Solid racemization

The crude sodium threo-(+/-)-(E)-3,5-dihydroxy-7-[3 -(4"-fluorophenyl)-l -(l"-methylethyl )indol-2 -yl]hept-6-enoate is dissolved in water, and the solution is acidified to pH 2 with 2 N hydrochloric acid and extracted with diethyl ether. The diethyl ether extract is washed three times with saturated sodium chloride solution, dried over anhydrous magnesium sulfate and evaporated at reduced pressure to obtain the crude solid racemic erythro-(+/-)-(E)-3,5-dihydroxy-7-[3 -(4"-fluorophenyl)-l,-(l"-methylethyl )indol-2 -yl] hept-6-enoic acid (6.9 g). 

A solution of a solid racemic substance under suitable conditions may deposit individual crystals each of which is composed chiefly or exclusively of one or the other of the two active components. The crystalline deposit as a whole contains equal weights of the two active components and is commonly known as a racemic mixture or conglomerate The... 

Form Supplied in white solid racemic and optically active BNPPA are commercially available. 

The IR spectrum of the solid racemate is the same as that of the single enantiomer... 

Constit. of Microcyte multiflorus and Nematolepis phebalioides. Amorph. solid. Racemic. 

The N-to-C assembly of the peptide chain is unfavorable for the chemical synthesis of peptides on solid supports. This strategy can be dismissed already for the single reason that repeated activation of the carboxyl ends on the growing peptide chain would lead to a much higher percentage of racemization. Several other more practical disadvantages also tend to disfavor this approach, and acid activation on the polymer support is usually only used in one-step fragment condensations (p. 241). 

The major disadvantage of solid-phase peptide synthesis is the fact that ail the by-products attached to the resin can only be removed at the final stages of synthesis. Another problem is the relatively low local concentration of peptide which can be obtained on the polymer, and this limits the turnover of all other educts. Preparation of large quantities (> 1 g) is therefore difficult. Thirdly, the racemization-safe methods for acid activation, e.g. with azides, are too mild (= slow) for solid-phase synthesis. For these reasons the convenient Menifield procedures are quite generally used for syntheses of small peptides, whereas for larger polypeptides many research groups adhere to classic solution methods and purification after each condensation step (F.M. Finn, 1976). 

Vitamin K compounds ate yellow solids or viscous liquids. The natural form of vitamin is a single diastereoisomer with 2 (E), 7 (R), ll (R) stereochemistry. The predominant commercial form of vitamin is the racemate and a 2 (E)j (Z) mixture. Table 1 fists some physical and spectral properties of vitamin K. ... 

Camphor was originally obtained from the camphor tree Lauras eamphora in which it appeared in the optically active dextro-rotary form. Since about 1920 the racemic ( ) mixture derived from oil of turpentine has been more generally used. By fractional distillation of oil of turpentine the product pinene is obtained. By treating this with hydrochloric acid, pinene hydrochloride (also known as bomyl chloride) may be produced. This is then boiled with acetic acid to hydrolyse the material to the racemic bomeol, which on oxidation yields camphor. Camphor is a white crystalline solid (m.p. 175°C) with the structure shown in Figure 22.3. 

The relative stereostructure of 9-acetyl-7-hydroxy-l,2-dimethyl-7-meth-oxycarbonyl-4-phenyl-6-oxo-l, 4,7,8-tetrahydro-6/7-pyrido[l, 2-u]pyri-midine-3-carboxylate 122 was justified by an X-ray diffraction analysis (97JOC3109). The stereochemistry and solid state structure of racemic trans-6,9-//-l, 6-dimethyl-9 z-ethoxy-9-hydroxy-4-oxo-l,6,7,8,9,9 z-hexahydro-4//-pyrido[l,2- z]pyrimidine-3-carboxylate (123), adopting a cw-fused conformation, were determined by X-ray investigations (97H(45)2175). 

The following is taken from U.S. Patent 3,061,517. Sixteen grams of racemic 3-(2-pYridyl)-3-p-bromophenyl-N,N,-dimethylpropylamine and 9,7 grams of d-phenylsuccinic acid are dissolved in 150 ml of absolute alcohol and kept at room temperature until crystallization is effected. The crystals are filtered, washed with absolute ethyl alcohol, and recrystallized from the same solvent using 5 ml thereof per gram of solid. Three subsequent crystallizations from 80% alcohol give d-3-(2-pYridYl)-3-p-bromophenYl-N,N-dimethylpropYlamine-d-phenylsuccinate MP 152°-154°C 91 (concentration, 1% in dimethylformamide). 

