STRUCTURE AND MODE OF ACTION OF THE ANTIBIOTIC RISTOCETIN-A

The antibiotics ristocetin A and ristomycin A are shown to be identical. It is concluded that ristocetin A is constituted from six sugars and an aglycone portion based on (i) a bis-ether containing three benzenoid rings, (ii) a fragment which on hydrolysis affords a 2′,4,6-trihydroxybiphenyl-2, 3′-diyldiglycinate derivative, (iii) a previously isolated fragment incorporating a biphenyl ether, and (iv) at least one (and perhaps two) moles of potential glycine from alkaline hydrolysis. An approximate molecular-weight determination (2 063 ± 5 Daltons) of the antibiotic by californium plasma desorption mass spectrometry, 13C, and 1H n.m.r. spectra, and functional group determinations, are consistent with the incorporation of the above structural units in a tetracyclic aglycone structure. A cellwall component analogue, acetyl-D-alanyl-D-alanine, forms with ristocetin A a complex whose dissociation [in (CD3)2SO solution at 40 °C] is slow on the 1H n.m.r. time scale.