed Mannich bases as anticancer and cytotoxic agents, or compounds with potential antibacterial and antifungal activity in the last decade. The most relevant studies on the activity of Mannich bases as antimycobacterial agents, antimalarials, or antiviral candidates have been included as well. The review contains also a thorough coverage of anticonvulsant, anti-inflammatory, analgesic and antioxidant activities of Mannich bases. In addition, several minor biological activities of Mannich bases, such as their ability to regulate blood pressure or inhibit platelet aggregation, their antiparasitic and anti-ulcer effects, as well as their use as agents for the treatment of mental disorders have been presented. The review gives in the end a brief overview of the potential of Mannich bases as inhibitors of various enzymes or ligands for several receptors.

Microwave-assisted synthesis of some hybrid molecules containing penicillanic acid or cephalosporanic acid moieties and investigation of their biological activities

Ethyl 4-amino-2-fluorophenylpiperazin-1-carboxylates containing a 1,3-oxazol(idin)e, 5-thioxo-1,2,4-triazole, 1,3,4-thiadiazole, 5-thioxo-1,3,4-oxadiazole, or 1,3-thiazole nucleus were obtained starting from ethyl piperazine-1-carboxylate (1) by several steps. The treatment of amine, 3 or hydrazide, 9 with several aromatic aldehydes generated the corresponding arylmethyleneamino (3a–f) or arylidenehydrazino (12a–c) compounds. The Mannich reaction between the 1,2,4-triazole or 1,3,4-oxadiazole compounds and 7-aca produced cephalosporanic acid derivatives. Penicillanic acid derivatives were obtained when 6-apa was used in the Mannich reactions. The synthesized compounds were screened for their antimicrobial, antilipase, and antiurease activities. Some of them were found to possess good-moderate antimicrobial activity against the test microorganisms. Two compounds exhibited antiurease activity, and four of them displayed antilipase activity.

Preparation of well-defined ibuprofen prodrug micelles by RAFT polymerization

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used to treat acute pain, fever, and inflammation and are being explored in a new indication in cancer. Side effects associated with long-term use of NSAIDs such as gastrointestinal damage and elevated risk of stroke, however, can limit their use and exploration in new indications. Here we report a facile method to prepare well-defined amphiphilic diblock copolymer NSAID prodrugs by direct reversible addition-fragmentation transfer (RAFT) polymerization of the acrylamide derivative of ibuprofen (IBU), a widely used NSAID. The synthesis and self-assembling behavior of amphiphilic diblock copolymers (PEG-PIBU) having a hydrophilic poly(ethylene glycol) block and a hydrophobic IBU-bearing prodrug block were investigated. Release profiles of IBU from the micelles by hydrolysis were evaluated. Furthermore, the antiproliferative action of the IBU-containing micelles in human cervical carcinoma (HeLa) and murine melanoma (B16-F10) cells was assessed.

Single-step synthesis of a new series of meso di-Mannich bases from the cyclic aminal (2S,7R,11S,16R)-1,8,10,17-tetraazapentacyclo[8.8.1.1.(8,17)0.(2,7)0(11,16)]icosane and p-substituted phenols

BACKGROUND

The results presented herein show that the cyclic aminal (2S,7R,11S,16R)-1,8,10,17-tetraazapentacyclo[8.8.1.1.(8,17)0.(2,7)0(11,16)]icosane (6), derived from cis-(meso)-1,2-diaminocyclohexane and formaldehyde, is a suitable substrate for the preption of a series of cis-meso Mannich bases such as 8a-l by reaction with p-substituted phenols 7a-l in basic media. These compounds are valuable synthetic products and may find application in asymmetric catalysis.

RESULTS

The products were characterized principally by NMR and IR spectroscopy. Both the benzylic and aminalic protons of the perhydrobenzimidazolidine moiety were diastereotopic due to the presence of stereogenic nitrogen centers. The occurrence of intramolecular hydrogen bonding interactions was confirmed by the broad OH stretching vibration band in the IR spectra. Vibrational spectra were calculated using B3LYP at 6-31G(d,p) level, and the calculated frequencies for the νOH vibrations were compared to those of the experimental spectra. Hydrogen bonding interactions in the solid state were observed through the X-ray crystallography of 8j. Additionally, Mulliken charges and Fukui indices for 6 were calculated as theoretical descriptors of electrophilicity.

CONCLUSION

A new series of meso Mannich bases called 4,4'-disubstituted-2,2'-{[(3aR,7aS)-2,3,3a,4,5,6,7,7a-octahydro-1H-1,3-benzimidazole-1,3-diyl]bis(methylene)} diphenols (8a-l) which are derived from cis-(meso)-1,2-diaminocyclohexane, were obtained from cyclic aminal 6. These results confirmed the behavior of 6 as an electrophilic preformed reagent in Mannich reactions in basic media.

Antifungal activity of fused Mannich ketones triggers an oxidative stress response and is Cap1-dependent in Candida albicans

We investigated the antifungal activity of fused Mannich ketone (FMK) congeners and two of their aminoalcohol derivatives. In particular, FMKs with five-membered saturated rings were shown to have minimum inhibitory concentration (MIC90s) ranging from 0.8 to 6 µg/mL toward C. albicans and the closely related C. parapsilosis and C. krusei while having reduced efficacy toward C. glabrata and almost no efficacy against Aspergillus sp. Transcript profiling of C. albicans cells exposed for 30 or 60 min to 2-(morpholinomethyl)-1-indanone, a representative FMK with a five-membered saturated ring, revealed a transcriptional response typical of oxidative stress and similar to that of a C. albicans Cap1 transcriptional activator. Consistently, C. albicans lacking the CAP1 gene was hypersensitive to this FMK, while C. albicans strains overexpressing CAP1 had decreased sensitivity to 2-(morpholinomethyl)-1-indanone. Quantitative structure-activity relationship studies revealed a correlation of antifungal potency and the energy of the lowest unoccupied molecular orbital of FMKs and unsaturated Mannich ketones thereby implicating redox cycling-mediated oxidative stress as a mechanism of action. This conclusion was further supported by the loss of antifungal activity upon conversion of representative FMKs to aminoalcohols that were unable to participate in redox cycles.

PEG-scutellarin prodrugs: synthesis, water solubility and protective effect on cerebral ischemia/reperfusion injury

Fifteen PEG-scutellarin prodrugs were synthesized by modifying carboxyl and phenolic hydroxyl groups of scutellarin with mPEG of different molecular weight (400-3000). The water solubility of prodrugs increased remarkably and reached the maximum value of 783.88 mg/mL (scutellarin, 0.02 mg/mL). The anti-infarct effects of four PEG prodrugs with high water solubility were evaluated by Cerebral Ischemia/Reperfusion in the Middle Cerebral Artery Occlusion (MCAO) model. The results showed that the prodrug 7e could significantly reduce the infarct area from 27.2% to 12.2% (33.3% for the control) and decrease the neurological deficit score from 2.77 to 1.32 (2.85 for the control). The half-life (18.62 min) of the prodrug 7e was significantly longer than that of scutellarin (3.03 min).