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Synthesis of peptides was an arduous task before development of the solid phase method. The solid phase method has facilitated automated peptide synthesis and the development of combinatorial chemistry. It has many advantages compared with classical solution peptide synthesis, but requires a large amount of organic solvents. Disposal of organic solvents is one of many important environmental problems, therefore we decided to perform peptide synthesis in water. To perform synthesis in water, protected amino acids must be water-soluble. We have studied water-soluble N-protecting groups and we developed 2-[phenyl(methyl)sulfonio]ethoxycarbonyl (Pms) 1,2) as a water-soluble N-protecting group. Since the Pms group is an onium salt, it is rather unstable in comparison with N-protecting groups which are in general use (such as t-butoxycarbonyl group, 3) benzyloxycarbonyl group 4) and 9-fluorenylmethoxycarbonyl (Fmoc) group 5) ) for peptide synthesis. Here we report preparation of the ethanesufonylethoxycarbonyl (Esc) group and its application to peptide synthesis in water.Tesser and Balvert-Geers 6) reported the methanesulfonylethoxycarbonyl (Msc) group as a readily removable Nprotecting group by treatment with 0.1 or 0.2 N NaOH solution. This protecting group is hydrophilic rather than hydrophobic. We designed the Esc group (Fig. 1), expecting it to display both hydrophilic and hydrophobic character (i.e. we expect Esc-amino acids to exhibit reasonable solubility in aqueous and organic solvents). The Esc group was introduced onto amino acids by the reaction of 2-ethanesulfonylethyl chloroformate (Esc-Cl) as shown in Chart 1 (Route 1). 2-Ethanesulfonylethanol was converted to Esc-Cl by treatment with phosgene (prepared from triphosgene) 7) in dichloromethane. Since Esc-Cl was labile and decomposed during purification, it was used without purification for the next acylating reaction. Esc-Cl, H-Phe-OH and triethylamine were allowed to react in aqueous 50% acetonitrile to give Esc-Phe-OH. HPLC analysis of the crude product exhibited impurities and the product could not be purified by silica gel column chromatography and recrystallization. Pure Esc-Phe-OH was obtained by RP-HPLC purification and the yield was 38%. To improve the reaction yield and purification procedure, another synthetic route (Route 2 in Chart 1) to the Escamino acid was studied. 2-Ethanesulfonylethanol was reacted with 4-nitrophenyl chloroformate to give ethanesulfonylethyl-4-nitrophenyl carbonate (Esc-ONp). The crude EscONp was stable and could be purified by silica gel column chromatography or recrystallization from a mixture of ether and hexane. The yield was 78%. Other Esc-amino acids (Esc-Leu-OH, Esc-Gly-OH, Esc-Tyr-OH) were also prepared using Esc-ONp and their analytical data are shown in Table 1. Esc-Gly-OH and Esc-Tyr-OH were soluble in water and Esc-Leu-OH and Esc-Phe-OH were not readily soluble in water. Esc-Leu-OH and Esc-Phe-OH were soluble in aqueous 2% Triton X. To evaluate Esc-amino acids, Leu-enkephalin amide was synthesized by the sol...

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SUMMARY The non-invasive 133Xe inhalation method was modified to measure regional cerebral blood flow (rCBF) of both hemispheres and brain stem-cerebellar (BSC) regions in baboons to serve as a model for clarifying and validating human studies. Measurements were made in the alert, unanesthetized state at rest and during activation with spontaneous respiration in a primate chair or during sedation or anesthesia with mechanical respiration for direct comparison with the intra-arterial