conditions as above) showed the signals of 27b (tR = 7.53 min), acetone (tR = 4.55 min), and acetic anhydride (tR = 15.93 min), as confirmed by injection of authentic samples.Reduction of 29 with Triphenylphosphine at -30 °C. A solution of 44 mg (0.188 mmol) of 29 (mixture of racemic and meso) in 70 ph of CDC13 was admixed with 79 mg (0.30 mmol) of triphenylphosphine at -30 °C and left at this temperature. 1H NMR analysis (CDC13, Me4Si) of samples after 13 and 36 h showed the presence of 27b ( 2.33, s), 30 (S 2.29, s),18 acetone ( 2.17, s), and acetic anhydride ( 2.23, s) in molar ratios of 20:9:49:1 and 31:5:65:1, respectively.Thermal Decomposition of 29 in Dichloromethane. (a) Isolation of 38 and 39. A solution of 1.2 g (5.1 mmol) of 29 (mixture of racemic and meso) in 10 mL of dichloromethane was heated to 50 °C for 40 h, and the solvent was removed at room temperature and 15 Torr. The liquid residue was dissolved in 30 mL of diethyl ether and washed with aqueous sodium bicarbonate, and the ether was removed at room temperature and 15 Torr to leave 1.88 g of a residue. It was separated by column chromatography (silica gel, pentane/diethyl ether, 4:1) to give 240 mg of 39 and a fraction containing impure 38. The latter was purified by preparative GLC (glass column, 0.7 X 400 cm, 5% Carbowax 20 M on Chromosorb G; 130 °C for 15 min, 130-180 °C at 16 °C/min).2,3-Dimethyl-l,3-dioxolan-4-one (38): 1H NMR (CDC13,

addition funnel, and nitrogen inlet were placed 38.7 g (0.29 mol) of aluminum chloride and 150 ml of methylene chloride. After the gas flow was established, monochloramine was added below the surface during 1 hr at 10-15°. After an additional 30 min, a 10-ml sample was removed. Uv analysis24 indicated no chlorine and a trace of trichloramine present. The remaining mixture was hydrolyzed with 50 ml of hydrochloric acid and 50 ml of water for 5 min at 30°. Uv analysis of a 10-ml sample showed the presence of chlorine, but no trichloramine. Uv analysis of the first sample after 24 hr showed a larger amount of trichloramine.

The method developed by Edmun[*l for the sequential analysis of peptidesin which the N-terminal amino acid of a protein is made t o react with phenyl isothiocyanate, cleaved off as 5-thiazolinone, and subsequently detected after rearrangement to the thiohydantoin derivativehas been modified in many ways. All variants of the degradation, however, suffer from a common failing: Incompletely degraded portions of peptide are present in the next degradation cycle; hence, from step to step in the degradation reaction there appear more and more thiohydantoins so that after a few cycles it becomes more difficult and finally impossible to identify the main product of degradation. This is particularly true in the case of monotonous peptide sequences.We have now found that the use of 4-isothiocyanatobenzenesulfonic acid, as suggested by Just [21, affords a simple means of identifying the degradation products of a peptide sequence. The sulfonated phenylthiocarbamoyl peptide ( I ) occurring in this Edman degradation can be separated quite easily from unreacted peptides by ionexchange chromatography o n DEAE Sephadex (CI-form, diameter 1.5 cm, length 20 cm) using 0.1 N HCI as eluent. On evaporating the acid eluate the N-terminal amino acid derivative is cleaved from the peptide and immediately rearranges t o the 4-sulfophenylthiohydantoin (2). The peptide, which is now shorter by one amino acid is separated from the cleaved amino acid derivative by further chromatography on the DEAE Sephadex column before carrying out the next degradation step. The compound (2) eluted from the column can be unequivocally identified as the pure substance by thin-layer chromatography using an authentic sample for comparison.We tested the 'new variant of the degradation on the tripeptide Phe-Ala-Val which we had treated according t o the procedure given by Edman[ll. The peptide (2 mmole, 670.8 mg) was dissolved in pyridine/water (1:l; 25 rnl); the p H of the solution was adjusted to 8.7 by addition of 1 N NaOH. The addition of sodium 4-isothiocyanatobenzenesulfonate (4 mmoles, 950 mg) dissolved in pyridinelwater (1:l) was carried out at this p H and 40°C. Reaction was complete after 25 minutes. The reaction mixture was then extracted twice with benzene and the aqueous phase neutralized and evaporated at 3 0°C under vacuum. The resulting residue was dissolved in water and transferred t o the above mentioned DEAE Sephadex column; this was eluted with 0.1 N HCI. The unreacted peptide (

The evidence (CD, X-ray) strongly implies that the dimethyltrien-Co-aminomethylmalonate complex (3) contains the N-0 bound malonate moiety exclusively in the R configuration. This signifies that the dimethyltrien-Co moiety coordinates one carboxylate group to the complete exclusion of the other, identical, carboxylate group. Unless excess base is added, no other ( -)436-(3-malonate complex is isolated. These results represent the first instance of absolute31 chiral recognition of a prochiral center by a small molecule (a character-

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