Synthesis of sphinganine analogues modified in the head group

Preparation of indium nitronates and their Henry reactions

Indium nitronates were readily prepared from commercially available nitroalkanes by transmetallation of the corresponding lithium nitronates with indium salts. The Henry reaction of this indium organometallics with aldehydes afforded β-nitroalkanols in moderate to high yields. The use of chiral sugar aldehydes furnished the corresponding carbohydrate-derived β-nitroalkanols with excellent stereoselectivity.

Novel amide- and sulfonamide-based aromatic ethanolamines: effects of various substituents on the inhibition of acid and neutral ceramidases

In the present study we describe the design and synthesis of a series of amide- and sulfonamide-based compounds as inhibitor of recombinant acid and neutral ceramidases. Inhibition of ceramidases has been shown to induce apoptosis and to increase the efficacy of conventional chemotherapy in several cancer models. B-13, lead in vitro inhibitor of acid ceramidase has been recently shown to be virtually inactive towards lysosomal acid ceramidase in living cells at lower concentrations and for a shorter time of treatment, suggesting the development of more potent inhibitors. In this study, a detailed SAR investigation has been performed to understand the effect of different substituents on the phenyl ring of amide- and sulfonamide-based compounds that partially resemble the structure of well-known inhibitors such as B-13, D-e-MAPP as well as NOE. Our results suggest that the electronic effects of the substituents on phenyl ring in B-13 and D-e-MAPP analogues have negligible effects either in enhancing the inhibition potencies or for selectivity towards aCDase over nCDase. However, the hydrophobicity and the steric effects of longer alkyl chains (n-Pr, n-Bu or t-Bu groups) at the phenyl ring were found to be important for an enhanced selectivity towards aCDase over nCDase.

Chemical tools to investigate sphingolipid metabolism and functions

Sphingolipids comprise an important group of biomolecules, some of which have been shown to play important roles in the regulation of many cell functions. From a structural standpoint, they all share a long 2-amino-1,3-diol chain, which can be either saturated (sphinganine), hydroxylated at C4 (phytosphingosine), or unsaturated at C4 (sphingosine) as in most mammalian cells. N-acylation of sphingosine leads to ceramide, a key intermediate in sphingolipid metabolism that can be enzymatically modified at the C1-OH position to other biologically important sphingolipids, such as sphingomyelin or glycosphingolipids. In addition, both ceramide and sphingosine can be phosphorylated at C1-OH to give ceramide-1-phosphate and sphingosine-1-phosphate, respectively. To better understand the biological and biophysical roles of sphingolipids, many efforts have been made to design synthetic analogues as chemical tools able to unravel their structure-activity relationships, and to alter their cellular levels. This last approach has been thoroughly studied by the development of specific inhibitors of some key enzymes that play an important role in biosynthesis or metabolism of these intriguing lipids. With the above premises in mind, the aim of this review is to collect, in a systematic way, the recent efforts described in the literature leading to the development of new chemical entities specifically designed to achieve the above goals.

Short and efficient synthesis of (2S,3R,4R,5R) and (2S,3R,4R,5S)-tetrahydroxyazepanes via the Henry reaction

The Henry reaction with the easily available alpha-d-xylo-pentodialdose afforded a diastereomeric mixture of nitroaldoses with the alpha-d-gluco- and beta-l-ido-configuration, respectively, in good yield. When n-BuLi was used as the base, the reaction afforded the alpha-d-gluco-nitroaldose as the only product. The reduction of the nitro group in the alpha-d-gluco- and beta-l-ido-nitroaldoses, removal of the protecting groups and intramolecular reductive cyclo-amination afforded the corresponding (2S,3R,4R,5R) and (2S,3R,4R,5S) tetrahydroxyazepanes.

Transformation of D-glucose into 1D-3-deoxy-3-hydroxymethyl-myo-inositol by stereocontrolled intramolecular Henry reaction

[reaction: see text] An intramolecular Henry cyclization provides a promising new strategy for the transformation of nitroheptofuranoses into deoxyhydroxymethylinositols. This method has allowed a stereospecific transformation of d-glucose into 1D-3-deoxy-3-hydroxymethyl-myo-inositol.

