Synthesis of an Adenine Nucleoside Containing the (8′R) Epimeric Carbohydrate Core of Amipurimycin and Its Biological Study

Solving the Structural Puzzles of Amipurimycin and Miharamycins Enabled by Stereodivergent Total Synthesis

The efforts toward the synthesis of amipurimycin and miharamycin A/B, two peptidyl nucleoside antibiotics bearing a unique nine carbon C3-branched pyranosyl amino acid core, are accounted. Highlighted is our stereodivergent total synthesis of all the possible diastereoisomers of amipurimycin, which has enabled us to solve the structural puzzles of amipurimycin and miharamycin A/B after ∼50 years of their discovery.

The Miharamycins and Amipurimycin: their Structural Revision and the Total Synthesis of the Latter

The structural puzzle of amipurimycin, a peptidyl nucleoside antibiotic, is solved by total synthesis and X-ray diffraction analysis, with the originally proposed configurations at C3' and C8' inverted and those at C6', C2'', and C3'' corrected. A similar structural revision of the relevant miharamycins is proposed via chemical transformations and then validated by X-ray diffraction analysis. The miharamycins bear an unusual trans-fused dioxabicyclo[4.3.0]nonane sugar scaffold, which was previously assigned as being in the cis configuration.

Identification of the Amipurimycin Gene Cluster Yields Insight into the Biosynthesis of C9 Sugar Nucleoside Antibiotics

Feeding studies indicate a possible synthetic pattern for the N-terminal cis-aminocyclopentane carboxylic acid (ACPC) and suggest an unusual source of the high-carbon sugar skeleton of amipurimycin (APM). The biosynthetic gene cluster of APM was identified and confirmed by in vivo experiments. A C9 core intermediate was discovered from null mutants of ACPC pathway, and an ATP-grasp enzyme (ApmA8) was reconstituted in vitro for ACPC loading. Our observations allow a first proposal of the APM biosynthetic pathway.

Protein tyrosine phosphatase 1B and α-glucosidase inhibitory activities of Pueraria lobata root and its constituents

ETHNOPHARMACOLOGICAL RELEVANCE

Pueraria lobata root was used to treat wasting-thirst regarded as diabetes mellitus and was included in the composition of Okcheonsan, which is prescribed for thirst-waste in traditional Chinese medicine.

AIM OF THE STUDY

The objective of this study was to evaluate the anti-diabetic potential of the root of Pueraria lobata and its constituents via protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase inhibitory activities.

MATERIALS AND METHODS

In this study, anti-diabetic activities of the 70% ethanolic (EtOH) extract from P. lobata roots and its solvent soluble fractions with the isolated compounds were investigated by evaluating in vitro PTP1B and α-glucosidase inhibitory activities. We also examined the potentials of active compounds as PTP1B and α-glucosidase inhibitors via enzyme kinetics and in silico molecular docking simulation between the enzymes and active compounds.

RESULTS

Triterpenoids lupeol and lupenone were potent PTP1B inhibitors with IC₅₀ values of 38.89±0.17 and 15.11±1.23μM. Kinetic study using the Lineweaver-Burk and Dixon plots demonstrated that these compounds showed a noncompetitive-type inhibition against PTP1B with respective K_i values of 13.88μM and 21.24μM. In addition, molecular docking simulation showed lupeol and lupenone has negative binding energy values of -8.03 and -8.56kcal/mol. Considering the α-glucosidase inhibitory potential, daidzein, genistein, and calycosin exhibited the most potent α-glucosidase inhibition with IC₅₀ values of 8.58±0.94, 2.37±0.52 and 6.84±1.58μM, respectively. Kinetic study demonstrated that these 3 compounds showed a noncompetitive-type inhibition against α-glucosidase with respective K_i values of 17.64μM, 5.03μM and 13.83μM. Moreover, molecular docking simulation showed daidzein, genistein and calycosin has more lower binding energy (-7.16kcal/mol, -7.42kcal/mol and -7.31kcal/mol) with higher binding affinity and tight binding capacity in the molecular docking studies than standard ligand α-D-glucose (-6.74kcal/mol).

CONCLUSION

Our results of the present study clearly demonstrate the potential of P. lobata extract and its constituents to inhibit PTP1B and α-glucosidase, contributing to the development of therapeutic or preventive agents that can be used in the treatment of diabetes.

