Reversal of anticancer drug resistance by COTC based on intracellular glutathione and glyoxalase I

Chemoselective Nozaki-Hiyama-Takai-Kishi and Grignard reaction: short synthesis of some carbahexopyranoses

A common, divergent, efficient, stereoselective and short approach for the total syntheses of some carbahexopyranoses namely, MK7607, (-)-gabosine A, (-)-conduritol E, (-)-conduritol F, 6a-carba-β-d-fructopyranose and other carbasugars using chemoselective Grignard or Nozaki-Hiyama-Takai-Kishi (NHTK) reactions and RCM. Herein, the Grignard and NHTK reactions are able to differentiate the reactivity difference between lactol or lactolacetate and aldehyde of 2 & 6 under given conditions to give the desired skeleton chemoselectivity.

Enantioselective Synthesis of a New Non-Natural Gabosine

The preparation of a new non-natural gabosine is reported, in which the chirality is transferred from the toluene’s biotransformed metabolite (1R,2S)-3-methylcyclohexa-3.5-diene-1,2-diol. Further chemical transformations to introduce additional functionality and chirality to the molecule were also accomplished.

A divergent strategy to synthesize gabosines featuring a switchable two-way aldol cyclization

Gabosines and their natural analogues, belonging to C7 carbasugars, have attracted great attention in synthesis due to their rich structural variety and promising biological activities. A new diversity-oriented approach for the gabosine-type carbasugars based on a tunable regioselective aldol cyclization of flexible precursor 2 is explored. Two cyclization modes (A and B) of the precursor can be well controlled by switching promoters to selectively produce two resulting cyclohexa(e)nones 3 and 10, both of which are versatile intermediates for various C7 carbasugars. After the conversion of 3 to eight natural carbasugars, the utility of intermediate 10 is illustrated by the first synthesis of (-)-gabosine L, as well as the new synthesis of (-)-gabosine A, (-)-gabosine B, (-)-gabosine N and (-)-gabosine O. The chemical structure and the absolute configuration of (-)-gabosine L are confirmed by its total synthesis.

Total Syntheses of (+)-Gabosine P, (+)-Gabosine Q, (+)-Gabosine E, (-)-Gabosine G, (-)-Gabosine I, (-)-Gabosine K, (+)-Streptol, and (-)-Uvamalol A by a Diversity-Oriented Approach Featuring Tunable Deprotection Manipulation

A new diversity-oriented approach to C7-cyclitols, which possess a broad spectrum of biological activities, is developed. The key polyoxygenated intermediates with different O-protecting groups were accessed by an intramolecular aldol-cyclization of a diketone derived from δ-d-gluconolactone. The versatile intermediates can be easily transformed into structurally different carbasugars based on control of deprotection manipulation. The utility of the robust approach is illustrated by the first syntheses of (+)-gabosines P and Q, as well as the syntheses of several other gabosines and related analogues viz. (+)-gabosine E, (-)-gabosine G, (-)-gabosine I, (-)-gabosine K, (+)-streptol, and (-)-uvamalol A. In addition, the absolute configuration of (-)-uvamalol A is assigned by its total synthesis.

Biosynthesis and Biological Activity of Carbasugars

The first synthesis of carbasugars, compounds in which the ring oxygen of a monosaccharide had been replaced by a methylene moiety, was described in 1966 by Professor G. E. McCasland’s group. Seven years later, the first true natural carbasugar (5a-carba-R-D-galactopyranose) was isolated from a fermentation broth of Streptomyces sp. MA-4145. In the following decades, the chemistry and biology of carbasugars have been extensively studied. Most of these compounds show interesting biological properties, especially enzymatic inhibitory activities, and, in consequence, an important number of analogues have also been prepared in the search for improved biological activities. The aim of this review is to give coverage on the progress made in two important aspects of these compounds: the elucidation of their biosynthesis and the consideration of their biological properties, including the extensively studied carbapyranoses as well as the much less studied carbafuranoses.

