Polyhydroxylated alkaloids -- natural occurrence and therapeutic applications

Design, synthesis and in vitro microbiological evaluation of 6,6-dimethyl-7,9-diaryl-1,2,4,8-tetraazaspiro[4.5]decan-3-thiones--a new series of 'tailor-made' compounds

Some novel 'tailor-made' compounds, 6,6-dimethyl-7,9-diaryl-1,2,4,8-tetraazaspiro[4.5]decan-3-thiones 23-27 have been studied for their in vitro antibacterial activity against Staphylococcus aureus, beta-Heamolytic streptococcus, Vibreo cholerae, Salmonella typhii, Shigella felxneri, Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa and anti-fungal activity against Aspergillus flavus, Mucor, Rhizopus and Microsporum gypsuem. Compounds 24 and 25 exerted potent antibacterial activity against S. aureus, beta-H. streptococcus, E. coli and P. aeruginosa whereas all compounds 23-27 exerted strong in vitro antifungal activity against A. flavus, Mucor and Rhizopus.

Discovery of antimycobacterial spiro-piperidin-4-ones: an atom economic, stereoselective synthesis, and biological intervention

An atom economic and stereoselective synthesis of several spiro-piperidin-4-ones through 1,3-dipolar cycloaddition of azomethine ylides generated in situ from isatin and alpha-amino acids viz . proline, phenylglycine, and sarcosine to a series of 1-methyl-3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones is described. These compounds were evaluated for their in vitro and in vivo activity against Mycobacterium tuberculosis H37Rv (MTB), multidrug resistant Mycobacterium tuberculosis (MDR-TB), and Mycobacterium smegmatis (MC(2)). Compound 4-(4-fluorophenyl)-5-phenylpyrrolo(spiro[2.3'']oxindole)spiro[3.3']-1'-methyl-5'-(4-fluorophenylmethylidene)piperidin-4'-one (4e) was found to be the most active in vitro with a MIC value of 0.07 microM against MTB and was 5.1 and 67.2 times more potent than isoniazid and ciprofloxacin, respectively. In vivo, compound 4e decreased the bacterial load in lung and spleen tissues with 1.30 and 3.73-log 10 protections respectively and was considered to be promising in reducing bacterial count in lung and spleen tissues.

Phenylethyl cinnamides: a new series of alpha-glucosidase inhibitors from the leaves of Aegle marmelos

A series of phenylethyl cinnamides, which included new compounds named anhydromarmeline, aegelinosides A and B, were isolated from Aegle marmelos leaves as alpha-glucosidase inhibitors. The structures of new compounds were characterized by spectroscopic data and chemical degradation. Of compounds isolated, anhydroaegeline revealed the most potent inhibitory effect against alpha-glucosidase with IC(50) value of 35.8 microM. The present result also supports ethnopharmacological use of A. marmelos as a remedy for diabetes mellitus.

Unexpected formation of 3-chloro-1-hydroxy-2,6-diarylpiperidin-4-ones: synthesis, antibacterial and antifungal activities

New 3-chloro-1-hydroxy-2,6-diarylpiperidin-4-ones 18-22 were synthesized, characterized by melting point, elemental analysis, MS, FT-IR, one-dimensional NMR ((1)H & (13)C) spectroscopic data and evaluated for their in vitro antibacterial and antifungal activities. All the newly synthesized compounds exerted a wide range of antibacterial activities against the entire tested gram-positive and gram-negative bacterial strains except Escherichia coli. Compounds 21 and 22 exerted strong antifungal activities against Aspergillus flavus, mucor and Microsporum gypsuem. In addition, compound 20 was more potent against Rhizopus.

In vitro inhibition of glycogen-degrading enzymes and glycosidases by six-membered sugar mimics and their evaluation in cell cultures

We investigated in vitro inhibition of mammalian carbohydrate-degrading enzymes by six-membered sugar mimics and their evaluation in cell cultures. 1-Deoxynojirimycin (DNJ) showed no significant inhibition toward glycogen phosphorylase (GP) but was a potent inhibitor of another glycogen-degrading enzyme, amylo-1,6-glucosidase (1,6-GL), with an IC(50) value of 0.16 microM. In primary rat hepatocytes, the inhibition of glycogen breakdown by DNJ reached plateau at 100 microM with 25% inhibition and then remained unchanged. The potent GP inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol (D-AB1) inhibited hepatic glucose production with an IC(50) value of about 9 microM and the inhibition by D-AB1 was further enhanced in the presence of DNJ. DNJ and alpha-homonojirimycin (HNJ) are very potent inhibitors of rat intestinal maltase, with IC(50) values of 0.13 and 0.08 microM, respectively, and also showed a similar strong inhibition toward maltase in Caco-2 cell model system, with IC(50) value of 0.05 and 0.10 microM, respectively. D-Isofagomine (D-IFG) and L-IFG are competitive and noncompetitive inhibitors of human lysosomal beta-glucosidase (beta-GL), respectively, with K(i) values of 8.4 nM and 6.9 microM. D-IFG increased intracellular beta-GL activity by twofold at 10 microM in Gaucher N370S cell line as an 'active-site-specific' chaperone, and surprisingly a noncompetitive inhibitor L-IFG also increased intracellular beta-GL activity by 1.6-fold at 500 microM.