Synthesis of the C8'-epimeric thymine pyranosyl amino acid core of amipurimycin

The C8'-epimeric pyranosyl amino acid core 2 of amipurimycin was synthesized from D-glucose derived alcohol 3 in 13 steps and 14% overall yield. Thus, the Sharpless asymmetric epoxidation of allyl alcohol 7 followed by trimethyl borate mediated regio-selective oxirane ring opening with azide, afforded azido diol 10. The acid-catalyzed 1,2-acetonide ring opening in 10 concomitantly led to the formation of the pyranose ring skeleton to give 2,7-dioxabicyclo[3.2.1]octane 12. Functional group manipulation in 12 gave 21 that on stereoselective β-glycosylation afforded the pyranosyl thymine nucleoside 2 - a core of amipurimycin.

Antiproliferative activity of bicyclic benzimidazole nucleosides: synthesis, DNA-binding and cell cycle analysis

Bicyclic benzimidazole nucleosides were synthesized from d-glucose as a starting material. DNA binding, antiproliferative activity and cell cycle analysis were performed.

d-Glucose based synthesis of proline–serine C–C linked central and right hand core of a kaitocephalin-a glutamate receptor antagonist

Synthesis of the proline–serine core of kaitocephalin starting from d-glucose, utilizing the Jocic–Reeve and Corey–Link reaction sequence as key steps.

New antitumor 6-chloropurine nucleosides inducing apoptosis and G2/M cell cycle arrest

Treating cancer has been challenging for decades, following countless approaches and attempts. Nucleosides, alone or as part of nucleotides, are vital elements of living systems and have shown pharmacological effects, e.g. as antibiotic or antiviral agents. We investigated the antitumor potential on human melanoma, lung and ovarian carcinomas, and on colon adenocarcinoma of a new series of purine nucleosides based on a 6-chloropurine or a 2-acetamido-6-chloropurine scaffold linked to perbenzylated hexosyl (glucosyl, galactosyl and mannosyl) residues. All compounds were tested in a sulforhodamine B (SRB) assay for their cytotoxicity and provided micromolar GI50 values with order of magnitude comparable to structurally similar chemotherapeutics, namely 2-chloro-2'-deoxyadenosine (cladribine). Furthermore, the induction of apoptosis was established and cell cycle analysis was accomplished demonstrating a G2/M cell cycle arrest.

Diosgenin from Dioscorea bulbifera: novel hit for treatment of type II diabetes mellitus with inhibitory activity against α-amylase and α-glucosidase

Diabetes mellitus is a multifactorial metabolic disease characterized by post-prandial hyperglycemia (PPHG). α-amylase and α-glucosidase inhibitors aim to explore novel therapeutic agents. Herein we report the promises of Dioscorea bulbifera and its bioactive principle, diosgenin as novel α-amylase and α-glucosidase inhibitor. Among petroleum ether, ethyl acetate, methanol and 70% ethanol (v/v) extracts of bulbs of D. bulbifera, ethyl acetate extract showed highest inhibition upto 72.06 ± 0.51% and 82.64 ± 2.32% against α-amylase and α-glucosidase respectively. GC-TOF-MS analysis of ethyl acetate extract indicated presence of high diosgenin content. Diosgenin was isolated and identified by FTIR, 1H NMR and 13C NMR and confirmed by HPLC which showed an α-amylase and α-glucosidase inhibition upto 70.94 ± 1.24% and 81.71 ± 3.39%, respectively. Kinetic studies confirmed the uncompetitive mode of binding of diosgenin to α-amylase indicated by lowering of both Km and Vm. Interaction studies revealed the quenching of intrinsic fluorescence of α-amylase in presence of diosgenin. Similarly, circular dichroism spectrometry showed diminished negative humped peaks at 208 nm and 222 nm. Molecular docking indicated hydrogen bonding between carboxyl group of Asp300, while hydrophobic interactions between Tyr62, Trp58, Trp59, Val163, His305 and Gln63 residues of α-amylase. Diosgenin interacted with two catalytic residues (Asp352 and Glu411) from α-glucosidase. This is the first report of its kind that provides an intense scientific rationale for use of diosgenin as novel drug candidate for type II diabetes mellitus.