Synthesis of chiral hydroxylated enones as potential anti-tumor agents

A series of chiral hydroxylated enones were synthesized as COTC ether analogues to investigate the structural features required for optimal and selective anti-tumor activity. The cytotoxicity of the seven COTC ether analogues against WRL-68 normal and HepG2, HL-60 cancer cell lines were measured. C-4 ether analogues with an aliphatic chain substituent were found to be more favorable than their aromatic counterparts. Inversion of the configuration at C-4 in 5e to give 5f only resulted in reduced selectivity towards cancer cells. These results show that 4-O-pentyl-gabosine D (5e) has optimum selectivity and cytotoxicity towards two cancer cell lines.

Cytotoxic 2-benzylidene-6-(nitrobenzylidene)cyclohexanones which display substantially greater toxicity for neoplasms than non-malignant cells

Various 2-benzylidene-6-(nitrobenzylidene)cyclohexanones were prepared as candidate cytotoxins in which the nitro group was located in the ortho, meta and para positions leading to series 1-3, respectively. The CC(50) values towards human HSC-2 and HSC-4 oral squamous cell carcinomas as well as human HL-60 promyelocytic leukemic cells are in the low micromolar range in general. On the other hand, most of the compounds afforded clear evidence of being far less toxic towards human HGF gingival fibroblasts, HPC pulp cells and HPLF periodontal ligament fibroblasts which are non-malignant cells. Selectivity index (SI) figures were generated which are the ratios of the average CC(50) values towards normal cells and the CC(50) figure towards a malignant cell line. Huge SI values were obtained for many of the compounds. In particular 1c, 2f, 3c and 3g which have average SI values of >76, >38, 124 and 341, respectively, are clearly lead molecules affording direction for amplification of this area of study. A lead compound 1c caused internucleosomal DNA fragmentation and activation of caspase-3 in HL-60 cells but not in HSC-2 carcinomas. In a short-term toxicity study, doses up to and including 300 mg/kg of the majority of the compounds prepared in this study did not cause any mortalities to mice. Some guidelines for development of these tumor-selective cytotoxins are presented.

Glyoxalase-I is a novel target against Bcr-Abl+ leukemic cells acquiring stem-like characteristics in a hypoxic environment

Abl tyrosine kinase inhibitors (TKIs) such as imatinib and dasatinib are ineffective against Bcr-Abl(+) leukemic stem cells. Thus, the identification of novel agents that are effective in eradicating quiescent Bcr-Abl(+) stem cells is needed to cure leukemias caused by Bcr-Abl(+) cells. Human Bcr-Abl(+) cells engrafted in the bone marrow of immunodeficient mice survive under severe hypoxia. We generated two hypoxia-adapted (HA)-Bcr-Abl(+) sublines by selection in long-term hypoxic cultures (1.0% O(2)). Interestingly, HA-Bcr-Abl(+) cells exhibited stem cell-like characteristics, including more cells in a dormant, increase of side population fraction, higher beta-catenin expression, resistance to Abl TKIs, and a higher transplantation efficiency. Compared with the respective parental cells, HA-Bcr-Abl(+) cells had higher levels of protein and higher enzyme activity of glyoxalase-I (Glo-I), an enzyme that detoxifies methylglyoxal, a cytotoxic by-product of glycolysis. In contrast to Abl TKIs, Glo-I inhibitors were much more effective in killing HA-Bcr-Abl(+) cells both in vitro and in vivo. These findings indicate that Glo-I is a novel molecular target for treatment of Bcr-Abl(+) leukemias, and, in particular, Abl TKI-resistant quiescent Bcr-Abl(+) leukemic cells that have acquired stem-like characteristics in the process of adapting to a hypoxic environment.

Carbocyclization of carbohydrates: diastereoselective synthesis of (+)-gabosine F, (-)-gabosine O, and (+)-4-epi-gabosine O

Exploitation of silica gel/chloramine T mediated intramolecular nitrile oxide-alkene cycloaddition (INOC) of sugar-derived oximes to carbocycles furnished the first synthesis of gabosine F from l-arabinose in 12 steps with 23% overall yield, thereby confirming its absolute configuration. Similarly, efficient syntheses of gabosine O and 4-epi-gabosine O were accomplished from D-mannose in 9 and 11 steps with 41% and 38% overall yields, respectively, involving INOC, regioselective dehydration, and diastereoselective hydrogenation as the key steps.