Iminosugars from Baphia nitida Lodd

Chromatographic separation of the 50% aqueous EtOH extract of the leaves of the African medicinal tree Baphia nitida resulted in isolation of 10 iminosugars. The plant contained 2R,5R-dihydroxymethyl-3R,4R-dihydroxypyrrolidine (DMDP) as a major alkaloid. The structure of a new alkaloid was also elucidated by spectroscopic methods as the 1-O-beta-D-fructofuranoside of DMDP, and this plant produced 3-O-beta-D-glucopyranosyl-DMDP as well. DMDP is a potent inhibitor of beta-glucosidase and beta-galactosidase, whereas the other two derivatives lowered inhibition toward both of these enzymes and improved inhibitory activities toward rice alpha-glucosidase and rat intestinal maltase.

Selective Metabolism of Glycosidase Inhibitors by a Specialized Moth Feeding on Hyacinthoides non-scripta Flowers

The British moth Eana incanana (Tortricidae) has been found to selectively metabolize the glycosidase inhibitor 2 R, 3 R, 4 R, 5 R-2,5-dihydroxymethyl-3,4-dihydroxypyrrolidine (DMDP), whereas it excretes related alkaloids from Hyacinthoides non-scripta (Hyacinthaceae). Very few native animals feed on H. non-scripta, but the larvae of E. incanana are specialized herbivores feeding just on the buds and flowers destroying the ovary. DMDP is the major glucosidase inhibitor of H. non-scripta and the moth may overcome inhibition of digestive glucosidases by metabolizing the DMDP. The glucosidase enzymes of the caterpillar are inhibited by DMDP. The caterpillar excretes the other glycosidase inhibitors produced by this plant and the frass has increased concentrations of these alkaloids.

Annona muricata (Graviola): Toxic or Therapeutic

The medicinal plant Annona muricata (Annonaceae), also known as Graviola or Soursop, is reported here to contain imino sugar alkaloids. This is the first report of imino sugars in the Annonaceae. Graviola has very broad medicinal claims and is also widely consumed as a food and in drinks in the tropics. The plant produces a wide range of secondary chemicals, some already known to be toxic, but the discovery here of the imino sugars as a new group of chemicals, including the neurotoxin swainsonine, raises questions about the safety of consumption of this plant.

Synthesis of densely functionalized enantiopure indolizidines by ring-closing metathesis (RCM) of hydroxylamines from carbohydrate-derived nitrones

Background

Indolizidine alkaloids widely occur in nature and display interesting biological activity. This is the reason for which their total synthesis as well as the synthesis of non-natural analogues still attracts the attention of many research groups. To establish new straightforward accesses to these molecules is therefore highly desirable.

Results

The ring closing metathesis (RCM) of enantiopure hydroxylamines bearing suitable unsaturated groups cleanly afforded piperidine derivatives in good yields. Further cyclization and deprotection of the hydroxy groups gave novel highly functionalized indolizidines. The synthesis of a pyrroloazepine analogue is also described.

Conclusion

We have developed a new straightforward methodology for the synthesis of densely functionalized indolizidines and pyrroloazepine analogues in 6 steps and 30–60% overall yields from enantiopure hydroxylamines obtained straightforwardly from carbohydrate-derived nitrones.

5''-(4-Chloro-benzyl-idene)-1',1''-dimethyl-3'-phenyl-acenaphthene-1-spiro-2'-pyrrolidine-3'-spiro-3''-pyridine-2,4''-dione

In the title compound, C₃₄H₂₈Cl₂N₂O₂, the five-membered pyrrolidine ring adopts an envelope conformation and the six-membered piperidinone ring is in a distorted half-chair conformation. The mol­ecular structure shows three intra­molecular C—H⋯O inter­actions and the crystal packing is stabilized through inter­molecular C—H⋯O and C—H⋯π inter­actions.