Then, as described in U.S. Patent 3,158,648, the optical isomers may be resolved as follows. 37 g of racemic a-methYl-3,4-dihYdroxYphenylalanine are slurried at 35°C in 100 cc of 1.0 N hydrochloric acid. The excess solids are filtered leaving a saturated solution containing 34.6 g of racemic amino acid of which about 61% is present as the hydrochloride. The solution Is then seeded at 35°C with 7 g of hydrated L-o -methYl-3,4-dihYdroxYphenYlalanine (6.2 g of anhydrous material). The mixture is then cooled to 20°C in 30 minutes and aged one hour at 20°C. The separated material Is isolated by filtration, washed twice with 10 cc of cold water and dried in vacuo. The yield of product is 14.1 g of L-a-methYl-3,4-di-hydroxyphenylalanine in the form of a sesquihydrate of 100% purity as determined by the rotation of the copper complex. 

A mixture of 50 parts by weight of racemic 2-acetylamino-1 -(4-methylmercaptophenyl)-1,3-propanediol, 100 parts by weight of concentrated hydrochloric acid, and 500 parts by weight of water was warmed on a steam bath for thirty minutes. The resulting solution was cooled to about 40 C and was then made strongly alkaline by addition of 35% aqueous sodium hydroxide solution. The alkaline solution was then refrigerated. The white solid which separated from the cooled solution was collected on a filter. There was thus obtained 27 parts by weight of 2-amino-1-(4-methylmercaptophenyl)-1,3-propanediol. This product melted at 130.7°C to 131 after recrystallization from methanol. 

First, they compared CSPs 1 and 3 prepared by the two-step solid-phase methodology with their commercially available counterparts (CSPs 2 and 4) obtained by direct reaction of the preformed selector with a silica support. Although no exact data characterizing the surface coverage density for these phases were reported, all of the CSPs separated all four racemates tested equally. These results shown in Table 3-3 subsequently led to the preparation of a series of dipeptide and tripeptide CSPs 5-10 using a similar synthetic approach. Although the majority of these phases exhibited selectivities lower or similar to those of selectors built around a single amino acid (Table 3-3), this study demonstrated that the solid-phase synthesis was a... 

Our strategy consisted of the following steps A mixture of potential chiral selectors is immobilized on a solid support and packed to afford a complete-library column , which is tested in the resolution of targeted racemic compounds. If some separation is achieved, the column should be deconvoluted to identify the selector possessing the highest selectivity. The deconvolution consisted in the stepwise preparation of a series of sublibrary columns of lower diversity, each of which constitute a CSP with a reduced number of library members. 

Plouvier then prepared the previously unknown racemic form of proto-quercitol by mixing equal weights of the two enantiomers. The melting point (237°C.) of the mixture was not depressed, and its (presumably solid state) infrared spectrum reportedly (36) was identical with that of either active form. It thus appears that DL-proto-quercitol exists as a solid solution, not a racemic compound or conglomerate. 

A solution of racemic 3-(2-ethylhexyIoxy)phthaIonitriIe (5 2 g, 7.8 mmol) in 2-(dimcthylainino)cthanol was heated with NiCl2 (0.26 g, 2 mmol) for 24 h at 140 C. The solvent was distilled off under vacuum and the product was purified several times by column chromatography (silica gel, toluene/hexane 7 3). A dark-blue solid was obtained yield 0.22 g (10%). 

Another example of reagent-induced asymmetric synthesis is the enantioselective preparation of phosphoramides 6 by addition of dialkylzine reagents to A-diphenylphosphinoylimincs 4 in the presence of the enantiomerically pure 1,2-amino alcohols 5a or 5 b (diethylzinc does not add to A-silyl- or A-phenylimines)12. Phosphoramides 6 (crystalline solids) are obtained in moderate to good yield and good enantioselectivity. The latter can be enhanced by recrystallization. Acidic hydrolysis with dilute 3 M hydrochloric acid/tetrahydrofuran provides the corresponding amines 7 without any racemization. 

Mechanisms in the racemization of optically active coordination complexes in the solid state. P. O Brien, Polyhedron, 1983, 2,233-243 (54). 

Cobalt, aquachlorobis(l, 2-ethanediamine)-racemization solid state, 1,467 Cobalt, aquahalotctraammine-di halide... 

Cobalt, tris(l,2-ethanediamine)-conformation, 1,25,197 polarography, 1,481 racemization, 1, 466 solid state, 1,466,467 reactions, 1, 27 redox potential, 1, 514 structure, 1, 67... 

Cobalt, tris(oxalato)-racemization solid state, 1, 467 structure, 1, 68... 

Iron, tris(hexafluoroacetylacetone)-structure, 1,65 Iron, tris(oxalato)-chemical actinometer, 1,409 photoreduction, 1,471 relief-image-forming systems, 6,125 Iron, tris(l,10-phenanthroline)-absorptiometry, 1,549 racemization, 1,466 solid state, 1,467 structure, 1, 64 lron(III) chloride amino acid formation prebiotic systems, 6,871 Iron complexes acetonitrile. 4,1210 acetylacetone, 2,371 amidines... 

Nickel, tris(l, 10-phenanthroline) racemization, 1,24. 466 solid state, 1, 467 structure, 1,64 Nickel complexes, 5,1-300 acetylacetone alcoholysis, 2, 380 pyridine complexes, 2, 386 solvolysis, 2,379 structure, 2,388 amidines... 

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