Novel routes to 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines and 5,6,9,10,11,11a-hexahydro-8H-pyrido[1,2-a]pyrrolo[2,1-c]pyrazines

Condensation reactions of benzotriazole and 2-(pyrrol-1-yl)-1-ethylamine (1) with formaldehyde and glutaric dialdehyde, respectively, afforded intermediates 2 and 6. Subsequent nucleophilic substitutions of the benzotriazole group in 2 and 6 with Grignard reagents, sodium cyanide, and sodium borohydride gave 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazines 3a-e, 4, 5 and 5,6,9,10,11,11a-hexahydro-8H-pyrido[1,2-a]pyrrolo[2,1-c]pyrazines 7a-c, 8, 9, respectively, in good yields.     

Novel Syntheses of N-Pivot Lariat Diaza-Crown Ethers from 4,13-Bis(benzotriazolylmethyl)-4,13-diaza-1,7,10,16-tetraoxacyclooctadecane

4,13-Bis(benzotriazolylmethyl)-4,13-diaza-1,7,10,16-tetraoxacyclooctadecane (6) was synthesized as a versatile intermediate in the preparation of bis(lariats) of diaza-18-crown-6. N,N'-Bis(umbelliferon-8-ylmethyl) derivative 8, bis(lariats) with terminal unsaturated groups (11c,e), ester functionalities (11d), N,N'-di-beta-aralkyl derivatives (11a,b), and gamma-oxy-substituted (13, 14) and gamma-amino-substituted (17-19) propylene-side-armed derivatives were thus prepared in moderate to excellent yields. The X-ray structure of bis(lariat) 6 and stability constants for several of the complexes of bis(lariats), derivatives of 6, with metal cations are discussed.     

Synthesis of 3,4-dihydro-2H-1,3,5-thiadiazines

3,4-Dihydro-2H-1,3,5-thiadiazines substituted at the 3 and 6 positions were synthesized by treatment of N-substituted N,N-bis(1H-1,2,3-benzotriazol-1-ylmethyl)-amines with thioamides and zinc bromide in dry CH(2)Cl(2) at room temperature for 48-60 h in 48-80% yields.     

A general method for the preparation of perfluoroalkanesulfonyl chlorides

A mild two-step synthesis of perfluoroalkanesulfonyl chlorides starting from perfluoroalkyl iodides has been developed. Reaction of perfluoroalkyl iodides with sodium dithionite gave sodium perfluoroalkanesulfinate salts which were converted into perfluoroalkanesulfonyl chlorides in 25-73% yield (two steps) using N-chlorosuccinimide.     

Conformational dynamics of the isoalloxazine in substrate-free p-hydroxybenzoate hydroxylase: single-molecule studies

p-Hydroxybenzoate hydroxylase (PHBH) is a homodimeric enzyme in which each subunit noncovalently binds one molecule of FAD in the active site. PHBH is a model system for how flavoenzymes regulate reactions with oxygen. We report single-molecule fluorescence studies of PHBH in the absence of substrate that provide data consistent with the hypothesis that a critical step in substrate binding is the movement of the isoalloxazine between an "in" conformation and a more exposed or "open" conformation. The isoalloxazine is observed to move between these conformations in the absence of substrate. Studies with the Y222A mutant form of PHBH suggest that the exposed conformation is fluorescent while the in-conformation is quenched. Finally, we note that many of the single-molecule-fluorescence trajectories reveal a conformational heterogeneity, with populations of the enzyme characterized by either fast or slow switching between the in- and open-conformations. Our data also allow us to hypothesize a model in which one flavin in the dimer inhibits the motion of the other.     

Highly diastereoselective reactions of (E)-cinnamyl chloride with aldehydes mediated by tin and aluminium

The reactions of (E)-cinnamyl chloride with aldehydes in H₂O: THF: HBr in the presence of tin and aluminium powders proceed with very high stereoselectivity.     

An investigation of the conformational dynamics of ion-pair intermediates in the syn-elimination of 8a-methyldecahydronaphthalen-4a-ols

The (4aβ,8aβ)-8a-methyl(5β D)decahydronaphthalen-4a-ol has been prepared and its reaction with H₂SO₄-Ac₂O-HOAc shown to occur with a k_h/k_D of 2.2 (±0.2) by loss of a proton (deuteron) syn to the departing oxy-anion. The results are used as a probe of carbocation-anion conformational mobility.