A Convergent Pd-Catalyzed Asymmetric Allylic Alkylation ofdl- andmeso-Divinylethylene Carbonate: Enantioselective Synthesis of (+)-Australine Hydrochloride and Formal Synthesis of Isoaltholactone

The use of a mixture of dl- and meso-divinylethylene carbonate as an electrophile in palladium-catalyzed asymmetric allylic alkylation reactions is reported. From the diastereomeric mixture of meso and chiral racemic starting materials, a single product is obtained in high optical purity employing either oxygen or nitrogen nucleophiles. The resulting dienes have proven to be versatile synthetic intermediates as each carbon is functionalized for further transformation and differentiated by virtue of the reaction. A mechanism for this intriguing transformation is proposed and a concise enantioselective total synthesis of (+)-australine hydrochloride is reported as well as a formal synthesis of isoaltholactone.

A divergent asymmetric approach to aza-spiropyran derivative and (1S,8aR)-1-hydroxyindolizidine

Background

Spiroketals and the corresponding aza-spiroketals are the structural features found in a number of bioactive natural products, and in compounds possessing photochromic properties for use in the area of photochemical erasable memory, self-development photography, actinometry, displays, filters, lenses of variable optical density, and photomechanical biomaterials etc. And (1R,8aS)-1-hydroxyindolizidine (3) has been postulated to be a biosynthetic precursor of hydroxylated indolizidines such as (+)-lentiginosine 1, (−)-2-epilentiginosine 2 and (−)-swainsonine, which are potentially useful antimetastasis drugs for the treatment of cancer. In continuation of a project aimed at the development of enantiomeric malimide-based synthetic methodology, we now report a divergent, concise and highly diastereoselective approach for the asymmetric syntheses of an aza-spiropyran derivative 7 and (1S,8aR)-1-hydroxyindolizidine (ent-3).

Results

The synthesis of aza-spiropyran 7 started from the Grignard addition of malimide 4. Treatment of the THP-protected 4-hydroxybutyl magnesium bromide with malimide 4 at −20°C afforded N,O-acetal 5a as an epimeric mixture in a combined yield of 89%. Subjection of the diastereomeric mixture of N,O-acetal 5a to acidic conditions for 0.5 h resulted in the formation of the desired functionalized aza-spiropyran 7 as a single diastereomer in quantitative yield. The stereochemistry of the aza-spiropyran 7 was determined by NOESY experiment. For the synthesis of ent-3, aza-spiropyran 7, or more conveniently, N,O-acetal 5a, was converted to lactam 6a under standard reductive dehydroxylation conditions in 78% or 77% yield. Reduction of lactam 6a with borane-dimethylsulfide provided pyrrolidine 8 in 95% yield. Compound 8 was then converted to 1-hydroxyindolizidine ent-3 via a four-step procedure, namely, N-debenzylation/O-mesylation/Boc-cleavage/cyclization, and O-debenzylation. Alternatively, amino alcohol 8 was mesylated and the resultant mesylate 12 was subjected to hydrogenolytic conditions, which gave (1S,8aR)-1-hydroxyindolizidine (ent-3) in 60% overall yield from 8.

Conclusion

By the reaction of functionalized Grignard reagent with protected (S)-malimide, either aza-spiropyran or (1S,8aR)-1-hydroxyindolizidine skeleton could be constructed in a concise and selective manner. The results presented herein constitute an important extension of our malimide-based synthetic methodology.

Occurrence of orally administered mulberry 1-deoxynojirimycin in rat plasma

1-deoxynojirimycin (DNJ), a potent glucosidase inhibitor, is a characteristic constituent of the mulberry leaf. Dietary mulberry DNJ may be beneficial for the suppression of abnormally high blood glucose levels, thereby preventing diabetes mellitus. Although there is considerable interest in the effects of mulberry DNJ, the intestinal absorption and pharmacokinetic profile of orally administered mulberry DNJ have never been characterized. In this study, we developed a method for determining the level of plasma DNJ by hydrophilic interaction chromatography coupled to a mass spectrometric detector (HILIC-MS) to investigate the absorption and metabolism of orally administered mulberry DNJ in rats. DNJ was separated from plasma extract on a TSK gel Amide-80 column, a representative column for HILIC. At postcolumn, DNJ was concurrently detected and identified by MS. The plasma DNJ concentration in fasted rats was below the detection limit [<1 microg (6 nmol)/mL]; however, the concentration reached a maximum [15 microg (92 nmol)/mL] 30 min after the administration of mulberry DNJ (110 mg/kg of body weight), and the DNJ concentration decreased rapidly thereafter. When the rats received different amounts of mulberry DNJ (1.1, 11, and 110 mg/kg of body weight), dose-dependent incorporation of DNJ into the plasma was confirmed. We did not detect any DNJ metabolites in the plasma. These findings indicate that orally administered mulberry DNJ is absorbed as an intact form from the alimentary tract and then is quickly excreted from the body. The developed HILIC-MS method could be applied in determining levels of DNJ in urine and tissues, and therefore, the method would be a powerful tool for studying the metabolic fate of mulberry DNJ as well as its bioavailability.