Early procedures

Transition-Metal Catalyzed Cyclizations. o-Halogenated anilines and anilides can serve as indole precursors in a group of reactions which are typically cataly2ed by transition metals. Several catalysts have been developed which convert o-haloanilines or anilides to indoles by reaction with acetylenes. An early procedure involved coupling to a copper acetyUde with o-iodoaniline. A more versatile procedure involves palladium catalysis of the reaction of an o-bromo- or o-trifluoromethylsulfonyloxyanihde with a triaLkylstaimylalkyne. The reaction is conducted in two stages, first with a Pd(0) and then a Pd(II) catalyst (29). 

Gaseous SO2 is an example. Very early procedures detected the presence of SO2 in ambient air by exposing a lead peroxide candle for a period of time and then measuring the amount of lead sulfate formed. Because the volume of air in contact with the candle was not measured, the technique could not quantify the amount of SO2 per unit volume of air. 

Subsequently, several laboratories developed improvements in the early procedures. It was first recommended that the reaction be carried out at a low temperature ca. —T) for better results. A more notable improvement is the use of dimethylformamide-t-butanol as the solvent system, a temperature range of —20 to —25°, and the presence of triethyl phosphite during the reaction to reduce the hydroperoxide as it is formed. The triethyl phosphate which is produced is water soluble and overall yields are generally in the range of 60-70 %. 

Both L-gulose12,13 (9) and D-gulose (d-9, see Ref. 10) have been oxidized with bromine to L- or D-gulonic acid, respectively (see Scheme 1). L-Gulose (9) has been prepared by a number of different procedures. Schemes 2 and 3 show two early procedures that afforded L-gu-lose, but the overall yields were low (<30%). In the first procedure12 (see Scheme 2), D-glucitol (10) was converted into 2,4-O-benzylidene-D-glucitol (11), which was then oxidized with lead tetraacetate to 2,4-O-benzylidene-L-xylose (12). Nitromethane was added to 12 to afford crystalline 13 in 50% yield. Hydrolysis of 13 provided 14, which was treated with sodium hydroxide, followed by sulfuric acid, to afford 9, which was isolated in 52% yield as the 2-benzyl-2-phenylhydrazone. 

Early procedures used stoichiometric amounts of the quaternary ammonium catalyst to solubilize the preformed sodium or potassium salts of the active methylene compounds (prepared under anhydrous conditions) in the organic medium. Subsequently, liquidrliquid two-phase procedures using catalytic amounts of the quaternary ammonium salts were developed, and solidrliquid two-phase conditions have been used to improve yields. In some cases, only the solidrliquid two-phase procedures are effective. 

Bierenstiel and Schlaf [22] were able to prepare and isolate for the first time the less stable 8-D-galactonolactone by oxidation of galactose with the Schvo s catalytic system, which is based on the dimeric ruthenium complex [(C4Pli4CO)(CO)2Ru]2. The transformation led to the 5-galactonolactone in 93% yield, against 7% of the isolated y-lactone isomer. This procedure also allowed the preparation of 5-D-man-nonolactone in a much better yield (94%) than that reported in an early procedure [23] based on crystallization from a solution of calcium mannonate in aqueous oxahc acid. 

While substantially all early procedures were developed for binary mixtures, preliminary steps were being made to apply them to multicomponent mixtures. The concept... 

Differential Solubility Methods. Numerous methods have been developed to obtain one or more of the various caseins from whole casein or directly from skim milk based on their differential solubility (Thompson 1971 Mackinlay and Wake 1971 Whitney 1977). While some early procedures indicated the possibility of fractionating whole casein into different components, it was not until the 1950s that systematic procedures were proposed for the fractionation of casein into Warner s a-, 0-, and y-caseins. Hipp et al. (1952) developed two procedures which have been used extensively or partially incorporated into other methods. The first is based upon the differential solubilities of the caseins in 50% alcohol in the presence of ammonium acetate by varying the pH, temperature, and ionic strength. The second procedure involves the dispersion of whole casein in 6.6 M urea and the separa-... 

The majority of the early procedures for the cleavage of the (3-lactams /Vj-CT bond deal with hydrolysis and alcoholysis processes under rather harsh acid or basic reaction conditions. One example is the ring opening of (3-lactam 2 under acidic conditions to afford almost quantitative (3-amino ester 3, a component of the dimeric cyclic depsipeptide onchidin, 1, isolated from the marine mollusc Onchi-dium sp., Scheme 1 [54]. 

An early procedure used triethyl phosphate directly on the diketone, but better yields are obtained by the oxidation of the corresponding dihydrazone 42 The oxidant may be mercury(n) oxide, which is rather expensive 43 alternatively copper(i) chloride in dichloromethane and pyridine is oxidised with oxygen gas, and the derived complex is then used to oxidise the dihydrazone to the acetylenic group with the evolution of nitrogen.44 The reaction is illustrated by the conversion of benzil dihydrazone into diphenylacetylene (Expt 5.25). 

One of the earliest syntheses of (11) involved condensation of a-bromo-/ ,/ -diethoxypropanal with 2,4,5-triamino-6-hydroxypyrimidine followed by oxidation of the resulting 5,6-dihydropterin (13) and hydrolysis of the acetal [37]. This early procedure is clearly equivocal, however, since the initial condensation reaction is known to lead to a mixture of regioisomers. The first... 

Finally, two other practical points are worth mentioning. The early procedures for asymmetric epoxidation called for dilute solutions of sodium hydroxide to effect tartrate ester hydrolysis. For the reasons given 1n Note 11, one should always (unless one is certain that the epo y alcohol 1s completely Insoluble in water) use Instead NaOH 1n brine. In this procedure, the excess tert-butyl hydroperoxide (TBHP) was destroyed early in the work-up (FeSC ), although this is not essential because dilute solutions of TBHP are... 

