Nisachon Khunnawutmanotham’s research while affiliated with Chulabhorn Research Institute and other places

Due to the rising prevalence of Alzheimer's disease (AD), there is a pressing need for more effective drugs to treat or manage AD's symptoms. Studies have shown that cholinesterase inhibition can improve cognitive and behavioral symptoms associated with AD, by addressing the cholinergic deficit. Based on the recent development of cholinesterase inhibitors with indoloquinoline and triazole moiety, we rationalized that compounds with an isocryptolepine‐triazole scaffold may also have the same biological targets. In this study, eighteen previously synthesized isocryptolepine‐triazole compounds were assessed for their ability to inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The majority of these compounds demonstrated potent selective AChE inhibition. Furthermore, our molecular docking and molecular dynamic simulation studies reveal that the isocryptolepine and triazole moieties are important for the binding of the compounds with the periphery of the AChE's binding pocket. While reductions in molecular weights and lipophilicities may be necessary to improve their pharmacokinetic properties, this work provides valuable insights for designing future AChE inhibitors, based on the novel isocryptolepine‐triazole scaffold.

It's not straightforward to separate indole alkaloids from kratom (Mitragyna speciosa). Two of the most common issues are broadening peak form and the inability to yield baseline separation of closely related structures. Mitragynine (MG), speciogynine (SG), speciociliatine (SC), and paynantheine (PT) are the four major alkaloids discovered in kratom. MG, SC, and SG are diastereomeric isomers, and PT is a dehydro counterpart of SG. Column selectivity, which is closely related to column selection, has a significant impact on analysis completion. The AQS C18, UPS C18, Integral C18, Luna Omega PS C18 and pHendure C18 columns were evaluated in a mobile phase of acetonitrile-water containing ammonium acetate. AQS C18, embedded polar groups (EPGs) C18, produced the best results of all the columns tested. The impact of ammonium acetate buffer concentration was also investigated. The best conditions were 60% acetonitrile in water with a buffer of 10 mM ammonium acetate. In this condition, a good peak form with baseline separation was obtained in isocratic mode with a total analysis time of less than 11 minutes. Keywords: Mitragyna speciosa, indole alkaloids, column selection, embedded polar groups (EPGs) C18, ammonium acetate

Mitragyna speciosa, also known as "kratom" in Thai, is a Southeast Asian tree whose leaves are used to induce stimulant and opioid-like analgesic effects. With the goal of standardization and quality control of raw kratom, an HPLC-UV method was devised for quantification of four important indole alkaloids: mitragynine, paynantheine, speciogynine, and speciociliatine. Paynantheine is a dehydro analog of speciogynine, whereas mitragynine, speciogynine, and speciociliatine are diastereomers. An ethanol-water mobile phase system containing ammonium acetate was used in conjunction with a UPS-C18 column in the "greening chromatographic approach." Mobile phase compositions, column temperature, and ammonium acetate buffer concentration were all studied to provide baseline separation of all four indole alkaloids. The best chromatographic conditions were 15 mM ammonium acetate in 55% (v/v) ethanol in water at 40°C in isocratic mode. The total analysis time in this case was less than 8.5 minutes. The optimized method was utilized to separate the indole-type alkaloids in raw fresh kratom leaves. The Eco-scale was used to evaluate the method's environmental friendliness.

Eighteen hybrid compounds between 8‐bromo‐2‐fluoro‐isocryptolepine (4) and 1,2,3‐triazole were synthesized via azide rearrangement‐annulation reaction. Compound 4 underwent regioselective N‐propargylation and click reaction to form 8‐bromo‐2‐fluoro‐isocryptolepine‐triazole hybrids 11 which were evaluated for cytotoxic activity. Compound 11 c containing 1‐anisyltriazole was the most effective in inhibiting HepG2, HuCCA‐1 and A549 cell lines (IC50 values of 1.65–3.07 μM) while compounds 11 a (1‐phenyltriazole), 11 j (1‐para‐CF3‐benzyltriazole) and 11 l (1‐meta‐Cl‐benzyltriazole) were potent inhibitors of HuCCA‐1, HepG2 and A549 cell lines, respectively. Moreover, 11 l showed the lowest cytotoxicity to normal human kidney cell line. Compounds 11 c and 11 l provided improvement of cytotoxic activity over 4. Compounds 4, 11 c and 11 l were selected to investigate their mechanisms of action. The results showed that 4 could induce G2/M cell cycle arrest and was involved in the upregulation of p53 and p21 proteins. However, the mechanisms of growth inhibition by 11 c and 11 l were associated with G0/G1 cell cycle arrest and mediated by induction of oxidative stress.

The study presented a facile and efficient extraction method of main indole alkaloids from the fresh leaves of Mitragyna speciosa. A water extract containing three main indole alkaloids, namely mitragynine (MG), paynantheine (PT), and speciogynine (SG), was obtained by boiling the fresh leaves in water followed by partitioning with dichloromethane. The extraction yield of 1.0 % (w/w) was obtained under the optimized conditions. The contents of MG, PT, and SG obtained from water extraction were determined by high‐performance liquid chromatography analysis and were found to be comparable to those obtained from methanol extraction. However, because the extraction yield obtained from using methanol was tenfold higher than that from using hot water, this indicated the presence of some undesirable materials in the methanol but not in water extract. This method provided an alkaloid‐rich extract of M. speciosa. The procedure was easy to perform, inexpensive, environmentally benign, and could be easily scaled up from laboratory to industrial scale.

Acridine-based compounds possess anticancer activities by intercalating to DNA. Although they have chemotherapeutic potential, acridine-based compounds are not used to treat cancer. In this study, 2, N ¹⁰ -acridone derivatives are designed and synthesized based on acridone, a ketone derivative of acridine. Herein, acridone is functionalized with alkyl side chains containing terminal nitrogen-based moieties at the N ¹⁰ -position and substituted at the C2-position. The products are evaluated for in vitro cytotoxicity against four cancer cell lines: Molt-3, HepG2, A549, and HuCCA-1. The derivative bearing two butyl piperidine side chains at the C2- and N ¹⁰ -positions is the most active, with IC 50 values ranging from 2.96 to 9.46 µM. Molecular modeling studies supported the binding of the derivatives to DNA by intercalation, thereby confirming the observed cytotoxic effects.

Experimental details, characterization data and copies of NMR spectra.

A series of 3-amino-6,7-dimethoxycoumarins conjugated with the N-benzylpyridinium moiety through an amide-bond linkage was synthesized and evaluated for their acetylcholinesterase inhibitory activity. A number of the benzylpyridinium derivatives exhibited potent activities with inhibitory concentration (IC50) values in the nanomolar concentration range. Among them, the 2,3-difluorobenzylpyridinium-containing compound was the most potent inhibitor with an IC50 value of 1.53 ± 0.01 nM. Docking studies revealed that the synthesized compounds inhibit the target enzyme by a dual binding site mechanism whereby the coumarin portion binds with the peripheral anionic site while the N-benzylpyridinium residue binds with the catalytic anionic site of the enzyme.