H2S signals via protein persulfidation. To be regulatory the modification will have to be reversible. Using a new method for persulfide detection, we discover this missing link and show that thioredoxin system acts as depersulfidase in vivo.

Spontaneous symmetry breaking in reactive systems, known as a rare physical phenomenon and for the Soai autocatalytic irreversible reaction, might in principle also occur in other, more common asymmetric reactions when the chiral product is capable to promote its formation and an element of "nonlinearity" is involved in the reaction scheme. Such phenomena are long sought after in chemistry as a possible explanation for the biological homochirality of biomolecules. We have investigated homogeneous organic stereoselective Mannich and Aldol reactions, in which the product is capable to form H-bridged complexes with the prochiral educt, and found by applying NMR spectroscopy, HPLC analysis, and optical rotation measurements 0.3-50.8% of random product enantiomeric excess under essentially achiral reaction conditions. These findings imply a hitherto overlooked mechanism for spontaneous symmetry breaking and, hence, a novel approach to the problem of absolute asymmetric synthesis and could have also potential significance for the conundrum of homochirality.

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A new and effective organocatalytic system: primary amine derived chiral thiourea catalyst and AcOH-H2O additive, which converts different ketones to gamma-nitroketones in high yields (82-99%) and enantioselectivities (90-99%) has been described.

Dedicated to Professor Lutz F. Tietze on the occasion of his 65th birthdayAsymmetric autocatalysis is the process of automultiplication of a chiral compound in which the chiral product acts as a chiral catalyst for its own formation.[1] Such reactions offer striking advantages as the chiral product does not need to be separated from the chiral catalyst and as no other chiral catalyst than the product itself is involved. Several examples are known, all of which involve organometallic reagents and are hence restricted to certain reaction types; [1][2][3] the most prominent of these is the Soai reaction for its ability to amplify a tiny initial enantiomeric excess of a chiral pyrimidyl alkanol in the presence of iPr 2 Zn to almost enantiomeric purity.[3c] A catalytic asymmetric autoinductive aldol reaction in the presence of Ti IV (binol) complexes was described by Szlosek and Figadre. [4] Whereas a purely organic specimen of product catalysis is known, such as the autocatalytic aldol reaction, [5] asymmetric examples of such reactions have not yet been reported.However, Sievers and von Kiedrowski described a template-based mechanism of autocatalytic self-replication of (naturally asymmetric) oligonucleotide strands.[6] Moreover, Bolm and co-workers cited a fully organocatalytic example of enantioselective autoinduction in the production of a chiral cyanhydrine, catalyzed by a cyclic dipeptide. The product and the external catalyst together form here a more efficient catalytic species, which resulted in higher ee values and yields. [7] These results led us to pose the question of whether the product alone could in principle act as an inductor of chirality and in any asymmetric organic reaction. Reversible reactions appear to be badly suited for such an undertaking, as racemization might occur by the reverse reaction. Additionally, if the reaction-accelerating feature of the product is poorly developed, competition with the "uncatalyzed" reaction further limits the achievable enantiomeric excesses.Herein, we demonstrate for the first time that even in quite ordinary (and reversible) asymmetric organic reactions (as opposed to reactions involving organometallic species) the chiral product alone could act as a catalyst with high stereoselectivity. As an example, we chose the asymmetric Mannich reaction [8] [Eq. (1)] under various reaction conditions. The choice fell on an example that allows for specific product-substrate interactions through hydrogen-bonded complexes of the product molecules with the prochiral substrate.First, we prepared the product catalyst with l-proline as external catalyst in 98 % ee (S) and with d-proline in 99 % ee (R) enantiomeric purity. [8,9] Experiments carried out under various conditions (different concentrations of educt; different solvents; different ee values, absolute configuration, and loadings of catalyst; variable temperatures and reaction times; see Table 1) revealed to our surprise that the product is formed in nearly the same enantiomeric purity as that of the initially added pr...