This is the best reaction for the preparation of ortho esters. The imino ester hydrochlorides are available in excellent yields by partial alcoholysis of nitriles (method 402). In early procedures, the hydrochlorides and excess alcohol were allowed to stand at room temperature for 5 to 40 days. The time of reaction can be reduced to 6 to 28 hours by carrying out the alcoholysis in refluxing ether solution. Good yields are common for both steps in the process. The principal side reaction is the thermal... 

The reaction of benzaldehyde with phenylacetic acid to produce a mixture of the a-carboxylic acid derivatives of Z- and -stilbene a form of aldol condensation known as the Perkin reaction, is effected by heating a mixture of the components with acetic anhydride and triethylamine. In the course of the reaction the phenylacetic acid is probably present both as anion and as the mixed anhydride resulting from equilibration with acetic anhydride. A reflux period of 5 h specified in an early procedure has been shortened by a factor of 10 by restriction of the amount of the volatile acetic anhydride, use of an excess of the less expensive, high-boiling aldehyde component, and use of a condenser that permits some evaporation and consequent elevation of the reflux temperature. 

Procedure 3 papain, leucine aminopeptidase, prolidase This early procedure for enzymic hydrolysis of proteins was reported by Hill and Schmidt (1962) to be successful for hydrolysis of several proteins. Papain was found to be superior to subtilisin or a combination of trypsin and chymotrypsin for the initial hydrolysis. The method might be improved if aminopeptidase M (discovered after the method was developed) is used in place of the leucine aminopeptidase, but to our knowledge this has not been tested. The problem with diketo-piperazine formation from X-Pro dipeptides in aminopeptidase M hydrolysates of peptides (see above) may make this substitution less desirable than it would seem at first. 

Numerous purification procedures have been described (for a review on early procedures see78,149). Most authors use chromatographical methods. The most efficient procedures include adsorption chromatography on brushite as the first step as described in detail by Rice et al.141). Because adsorption of phytochrome on brushite columns sometimes fails63,144) other adsorbents like hydroxylapatite were used... 

This reaction is usually called the Wolff-Kishner reduction.14 In early procedures, sodium ethoxide was the base commonly employed and the reaction was carried out at about 180° in a sealed tube. A simplified technique, however, has been developed for carrying out the reaction in diethylene glycol solution with sodium o potassium hydroxide Little i lmown concerning the mechanism of the reaction, but two possibilities 14(16 are shown on p. 275. 

Preparation. An early procedure involving distillation of acetone through a combustion tube packed with broken pieces of porous porcelain and heated in a... 

Lead oxide is used in an early procedure for the conversion of an amino acid hydrochloride into the free amine. A solution of alanine hydrochloride in water is... 

An early procedure which alfords a quick if inefficient route to toluquinone consists in steam distillation of a mixture of o-toluidine, manganese dioxide, and sulfuric acid. The reagent has been used to oxidize pyridoxine (1) to pyridoxal 2f and to oxidize pyridoxamine phosphate (3) to pyridoxal phosphate (4). ... 

Trihydrate. Mol. wt. 136.09. Use of the reagent for neutralization of a reaction mixture or liberation of a reagent from a salt (hydrazine sulfate ) requires no comment. Where anhydrous reagent is required, that now available commercially is entirely satisfactory (early procedures often called for use of material that had been freshly fused and powdered). 

Preparation, An early procedure involved cooling a solution of sodium methoxide in methanol to —5°, adding a cold solution of dibenzoyl peroxide in chloroform,... 

Dehalogenation, dehydrohalogenation. An early procedure for debromination of 5a,6/8-dibromocholestane-3-one without isomerization of the nonconjugated ketone initially formed involved reaction with zinc dust in hot ethanol, but the reaction proceeds better in ether containing a catalytic amount of acetic acid (see above ). 

There are several methods available for the extraction of bile salts from serum or plasma. The most convenient methods utilize some form of liquid-solid extraction. An early procedure involved the anion-exchange resin, Amberlyst A-26 (S8), but considerable time and effort was required to perform column chromatography and to concentrate the eluate from the column. The introduction in 1972 of the neutral resin, Amberlite XAD-2, improved the ease of extracting bile acids and their conjugates from serum samples (M6). Further improvement occurred in 1977 with the description of a batch extraction technique using the related neutral resin, Amberlite XAD-7 (B5). With this technique, serum is diluted in 0.1 M sodium hydroxide to release bile acids from albumin and mixed with resin for 1 hour. After washing the resin in dilute alkali, bile acids are eluted with methanol, which cdn be removed on a rotary evaporator (B5). 

Modification of the protein amine groups is the procedure most frequently used to produce antibody-liposome conjugates. Early procedures used crosslinking agents, such as l-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) (27,28) in the presence of preformed liposomes containing a lipophilic carboxylic acid. Condensing agents like these tend to form protein-protein polymers. Control of these reactions is typically difficult and complex, and as a result separation of the liposomes from protein polymers is a... 

As noted (1, 132), an early procedure of Eliel and Doyle for the reduction of 4-t-butylcyclohexanone to cis-4-f-butylcyclohexanol used iridium trichloride supplied by Fisher. This reagent is no longer available and, in a newer procedure,1 iridium tetrachloride is used as catalyst in combination with trimethyl phosphite, which undergoes hydrolysis to phosphorous acid the actual reducing agent is probably... 

Preparation. The reagent is prepared by the reaction of excess sodium azide in water-ethanol with benzenesulfonyl chloride. In an early procedure the latter reagent was dissolved in ethanol before addition to the sodium azide solution.1 In a more recent preparation, benzenesulfonyl chloride is added directly to the ethanolic solution of sodium azide.2... 

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