The title compound, CI7H28N407, is a synthetic crystalline cyclic tetrapeptide containing alternate 0c-amino peptide groups and fl-amino peptide groups similar to the naturally occurring depsipeptide serratamolide. The tetrapeptide represents a preliminary step in the proposed synthesis of a cylindrical polypeptide. The 14-membered 'ring' consists of four planar segments with each segment in the trans conformation. The corner atoms are C'(1), Ca(2), C~(3) and Ca(4). Two carbonyl oxygens are directed above the average plane of the ring and the other two below. If the side chains are disregarded, two of the peptide groups are related to the other two by an approximate center of symmetry. In the crystal the molecules are stacked over each other by translation in the a direction. Between each pair of molecules in the stack there are two NH. • • O bonds at 2-86 A. The remaining two NH moieties do not participate in hydrogen bonding. The space group is P21 with a=5.624 (4), b= 10.298 (7), c= 17.859 (13) A, and fl= 99"07 (5) °. The structure was solved by the symbolic addition procedure.

The structures of aspertetronin A (C16H2004) and aspertetronin 8 (C16H2,06), metabolites of a mutant strain of Aspergillus rugulosus, have been elucidated. The use of both high-resolution l H n.m.r. spectroscopy (220 Mc./ sec. and spin decoupling) and ' element-map ' mass spectrometry have proved determining in establishing that the metabolites are the novel acyltetronic acid derivatives (XXI I) and (XXI I I) respectively.

No abstract

Monamycin, a crystalline antibacterial preparation isolated from cultures of Streptomycesjamaicensis, consists of a mixture of fifteen cyclohexadepsipeptides, six of which contain chlorine. Each molecular species consists of one residue of a-hydroxy-acid (either L-2-hydroxy-3-methylbutanoic acid or L-2-hydroxy-3-methylpentanoic acid) and five residues of a-amino-or imino-acid. The latter consist of N-methyl-D-leucine, L-proline (or trans-4-methyl L-proline), D-isoleucine (or D-valine), (3R)-piperazic acid [or (3R,5S)-5-chloropiperazic acid, or (3R)-4,5 (or 5,6) -dehydropiperazic acid], and (3S,5S) -5-hydroxypiperazic acid. The name piperazic acid is assigned to * A preliminary account of this observation has been publ i ~h e d . ~

No abstract