Divergent Synthesis of 4-epi-Fagomine, 3,4-Dihydroxypipecolic Acid, and a Dihydroxyindolizidine and Their β-Galactosidase Inhibitory and Immunomodulatory Activities

Glycal mediated synthesis of piperidine alkaloids: fagomine, 4-epi-fagomine, 2-deoxynojirimycin, and an advanced intermediate, iminoglycal

Glucal and galactal are transformed into 2-deoxyglycolactams, which are important building blocks in the synthesis of biologically active piperidine alkaloids, fagomine and 4-epi-fagomine. In one of the strategies, reduction of 2-deoxyglycolactam-N-Boc carbonyl by lithium triethylborohydride (Super-Hydride®) has been exploited to generate lactamol whereas reduction followed by dehydration was utilized as the other strategy to functionalize the C1-C2 bond in the iminosugar substrate. The strategies provide the formal synthesis of 2-deoxynojirimycin, nojirimycin and nojirimycin B. DFT studies were carried out to determine the reason for the failure of the formation of the 2-deoxygalactonojirimycin derivative. Further, DFT studies suggest that phenyl moieties of protecting groups and lone pairs of oxygen in carbamate group plays a vital role in deciphering the conformational space of the reaction intermediates and transition-state structures through cation-π or cation-lone pair interactions. The influence of these interactions is more pronounced at low temperature when the entropy factor is small.

Synthesis of 6-Halo-Substituted Pericosine A and an Evaluation of Their Antitumor and Antiglycosidase Activities

The enantiomers of 6-fluoro-, 6-bromo-, and 6-iodopericosine A were synthesized. An efficient synthesis of both enantiomers of pericoxide via 6-bromopericosine A was also developed. These 6-halo-substituted pericosine A derivatives were evaluated in terms of their antitumor activity against three types of tumor cells (p388, L1210, and HL-60) and glycosidase inhibitory activity. The bromo- and iodo-congeners exhibited moderate antitumor activity similar to pericosine A against the three types of tumor cell lines studied. The fluorinated compound was less active than the others, including pericosine A. In the antitumor assay, no significant difference in potency between the enantiomers was observed for any of the halogenated compounds. Meanwhile, the (−)-6-fluoro- and (−)-6-bromo-congeners inhibited α-glucosidase to a greater extent than those of their corresponding (+)-enantiomers, whereas (+)-iodopericosine A showed increased activity when compared to its (−)-enantiomer.

Design, synthesis, and preliminary immunopotentiating activity of new analogues of nojirimycin

Three new classes of nojirimycin analogues viz. N-alkyl with C1-substituent (4-phenylbutyl), N-substituted 1-deoxynojirimycin and its congener δ-lactam, and a 4-phenylbutyl-β-C-glycoside were designed and synthesized for immunological studies. The resulting diverse compound library exhibited proliferation of B Cells and T cells induced by LPS and Con A, respectively. The majority of the analogues augmented the secretion of IL-12 in dendritic cells and TNF-α secretion in murine peritoneal macrophages compared to LPS (10 μg/ml). A deoxynojirimycin-triazole conjugate of phytosphingosine analogue was superior in the responses mentioned above and exhibited nitric oxide response equal to LPS. In comparison to findings on its congeners with immunosuppressive action, early immunological tests show that the novel nojirimycin analogues have immunopotentiating effect. Hence, nojirimycin analogues offer tremendous potential in tuning the immunomodulatory activity of iminosugars by subtle to substantial structural variations.

Syntheses and Glycosidase Inhibitory Activities, and in Silico Docking Studies of Pericosine E Analogs Methoxy-Substituted at C6

Inspired by the significant -glucosidase inhibitory activities of (+)- and (-)-pericosine E, we herein designed and synthesized 16 analogs of these marine natural products bearing a methoxy group instead of a chlorine atom at C6. Four of these compounds exhibited moderate -glucosidase inhibitory activities, which were weaker than those of the corresponding chlorine-containing species. The four compounds could be prepared by coupling reactions utilizing the (-)-pericosine B moiety. An additional in silico docking simulation suggested that the reason of reduced activity of the C6-methoxylated analogs might be an absence of hydrogen bonding between a methoxy group with the surrounding amino acid residues in the active site in -glucosidase.

Design And Synthesis Of An Azabicyclic Nucleoside Phosphoramidite For Oligonucleotide Antisense Constructs

We report the synthesis and biophysical evaluation of an azabicycle dinucleotide with restricted γ, β, and ε torsion angles, featuring the introduction of a piperidine ring that locks the conformation of the nucleoside into an RNA-type nucleic acid. The conceptual basis of the design is predicated upon the notion that the conformation of the phosphate group linking two RNA nucleotides can be approximated with an azabicyclic phosphoramidite which may also benefit from a unique stereoelectronic effect.

Iminosugar C-Nitromethyl Glycoside: Stereoselective Synthesis of Isoxazoline and Isoxazole-Fused Bicyclic Iminosugars

A simple and efficient method for the stereoselective synthesis of isoxazoline/isoxazole-fused iminosugar derivatives has been developed using intramolecular nitrile oxide cycloaddition (INOC) as a key step. Iminosugar C-nitromethyl glycosides, derived from simple carbohydrates, served as excellent nitrile oxide precursors in 1,3-dipolar cycloaddition reactions. N-Alkenyl iminosugar C-nitromethyl glycosides afforded novel isoxazoline-fused indolizidine-, pyrrolizidine-, and quinolizidine-based iminosugars in excellent yields with a high degree of stereoselectivity, whereas N-alkynyl iminosugar C-nitromethyl glycosides furnished the corresponding isoxazole containing tricyclic iminosugars in very good yields.

Carbohydrates in diversity-oriented synthesis: challenges and opportunities

Carbohydrates are attractive building blocks for diversity-oriented synthesis due to their stereochemical diversity and high density of polar functional groups.

d-Glucose based syntheses of β-hydroxy derivatives of l-glutamic acid, l-glutamine, l-proline and a dihydroxy pyrrolidine alkaloid

The β-hydroxy derivatives of l-glutamic acid, l-glutamine and l-proline, useful for peptide/protein studies, were synthesized starting from d-glucose.