An asymmetric aminohydroxylation route to cis-2,6-disubstituted piperidine-3-ol: application to the synthesis of (−)-deoxocassine

Regioselective ring opening of aziridine for synthesizing azaheterocycle

Aziridine had different regioselective ring openings depending on the functional group of its alkyl substituent. In the case of the alkyl group bearing γ-ketone at the C2 substituent of aziridine, the ring opening by the hydroxy nucleophile from H2O occurred by attacking the aziridine carbon at the C2 position. This reaction proceeded efficiently in the presence of CF3CO2H. Interestingly, the same starting aziridine ring bearing the alkyl substituent at the C2 position with the γ-silylated hydroxy group instead of γ-ketone led to the ring-opening reaction by the same oxygen nucleophile at the unsubstituted C3 position, with the breakage of the bond between aziridine N1 nitrogen and carbon at C3. These reaction products were cyclized to afford substituted pyrrolidine and piperidine rings with representative examples of congeners of pseudoconhydrine and monomorine.

Synthesis and potential antidiabetic and lipid-lowering activities of putative asperidine B and its desmethyl analogue

Putative asperidine B is an unnatural 2,6-disubstituted piperidin-3-ol and a structural isomer of (+)-preussin, a well-known pyrrolidin-3-ol alkaloid. This work reports the first enantioselective synthesis of putative asperidine B and its desmethyl analogue via a chiron approach starting from d-isoascorbic acid as well as evaluation of their free-radical scavenging, antidiabetic, and anti-hyperlipidemic activities. Both putative asperidine B and its desmethyl analogue markedly reduced the total reactive oxygen species (ROS) without cytotoxicity in hepatocellular carcinoma (HepG2) cells. The desmethyl analogue was a potent inducer for two antioxidant gene expression, glutathione peroxidase and superoxide dismutase, whereas putative asperidine B only induced superoxide dismutase. In addition, putative asperidine B exerted potent antidiabetic activity via α-glucosidase inhibition (IC50 = 0.143 ± 0.001 mg/mL) comparable to that of acarbose, an antidiabetic drug. Consistent with the parent asperidine B (preussin), both putative asperidine B and its desmethyl analogue inhibited cholesterol absorption in the intestinal Caco-2 cells. These novel and promising antioxidant, antidiabetic, and lipid-lowering effects of piperidin-3-ols could offer a starting point for this class of compounds for obesity and diabetic drug discovery.

Application of asymmetric Sharpless aminohydroxylation in total synthesis of natural products and some synthetic complex bio-active molecules

This report illustrates the applications of Asymmetric Sharpless Aminohydroxylation (ASAH) in the stereoselective synthesis of vicinal amino alcohols as important intermediates in the total synthesis of complex molecules and natural products with significant biological activities. The ASHA allows the regio- syn-selective synthesis of 1,2-amino alcohols via reaction of alkenes with salts of N-halosulfonamides, -amides and -carbamates employing osmium tetroxide (OsO4) as an efficient catalyst. In this reaction, chirality is induced via the addition of dihydroquinine- and dihydroquinidine as derived chiral ligands.

One-pot multiple reactions: asymmetric synthesis of 2,6-cis-disubstituted piperidine alkaloids from chiral aziridine

A divergent, new, and highly stereoselective synthesis of cis-2,6-disubstituted piperidine natural products including isosolenopsins, deoxocassine, and spectaline was achieved from chiral aziridine decorated with appropriate alkyl chains for isosolenopsins or alkynyl groups for deoxocassine and spectaline at C2. The characteristic feature of this synthesis is one-pot sequential reactions under atmospheric hydrogen including the reduction of alkyne (for deoxocassine and spectaline), reductive ring-opening of aziridine, debenzylation, and intramolecular reductive amination in high yields. The prerequisite aziridines were elaborated from commercially available (2S)-hydroxymethylaziridine through oxidation, Wittig olefination, and the Grignard reaction for isosolenopsins or substrate-controlled lithium alkynylate addition for deoxocassine and spectaline.