Ristocetins A and B, elaborated by Nocardia lurida, 1 and related antibiotics are glycopeptides which inhibit cell wall biosynthesis in Gram positive bacteria by a mechanism involving complexation with peptide intermediates.2 The site of activity in the ristocetins has been shown to reside in the peptide portion which comprises complex and unusual amino acids.3 A previous report from this laboratory described the structure of one of the constituents (1) of ristocetin A which has two a-aminoarylacetic acid fragments joined via an ether linkage between the aromatic rings.4 We now wish to report the isolation and identification of a second constituent (2), in this case containing two cr-aminoarylacetic acids joined through a biphenyl inkage. Hg2H Hg2H 4' H2NCHC02H 1 2 Tarbell and coworkers have reported obtaining by ion-exchange chromatography of hydrolysates of ristocetin A a bis(amino acid) for which the empirical formula Cl6Hl6N207 was assigned by mass spectrometry using diethyl esters of bis(t-BOC) and bis(thio-t-BOC) derivatives.5 The similarity of this bis(amino acid) to 1 led them to suggest that the compound might be a normethyl homolog but further structural assignments were not made. In the present study the nor-methyl bis(amino acid) was isolated from ristocetin A as derivative 3 by hydrolysis (aq 6M HCl/HOAc 2:1, reflux, 48 hr or aq 4M KOH, 1.8M NaBH4, reflux, 24 hr) of N-acetylated 0-methylated aglycoristocetin followed by derivatization as the N-acetyl methyl esters. Careful separation by hplc (Waters P-Porasil, MeOH/CH2C12 3:97) resolved two diastereoisomers of 3 from each other and from other constituents of the mixture including the diastereoisomers 4 derived from bis(amino acid) 1.6 Compounds 3 and 4 have the same empirical formula but the stereoisomers of 3 were readily distinguished from those of 4 by nmr on the basis of the number of O-methyl groups and the lack of an aryl C-methyl group. Samples of the nor-methyl amino acid' were derivatized by acetylation (AcpO in MeOH, 0" warming to 20ยฐ) and