Rotational conformation synthesis

Beckmann rearrangement, 4, 292 phototransposition, 4, 204 synthesis, 4, 223 Wittig reaetion, 4, 294 Wolff-Kishner reduetion, 4, 291 Pyrrole, 1-aeyl-barrier to rotation, 4, 193 IR speetra, 4, 21, 181 rearrangement, 4, 41 synthesis, 4, 82 thermal rearrangement, 4, 202 Pyrrole, 2-aeyl-aeidity, 4, 297 cleavage, 4, 289 conformation, 4, 33... 

Pyrrole, 4-ethynyl-2-formyl-3-methyl-synthesis, 4, 222 Pyrrole, formyl-oxidation, 4, 289 reactions, 4, 292 with sulfoxides, 4, 293 synthesis, 4, 223, 274, 287 Pyrrole, 1-formyl-barrier to rotation, 4, 193 Pyrrole, 2-formyl-benzoylation, 4, 220 conformation, 2, 107 4, 193 diacetoxythallium derivative iodination, 4, 216 dipole moment, 4, 194 ketals, 4, 290 protonation, 4, 47 reactions... 

Thiirane, 2-phenyl-conformation rotational barriers, 7, 138 polymerization, 7, 144 Thiirane, tetraaryl-synthesis, 7, 175 Thiirane, tetrafluoro-halogenation, 7, 148 polymerization, 7, 144 reactions... 

The synthesis of key intermediate 6 begins with the asymmetric synthesis of the lactol subunit, intermediate 8 (see Scheme 3). Alkylation of the sodium enolate derived from carboximide 21 with allyl iodide furnishes intermediate 26 as a crystalline solid in 82 % yield and in >99 % diastereomeric purity after recrystallization. Guided by transition state allylic strain conformational control elements5d (see Scheme 4), the action of sodium bis(trimethylsilyl)amide on 21 affords chelated (Z)-enolate 25. Chelation of the type illustrated in 25 prevents rotation about the nitrogen-carbon bond and renders... 

The catalytic cycle can be divided into three phases, through each of which the three active sites pass in sequence. First, ADP and Pj are bound (1), then the anhydride bond forms (2), and finally the product is released (3). Each time protons pass through the Fo channel protein into the matrix, all three active sites change from their current state to the next. It has been shown that the energy for proton transport is initially converted into a rotation of the y subunit, which in turn cyclically alters the conformation of the a and p subunits, which are stationary relative to the Fo part, and thereby drives ATP synthesis. 

Another result of great importance—the conformational asymmetric polymerization of triphenylmethyl methacrylate realized in Osaka (223, 364, 365)— has already been discussed in Sect. IV-C. The polymerization was carried out in the presence of the complex butyllithium-sparteine or butyllithium-6-ben-zylsparteine. The use of benzylsparteine as cocatalyst leads to a completely soluble low molecular weight polymer with optical activity [a]o around 340° its structure was ascertained by conversion into (optically inactive) isotactic poly(methyl methacrylate). To the best of my knowledge this is the first example of an asymmetric synthesis in which the chirality of the product derives finom hindered rotation around carbon-carbon single bonds. 

ATP synthesis takes place by conformational changes at the catalytic binding sites. Recent structural [21, 27], biochemical [13, 28, 31], spectroscopic [32, 33] and microscopic [34, 35] studies indicate that these conformational changes arise from rotation of the y- subunit in a static barrel of agPj subunits in ATP synthase, making it the world s smallest molecular machine with a rotor radius of 1 nm (Fig. 1). 

Energy transmitted over the drive shaft induces the release of newly synthesized ATP on one of the /3-subunits, simultaneously promotes ATP synthesis on the next /3-subunit and coneomitantly binds ADP, Mg + and Pi to the third . It is suspected that ADP is bound before Pj . A binding-change mechanism is often used to illustrate this rotational behavior. One of the three /3-subunits is believed to be in an open O conformation. Upon rotation, this changes to a loose L conformation with a high binding affinity for ADP and Pj. After these substrates are bound, rotation results in a tightly closed conformation T in which ATP is synthesized. Further rotation opens the conformation (now O) and ATP is released . Upon a rotation of 360°, each /3-subunit has successively bound ADP and Pi, synthesized ATP and released it. 

Recently, studies of the conformation of oligomers were extended to peptides derived from /3-methyl-L-aspartates. Their synthesis (n = 2 up to 14) was described by Goodman and Boardman (82), and later the specific rotations of their solutions in dimethyl formamide, dichloro-acetic acid and in chloroform were determined (83). The oligomers exist in a random-coil form in the first two solvents, but helices become stable in chloroform for n — 11 and 14. These peptides are unusual since their L-amino-acid residues produce a left-hand helix (84, 85) whereas most of the investigated polyamino acids crystallise as a right-hand helix (86). 

---