Facile syntheses of (+)-gabosines A, D, and E

(+)-Gabosines A (12), D (4), and E (5), which share the same trihydroxycyclohexenone skeleton, were synthesized from enone 11 as the common intermediate. The key building block 11 was accessed by an intramolecular aldol cyclization of a diketone derived from D-glucose (8).

Glyoxalase I Glu111Ala polymorphism in patients with breast cancer

Effect of advanced glycation end products (AGEs) in the pathogenesis of cancer could be diminished by interaction with soluble RAGE or by reducing AGE-precursors via glyoxalase I. Glu111Ala polymorphism of glyoxalase I gene, AGEs, and sRAGE serum levels were studied in 113 breast cancer patients and in 58 controls. Higher frequency of the mutated C allele was found in patients with negative estrogen receptors and in patients in clinical stage III compared to controls (P< 0.05). The presence of the C allele could represent a negative prognostic factor; however, further studies are needed to confirm this hypothesis.

Short syntheses of gabosine I and gabosine G from delta-D-gluconolactone

A short synthesis of gabosine I (1) from delta-D-gluconolactone (3) in four steps, involving a one-pot TPAP oxidation-K2CO3-mediated intramolecular Horner-Wadsworth-Emmons (HWE) olefination as the key step, is described. Regioselective acetylation of the primary alcohol in gabosine I (1) then furnished gabosine G (2).

Analogues of 2-crotonyloxymethyl-(4R,5R,6R)-4,5,6-trihydroxycyclohex-2-enone (COTC) with anti-tumor properties

The syntheses of three novel analogues of the naturally occurring cytotoxic agent COTC are described and the results of bioassays of the target compounds against two lung cancer cell lines are presented.

A possible regulatory role of 17beta-estradiol and tamoxifen on glyoxalase I and glyoxalase II genes expression in MCF7 and BT20 human breast cancer cells

The glutathione-dependent glyoxalases system, composed of glyoxalase I (GloI) and glyoxalase II (GloII) enzymes, is involved in the detoxification of methylglyoxal, a by-product of cell metabolism. Aberrations in the expression of glyoxalase genes in several human cancers have been reported. Sometimes, these aberrations seem to differ depending on the organs and on the sensitivity of the tumours to estrogens, as we previously detected in the hormone-responsive breast cancer compared to the hormone-independent bladder cancer. To investigate a possible regulatory role of estrogens, as well as antiestrogens, on glyoxalases system, estrogen receptor (ER)-positive MCF7 and ER-negative BT20 human breast cancer cells were cultured in the presence of 17beta-estradiol (E2) and tamoxifen (TAM) performing two independent experiments. After a 24 h or 4 days treatment, we evaluated GloI and GloII mRNA levels, by Ribonuclease Protection Assay (RPA), enzymatic activities spectrophotometrically and cell proliferation by [3H]thymidine incorporation. We found that both steroid molecules affected glyoxalases gene expression and proliferation in a different manner in the cell lines. The modifications in mRNA levels were accompanied by parallel changes in the enzymatic activities. The possibility that modulation of glyoxalase genes by E2 and TAM are due to the presence of estrogen response elements (ERE) or cross-talk mechanisms by proteins of the estrogen signal transduction pathways are discussed. Knowledge regarding the regulation of glyoxalases by E2 and TAM may provide insights into the importance of this enzymes in human breast carcinomas in vivo.

Novel and Efficient Syntheses of (−)-Methyl 4-epi-Shikimate and 4,5-Epoxy-Quinic and -Shikimic Acid Derivatives as Key Precursors to Prepare New Analogues

We have developed simple methods that provide a rapid entry into the synthesis of a series of quinate and shikimate analogues, including (-)-methyl 4-epi-shikimate and the 4,5-epoxy analogues of the parent acids. Epoxy derivatives of quinic and shikimic acids were converted into methyl scyllo-quinate and (+)-methyl 3-epi-shikimate, respectively, by processes involving a regio- and stereoselective epoxide ring opening. The strategies described take place through short, high-yield reaction sequences.