l-Proline catalyzed efficient and convenient synthesis of substituted 2H-chromenes by three-component reaction

A convenient and efficient method is described for the synthesis of alkoxy substituted 2H-chromens by l-proline catalyzed reaction of salicylaldehydes with diketone in alcohol. The method is applicable for various substituted salicylaldehydes and aliphatic as well as benzylic alcohols.     

Synthesis of chiral thiourea–phosphine organocatalysts derived from l-proline

A novel class of thiourea–phosphine was prepared from l-proline as a chiral renewable resource. The original structure of the chiral framework offers an interesting potential to the construction of bifunctional organocatalysts for asymmetric transformations.     

l-Proline catalyzed one-step synthesis of 4,5-diaryl-2H-1,2,3-triazoles from heteroaryl cyanostilbenes via [3+2]cycloaddition of azide

Use of a novel reagent has been established for the synthesis of a series of 4,5-diaryl-2H-1,2,3-triazoles (6a–i and 9a–e) from cyanostilbene analogs of benzo[b]thiophene, benzo[b]furan, and indole, catalyzed by l-proline via Lewis base-catalyzed one-step [3+2]cycloaddition of azide. This method provides an efficient, simple, and environmentally benign procedure that affords good yields and relatively short reaction times.     

Pd(PPh3)4-catalyzed direct ortho-fluorination of 2-arylbenzothiazoles with an electrophilic fluoride N-fluorobenzenesulfonimide (NFSI)

An efficient protocol was developed for regio-selective Pd-catalyzed direct ortho-fluorination of 2-arylbenzo[d]thiazoles using N-fluorobenzenesulfonimide (NFSI) as the F⁺ source, and l-proline as the crucial promoter. The present method offered a practical route to synthesize valuable fluorinated products, which are of potential importance in the pharmaceutical and agrochemical industries.     

l-Proline induced self-assembly of indolicidin derived palindromic tripeptide

We describe the synthesis, crystal structure, and various microscopic studies of the palindromic tripeptide WPW derived from antimicrobial peptide indolicidin. The present study reveals that tripeptide 1 and 2 undergo self-assembly to form vesicular structures after prolonged incubation, thus giving an interesting insight into the contribution of l-proline and flanking tryptophan residues in the self-assembly process. These vesicles were also amenable to simple focused ion beam (FIB)-aided bisection and thus possible to mill these vesicles to create different shapes. The circular dichroism (CD) analysis indicates that incubation promotes and stabilizes the more favorable secondary structures for 1 and 2. Preliminary result shows that tripeptide 1 exhibits appreciable interaction with Tb³⁺ as determined by quenching in tryptophan fluorescence.     

l-Proline catalyzed expeditious multicomponent protocol for the synthesis of fused N-substituted-2-pyridone derivatives in aqueous medium

N-substituted-2-pyridone derivatives have many pharmaceutical properties. In our research, we have developed an efficient, green, and multicomponent protocol to synthesize such new fused N-substituted-2-pyridone derivatives. Optimum reaction condition was obtained by employing l-proline as an organocatalyst in aqueous SDS solution at 100 °C. Various 1,3-diketones, including indane 1,3-dione with a range of aromatic and aliphatic amines were utilized to synthesize fused 2-pyridone derivatives. The isolation of a reaction intermediate confirmed our proposed mechanism. Water as a reaction medium improved the scope of the reaction methodology to a large extent.     

l-Proline-catalyzed three-component domino reactions for the synthesis of highly functionalized pyrazolo[3,4-b]pyridines

A series of novel N,3-dimethyl-5-nitro-1-aryl-1H-pyrazolo[3,4-b]pyridin-6-amines was obtained in good yields from the domino reactions of N-methyl-1-(methylthio)-2-nitroprop-1-en-1-amine, aromatic aldehydes, and 3-methyl-1-aryl-1H-pyrazol-5-amines in ethanol in the presence of green catalyst, l-proline. This transformation involves the formation of two C–C and one C–N bonds leading to the creation of a six-membered ring in a one-pot operation.     

Synthesis, spectral characterization and biological studies of some organotin(IV) complexes of L-proline, trans-hydroxy-L-proline and L-glutamine

New organotin(IV) complexes of the general formula R3Sn(L) (where R=Me, n-Bu and HL=L-proline; R=Me, Ph and HL=trans-hydroxy-L-proline and L-glutamine) and R2Sn(L)2 (where R=n-Bu, Ph and HL=L-proline; R=Ph, HL=trans-hydroxy-L-proline) have been synthesized by the reaction of RnSnCl(4-n) (where n=2 or 3) with sodium salt of the amino acid (HL). n-Bu2Sn(Pro)2 was synthesized by the reaction of n-Bu2SnO with L-proline under azeotropic removal of water. The bonding and coordination behavior in these complexes have been discussed on the basis of IR and 119Sn M?ssbauer spectroscopic studies in the solid-state. Their coordination behavior in solution has been discussed with the help of multinuclear (1H, 13C and 119Sn) NMR spectral studies. The 119Sn M?ssbauer and IR studies indicate that L-proline and trans-hydroxy-L-proline show similar coordination behavior towards organotin(IV) compounds. Pentacoordinate trigonal-bipyramidal and hexacoordinate octahedral structures, respectively, have been proposed for the tri- and diorganotin(IV) complexes of L-proline and trans-hydroxy-L-proline, in which the carboxylate group acts as bidentate group. L-glutamine shows different coordination behavior towards organotin(IV) compounds, it acts as monoanionic bidentate ligand coordinating through carboxylate and amino group. The triorganotin(IV) complexes of L-glutamine have been proposed to have trigonal-bipyramidal environment around tin. The newly synthesized complexes have been tested for their antiinflammatory and cardiovascular activities. Their LD50 values are >1000 mg kg-1.