The identification of myriocin-binding proteins

BACKGROUND

Myriocin is a natural product that potently induces apoptosis of a murine cytotoxic T lymphocyte cell line (CTLL-2) and inhibits a serine palmitoyltransferase (SPT) activity that has been detected in cell extracts and is thought to initiate sphingolipid biosynthesis. Because SPT has never been biochemically purified and a comprehensive appraisal of myriocin-binding proteins has not been conducted, we isolated specific targets using myriocin-based affinity chromatography.

RESULTS

Myriocin derivatives were synthesized and evaluated using CTLL-2 proliferation and SPT activity assays. Guided by these results, affinity chromatography matrices were prepared and two specific myriocin-binding proteins were isolated from CTLL-2 lysates. Analyses of these polypeptides establish conclusively that they are murine LCB1 and LCB2, mammalian homologs of two yeast proteins that have been genetically linked to sphingolipid biosynthesis.

CONCLUSION

The ability of myriocin-containing matrices to bind factors that have SPT activity and the exclusive isolation of LCB1 and LCB2 as myriocin-binding proteins demonstrates that the two proteins are directly responsible for SPT activity and that myriocin acts directly upon these polypeptides.

Induction of apoptosis by synthetic ceramide analogues in the human keratinocyte cell line HaCaT

In contrast to extracellular, long chain ceramides which comprise a structural component of the epidermal water barrier, intracellular ceramides originating from sphingomyelin hydrolysis have been shown to inhibit proliferation and to induce apoptosis in different cell populations. To further elucidate the possible role of intracellular ceramides in human epidermis, two new cell-permeable ceramide analogues, N-thioacetylsphingosine (C2-Cer=S) and 4-dodecanoylamino-decan-5-ol (FS-5), were synthesized and tested for their ability to suppress cell growth and to induce apoptosis in immortalized human keratinocytes. It was shown that the well-investigated ceramide analogue N-acetylsphingosine (C2-Cer=O), as well as the new compound C2-Cer=S inhibited proliferation of HaCaT cells with half-inhibitory concentrations (IC50) of 20 microg/ml and 10 microg/ml, respectively, whereas FS-5 has been potent with an IC50>40 microg/ml. Overall, all three ceramide analogues induced apoptosis in HaCaT cells as assessed by DNA-fragmentation using ELISA technique and in situ nick end labelling, thereby confirming the importance of ceramide signalling in keratinocytes.

Bcl-2 antagonizes apoptotic cell death induced by two new ceramide analogues

Ceramides which arise in part from the breakdown of sphingomyelin comprise a class of antiproliferative lipids and have been implicated in the regulation of programmed cell death better known as apoptosis. In the present study, two new synthetic ceramide analogues, N-thioacetylsphingosine and FS-5, were used in Molt 4 cells to induce cell death. Besides their cytotoxic effects at concentrations > or = 14 microM the data obtained clearly show that both analogues induced apoptosis at concentrations below this critical concentration as assessed by trypan blue exclusion and cleavage of the death substrate poly-(ADP-ribose) polymerase (PARP). Additional experiments in bcl-2-transfected Molt 4 cells revealed that the apoptotic but not the lytic effects of the analogues were antagonized by the apoptosis inhibitor Bcl-2. Furthermore, neither N-thio-acetylsphingosine nor FS-5 induced PARP cleavage in bcl-2-transfected Molt 4 cells indicating that the induction of apoptotic cell death by cell permeable ceramides is not due to unspecific disturbance of the cell membrane.

Potent immunosuppressants, 2-alkyl-2-aminopropane-1,3-diols

Several immunosuppressants, ISP-I [(2S,3R,4R)-(E)-2-amino-3,4-dihydroxy-2-(hydroxymethyl)-14-oxoeicos++ +-6-enoic acid, myriocin = thermozymocidin] and mycestericins A-G, were isolated from culture broths of Isaria sinclairii and Mycelia sterilia, respectively. In order to investigate structure-activity relationships, extensive modifications of ISP-I were conducted, and it was established that the fundamental structure possessing the immunosuppressive activity is a symmetrical 2-alkyl-2-aminopropane-1,3-diol. The tetradecyl, pentadecyl, and hexadecyl derivatives prolonged rat skin allograft survival in the combination of LEW donor and F344 recipient and were more effective than cyclosporin A. Among them, 2-amino-2-tetradecylpropane-1,3-diol hydrochloride, ISP-I-55, showed the lowest toxicity. ISP-I-55 is a promising lead compound for the development of effective immunosuppressants for organ transplantations and for the treatment of autoimmune diseases.