Trifluoroacetic acid recoveries after

The solid-state reaction was also conducted for Cgo with alkyl or aryl bromides (RBr) in the presence of alkali metals (M) in the molar ratio of 1 2-3 4-6 under the HSVM conditions for 30 min. After the reaction mixture was treated with trifluoroacetic acid, the main product was isolated and identified as the alkyl or aryl derivative of l,2-dihydro-C6o 41, obtained in the rather modest yield of 6-24% with 13-49% recovery of C q (Scheme 18) [50]. 

Determinative and confirmatory methods of analysis for PIR residue in bovine milk and liver have been developed, based on HPLC-TS-MS (209). Milk sample preparation consisted of precipitating the milk proteins with acidified MeCN followed by partitioning with a mixture of -butylchloride and hexane, LLE of PIR from aqueous phase into methylene chloride, and SPE cleanup. The dry residue after methylene chloride extraction was dissolved in ammonium hydroxide, and this basic solution was transferred to the top of Cl8 SPE column. The PIR elution was accomplished with TEA in MeOH. For liver, the samples were extracted with trifluoroacetic acid (TFA) in MeCN. The aqueous component was released from the organic solvent with n-butyl chloride. The aqueous solution was reduced in volume by evaporation, basified with ammonium hydroxide, and then extracted with methylene chloride. The organic solvent was evaporated to dryness, and the residue was dissolved in ammonium acetate. The overall recovery of PIR in milk was 94.5%, RSD of 8.7%, for liver 97.6%, RSD of 5.1 %. A chromatographically resolved stereoisomer of PIR with TS-MS response characteristics identical to PIR was used as an internal standard for the quantitative analysis of the ratio of peak areas of PIR and internal standard in the pro-tonated molecular-ion chromatogram at m/z 411.2. The mass spectrometer was set for an 8 min SIM-MS acquisition. Six samples can be processed and analyzed in approximately 3 hours. 

During a synthesis of the Chlorothricolide, Roush and Sciotti encountered unexpected problems with the hydrolysis of the dimethyl acetal 54.1 [Scheme 2.54].112 Use of some of the standard hydrolysis conditions (oxalic acid, PPTS, PTSA, HO Ac, or trifluoroacetic acid — all in acetone) resulted in recovery of 54.1 or decomposition. Success was achieved by exploiting the mild Lewis acidic properties of the lithium cation under conditions first reported by Lipshutz and Harvey.113 Thus treatment of the dimethyl acetal 54,1 with lithium tetrafluoroborate in acetonitrile containing 2% water returned the desired aldehyde 54J in 97% yield after 2 h at room temperature. The reaction was also applied to the deprotection of a cyclic ketal in a synthesis of Pumi-liotoxin.114 115... 

Chemistry for the Automated C-Terminal Sequence Analysis of Proline Containing Polypeptides. Application of the acetic anhydride/TMS-ITC/TFA procedure, used for the synthesis of TH-proline, to the tripeptide, N-acetyl-Ala-Phe-Pro, in our laboratory, found that thiohydantoin proline was formed in low yield (approx. 1-2% of theoretical). Recovery of the peptide products after the reaction revealed that approximately half of the starting peptide was unchanged and the remaining hdf had been decarboxylated at the C-terminus, thereby blocking it to C-terminal sequence analysis. This was most likely caused by the high concentration of trifluoroacetic acid, the excess of acetic anhydride present, and the high temperature (80°C) at which the reaction was performed. 

The polymer was prepared similarly to the first example from a mixture of ethylene dimethacrylate (4.67 g), methyl methacrylate (0.22 g), A, A -diethyl-4-vinylbenzamidine (10a) (0.442 g 2.188 mmol) template 14 (0.350 g 1.094 mmol), AIBN (56.8 mg), and tetrahydrofuran (5.64 mL) as the porogen. Polymerization in a sealed ampoule was carried out for 70 h at 60 °C. After the usual workup procedure, the template was removed from the particles by extraction with methanol, followed by washing twice with 0.1 m NaOH/acetonitrile (1 1), water, and acetonitrile. The recovery of the template from the washings was determined by HPLC [RP8-column, eluent 0.2% trifluoroacetic acid in water/acetonitrile (55 45)]. Recovery of template was 85%. The inner surface area of the polymer amounted to 228 m g, and the swelling ratio in methanol was 1.45. 

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