Dithiolane ring

Dithiolane (132) derivatives also possess non-planar skeletons the most important conformation is probably of symmetry C2 (half-chair). The dithiolane ring may be quite flexible and a minimum energy. conformation is only well defined if there is a bulky substituent at the 2-position. 

An acyl-transfer and redox coenzyme containing two sulfhydryl groups that form a dithiolane ring in the oxidized (disulfide) form. The redox potential at pH 7 is -0.29 volts. Lipoic acid is attached to the e-amino group of lysyl residues of transacetylases (subunit of a-ketoacid dehydrogenase complexes), thereby permitting acyl... 

Disulfide rearrangements in proteins, PROTELN DLSULFLDE LSOMERASE Dithiolane ring formation,... 

Expansion of the dithiolane ring is involved in the stereoselective formation of 2-azido-l,4-dithianes (Scheme 43) <99T801> and of the spiro-linked dithiane 61 <99CC1673>. 

The 1,3 -dithiolane ring also can be cleaved by alkylative hydrolysis using different reagents (77S357). For example treatment of the 1,3-dithiolane derivative (220) with triethyloxonium tetrafluoroborate followed by hydrolysis with copper(II) sulfate solution and basification gives the ketone (221) in 95% yield (77S357). 

The preparation of the 1,3-dithiolane ring system (279) can be carried out by reaction of a carbonyl compound with ethanedithiol in the presence of either boron trifluoride etherate in methanol or p-toluenesulfonic acid monohydrate in acetic acid (74S32). 

Diisopropyl phosphonodithioformates 597 were also found to be efficient C=S dipolarophiles in reaction with thiocarbonyl ly-methylides, affording spiro-substituted 1,3-dithiolanes 598-601 with the phosphonate moiety at the 1,3-dithiolane ring (Scheme 85) <2005EJ01604>. 

This section deals with the synthesis of 1,3-dithiole and 1,3-dithiolane rings. No investigations on ring synthesis of 1,3-dithiolium ions and mesoionic 1,3-dithiole derivatives were reported in this category. 

The chemistry of the 1,2-dithioles and related compounds was covered in the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I), and a review, published in 1990, of some systems containing the 1,2-dithiolane ring <90SR257>. Reviews of other 1,2-dithioles were published in the early 1980s <80SRi, 82AHC(3i)63>. Since 1985 there has been a marked increase in published applications of 1,2-dithioles. 

In rats the metabolism of mephospholan (102) is characterised by hydroxylation of the methyl group of the dithiolan ring, as well as by cleavage of the P—N bond (Zulalian and Blinn, 1977) as shown is Scheme 1.15. 

Dithiolane ring The five-membered ring generated upon intramolecular disulfide-bond formation in lipoic acid. 

This compound is the product of oxidation of the enamine by any one of the following oxidizing agents on enzymes most commonly by the dithiolane ring of lipoic acid covalently amidated to a lysine side chain in the 2-oxoacid dehydrogenase multienzyme complexes less frequently by FAD in the pyruvate oxidases — these come in two flavors, forming acetate in Escherichia coli and forming acetylphosphate in L. plantarum, finally by NAD. ... 

The various intermediates in lipoate (157) catabolism have been identified in pseudomonads that were grown on lipoate (157) as the sole source of carbon and sulfur " (Figure 17). These degraded products have also been detected in the rat. Bisnorlipoate (158), tetranorlipoate (160), and /3-hydroxybisnorlipoate (159) are the result of /3-oxidation of the valeric side chain of lipoate (157). " In addition, the dithiolane ring undergoes oxidation to thiolsulfmates (161-163). No enzymes or genes associated with these transformations have yet been identified. 

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