Synthesis of arsinolipids. II. A non-isosteric analogue of fully acylated cardiolipin

Trithioarsenites [(RS)3As], dithioarsonites [R-As(SR′)2] and thioarsinites [R2As-SR′]: Preparations, chemical, biochemical and biological properties

Contrary to P(V) compounds, As(V) compounds can very easily reduced by thiols to As(III) thiolates that are deemed to play a central role in the metabolism of arsenic and therefore a review on the preparation and properties of the title thiolates can be of interest. The preparation of trithioarsenites, dithioarsonites and thioarsinites involves reactions of a thiol with a proper As(V) or As(III) precursor via 4-centered transition states or a thiolate by SN2 mechanisms. Convenient precursors are the solids As2O3, arsonic and arsinic acids, although for the latter two acids the separation of the product from the co-produced disulfides can be problematic. Only a few crystal structures have been reported and involve only trithioarsenites. From their chemical properties, the hydrolyses, transthiolations and air oxidations are of particular interest from mechanistic and biochemical/biological points of view. Their nucleophilicity towards alkyl halides and acyl derivatives revealed unexpected behavior. Although these molecules have many free electron pairs only three reports were found pertaining to their reaction with metal cations (Hg2+) and metal carbonyls; the mercuric complexes being not characterized. Only a few studies appeared for the action of the title compounds towards enzymes, while the patent literature revealed that they have bactericidal, fungicidal and insecticidal activities for agricultural applications, some have antiparasitic activity on animals and a few are carcinostatic.

Preparation of dl-2,3,4-trihydroxybutylarsonic acid and dl-2,3-dihydroxybutane-1,4-bis(arsonic acid): starting compounds for novel arsonolipids

The reaction of DL-1,3-butadiene diepoxide and of DL-1,4-dibromo-2,3-butanediol with aqueous alkaline sodium arsenite, "Na(3)AsO(3)", gave mixtures of the title arsonic acids which can be separated by anion exchange resin. Characterization of by-products leads to a better understanding of these reactions. These compounds are valuable intermediates for the preparation of novel arsonic acids and bis(arsonic acids).

Arsenolipids

Natural arsenolipids are analogues of neutral lipids, like monoglycerides, glycolipids, phospho- and also phosphonolipids. They have been found in microorganisms, fungi, plants, lichens, in marine mollusks, sponges, other invertebrates, and in fish tissues. This review presented structures of natural arsenolipids (and derivatives), their distribution, biogenesis in algae and invertebrates, synthesis, and also biological activity. Arsenolipids are thought to be end products of arsenate detoxification processes, involving reduction and oxidative methylation and adenosylation. The proposed biogenesis of arsenolipids is based on the natural occurrence of arsenic metabolites, and all the intermediates in the proposed pathway have been identified as natural products of algal origin. Different arseno species are shown to be inhibitors of glycerol kinase, bovine carbonic anhydrase, and also is an effective therapy for acute promyelocytic leukemia, and there has been promising activity noted in other hematologic and solid tumors. Arsonoliposomes demonstrated high anti-trypanosomal activity against Trypanosoma brucei and inhibit growth of some types of cancer cells (HL-60,C6 and GH3).

The reaction of allyl and benzylarsonic acids with thiols: mechanistic aspects and implications for dioxygen activation by trivalent arsenic compounds

The reaction of allyl and benzylarsonic acids with thiophenol gives not only the expected diphenyl alkyldithioarsonites and diphenyl disulfide but also various other compounds arising from the decomposition at the arsenic(V) oxidation level (the arsonic acids) by thiophenol and at the arsenic(III) oxidation level (mainly the alkyldithioarsonites) by thiophenol and by dissolved dioxygen. The reaction of these arsonic acids with 4-nitrothiophenol, which is not oxidized by dioxygen, revealed that the arsenic(III) of these alkyldithioarsonites is the active atom towards dioxygen. However, the reaction of allyl, benzyl, and 2-picolylarsonic acids with DL-penicillamine gives the expected products with no or very small oxidative decomposition. The decomposition pathways of allyl and benzylarsonic acids were elucidated. The results are briefly discussed in the contexts of the use of arsonic acids in chemotherapy and the ability of arsenic(III) compounds to generate reactive oxygen species.

Preparation of pseudo-arsonolipids: 2-acyloxypropane-1,3-bis(arsonic acids). The crystal structure of 2-hydroxypropane-1,3-bis(arsonic acid)

Epihalohydrins react with alkaline arsenite to give in very good yields 2-hydroxypropane-1,3-bis(arsonic acid) (7), a key compound for the synthesis of pseudo-arsonolipids and more complex arsinolipids. Through a series of reduction to -As(SPh)(2), acylation, and oxidation to -AsO(3)H(2), pseudo-arsonolipids, i.e. 2-acyloxypropane-1,3-bis(arsonic acids), were obtained. These pseudo-lipids are very sensitive to bases, being de-acylated. The bis(arsonic acid) (7) crystallizes in the orthorombic space group P2(1)2(1)2(1) with unit cell constants a=6.911(3), b=17.496(8), c=7.002(3) A. Both arsenic atoms are essentially tetrahedral being bound to three oxygens and one carbon. All hydrogen atoms have been located. There is no intramolecular but only intermolecular hydrogen bonding involving all the As=O, As-OH, and C-OH groups. The C-OH group acts as a hydrogen donor to an acidic As-OH, and this As-OH, in turn, acts as a hydrogen donor to an As=O group.