Stanislav A. Amelichev

Direct synthesis of fused 1,2,3,4,5-pentathiepins

Treatment of nucleophilic heterocycles like pyrroles and thiophenes, and their tetrahydro derivatives, with S2Cl2 and DABCO in chloroform at room temperature provides a simple one-pot synthesis of fused mono and bispentathiepins. N-Methylpyrrole and its 2-chloro and 2,5-dichloro derivatives and N-methylpyrrolidine all give the same dichloropentathiepin 1a. N-Ethyl, isopropyl and tert-butylpyrrolidine behave similarly; the isopropylpyrrolidine also gives the bispentathiepin 6which undergoes an intriguing rearrangement to the symmetrical monopentathiepin 1c. N-Methyl and ethyl indole give either 2,3-dichloro derivatives 8 or the pentathiepinoindoles 9, depending upon the reaction conditions. Thiophene and tetrahydrothiophene give the pentathiepin 10. X-Ray crystal structures are provided for the pentathiepins 1a and 1d, and possible reaction pathways are suggested for the extensive cascade reactions reported.

1,2,3-Dithiazoles – new reversible melanin synthesis inhibitors: a chemical genomics study

A chemical genomic screen of an in-house library of small molecule heterocycles was carried out using Xenopus laevis embryos. This led to the identification of N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-4-methoxyaniline (1c), which elicits loss of pigmentation in melanophores and the retinal pigment epithelium (RPE) of developing embryos, independent of the developmental stage of initial exposure. The phenotype was reversible, since pigmentation returned upon compound removal while analysis of neural crest cell markers (Pax7) and melanophore markers (Dct/Xtrp2) revealed that both neural crest precursors and fully differentiated melanophores were present in the dithiazole 1c treated embryos. A subsequent focused structure–activity relationship (SAR) study identified the more active dithiazole 4-benzyloxy-N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-aniline (1l) and the need for a chlorine substituent at the dithiazole C-4 position. Both the initial chemical genomic screen and the focused SAR study highlighted the toxicity of (dithiazolylidene)aminoazines, and also of methoxyaniline (anisidine) analogues that hosted strong electron-withdrawing or electronegative substituents or acidic hydroxyl groups on the anisidine moiety. This study suggests that 1,2,3-dithiazoles can act as reversible melanin synthesis inhibitors, revealing a new biological activity for this class of compounds. The inhibition of melanin synthesis is medically relevant as a potential treatment for pigmentation disorders such as melasma.

Regioselective synthesis of pentathiepines fused with pyrrole, thiophene, or indole rings

Pentathiepines fused with pyrrole, thiophene, or indole rings were obtained by reactions of the corresponding heterocycles or their tetrahydro derivatives with a prepared mixture of sulfur monochloride and DABCO.

Synthesis of bis[1,2]dithiolo[1,4]thiazine imines from Hünig's base

N-Ethyldiisopropylamine, S2Cl2 and DABCO in chloroform at room temperature form intermediate salts which react with nucleophiles to give tricyclic bis[1,2]dithiolo[1,4]thiazine derivatives. The reactions of some representative amino compounds as the nucleophiles are now described. With arenesulfonamides 1a,b and their N,N-dichloro derivatives 2a,b, the N,N′-bis(arylsulfonyl)dithiolothiazinediimines 3a,b are formed in modest yields. With toluene-p-sulfonohydrazide and aniline the more complex reactions give only the monohydrazone 7 and the bicyclic anilino derivative 8, respectively, in very low yields. The diimines 3a,b are also produced, in better yield, from the bis(1,2-dithiole-3-thione) 4 with chloramine B and T; similarly the analogous monothione 12 gives the monoimines 13a,b. The reaction rates and yields (up to 93%) in the conversion of 12 to 13 are greatly increased by scandium triflate. Possible reaction mechanisms are considered.

Synthesis of 1,2,5,6-tetrathiocines from fused 1,2,3,4,5-pentathiepines

Abstract1,2,3,4,5-Pentathiepines fused with the pyrrole, thiophene, and indole systems react with sodium cyanide in acetonitrile to form the corresponding tri-and pentacyclic fused 1,2,5,6-tetrathiocines. In the case of unsymmetric pentathiepines annulated at the b side of thiophene or indole, mixtures of isomeric tetrathiocines (∼1: 1) are formed.