Asymmetric synthesis of chloroisothreonine derivatives via syn-stereoselective Mannich-type additions across N-sulfinyl-α-chloroimines.

Mannich-type reactions of O-Boc glycolic esters across chiral N-sulfinyl-α-chloroaldimines resulted in the efficient and syn-stereoselective synthesis of new γ-chloro-α-hydroxy-ß-amino esters (dr > 99 : 1). The α-coordinating ability of the chlorine atom was of great importance for the diastereoselectivity of the Mannich-type reaction and overruled the chelation of the sulfinyl oxygen with the lithium ion of the incoming E-enolate in the transition state model. These novel chloroisothreonine derivatives proved to be excellent building blocks in asymmetric synthesis of novel syn-ß,γ-aziridino-α-hydroxy esters and biologically relevant trans-oxazolidinone carboxylic esters.

Asymmetric synthesis of γ-chloro-α,ß-diamino- and ß,γ-aziridino-α-aminoacylpyrrolidines and -piperidines via stereoselective Mannich-type additions of N-(diphenylmethylene)glycinamides across α-chloro-N-sulfinylimines.

The asymmetric synthesis of new chiral γ-chloro-α,ß-diaminocarboxylamide derivatives by highly diastereoselective Mannich-type reactions of N-(diphenylmethylene)glycinamides across chiral α-chloro-N-p-toluenesulfinylaldimines was developed. The resulting (S(S),2S,3S)-γ-chloro-α,ß-diaminocarboxylamides were formed with the opposite enantiotopic face selectivity as compared to the (S(S),2R,3R)-γ-chloro-α,ß-diaminocarboxyl esters obtained via Mannich-type addition of analogous N-(diphenylmethylene)glycine esters across a chiral α-chloro-N-p-toluenesulfinylaldimine. Selective deprotection under different acidic reaction conditions and ring closure of the γ-chloro-α,ß-diaminocarboxylamides was optimized, which resulted in N(α)-deprotected syn-γ-chloro-α,ß-diaminocarboxylamides, N-sulfinyl-ß,γ-aziridino-α-aminocarboxylamide derivatives, a trans-imidazolidine, and an N(α),N(ß)-deprotected syn-γ-chloro-α,ß-diaminocarboxylamide.

Asymmetric synthesis of α,ß-diamino acid derivatives with an aziridine-, azetidine- and γ-lactone-skeleton via Mannich-type additions across α-chloro-N-sulfinylimines.

The efficient asymmetric synthesis of new chiral γ-chloro-α,ß-diamino acid derivatives via highly diastereoselective Mannich-type reactions of N-(diphenylmethylene) glycine esters across a chiral α-chloro-N-p-toluenesulfinylimine was developed. The influence of the base, LDA or LiHMDS, used for the formation of the glycine enolates, was of great importance for the anti-/syn-diastereoselectivity of the Mannich-type reaction. The γ-chloro-α,ß-diamino acid derivatives proved to be excellent building blocks for ring closure towards optically pure anti- and syn-ß,γ-aziridino-α-amino esters, and subsequent ring transformation into trans-3-aminoazetidine-2-carboxylic acid derivatives and α,ß-diamino-γ-butyrolactones.

Absorption, translocation and metabolism of metamitron in Chenopodium album.

BACKGROUND: In recent years, common lambsquarters (Chenopodium album L.) populations from sugar beet fields in different European countries have responded as resistant to the as-triazinone metamitron. The populations have been found to have the same D1 point mutation as known for atrazine-resistant biotypes (Ser264 to Gly). However, pot experiments revealed that metamitron resistance is not as clear-cut as observed with triazine resistance in the past. The objectives of this study were to clarify the absorption, translocation and metabolic fate of metamitron in C. album. RESULTS: Root absorption and foliar absorption experiments showed minor differences in absorption, translocation and metabolism of metamitron between the susceptible and resistant C. album populations. A rapid metabolism in the C. album populations was observed when metamitron was absorbed by the roots. The primary products of metamitron metabolism were identified as deamino-metamitron and metamitron-N-glucoside. PABA, known to inhibit the deamination of metribuzin, did not alter the metabolism of metamitron, and nor did the cytochrome P450 inhibitor PBO. However, inhibition of metamitron metabolism in the presence of the cytochrome P450 inhibitor ABT was demonstrated. CONCLUSION: Metamitron metabolism in C. album may act as a basic tolerance mechanism, which can be important in circumstances favouring this degradation pathway.