The structure of bacilysin and other products of Bacillus subtillis

1. Mass spectra of the trimethylsilyl derivative and the methyl ester of the N-trifluoroacetyl derivative of bacilysin indicated that the antibiotic had a molecular weight of 270. Several peaks in the spectrum of the methyl ester were consistent with the presence of an N-terminal alanine residue in the molecule. 2. The proton-magnetic-resonance spectrum of bacilysin confirmed that the antibiotic contained an epoxide group and the spin–spin splitting of the protons of the epoxide group indicated that the side chain of the epoxycyclohexanone ring was attached at C-4 and was αβ to the keto group. 3. The formation of an αβ-unsaturated ketone on reduction of bacilysin with chromous chloride also showed that the epoxide was αβ to the keto group. 4. The optical-rotatory-dispersion curve of bacilysin showed a positive Cotton effect. On the assumption that the reversed Octant rule for αβ-epoxyketones was applicable this revealed the absolute stereochemistry and enabled a definitive structure to be assigned to the molecule. 5. Similar measurements showed that substance AA1, isolated from culture supernatants, was the C-terminal amino acid of bacilysin. 6. Hydrolysis of substance P2 with leucine aminopeptidase and the mass spectrum of the methyl ester of its N-trifluoroacetyl derivative showed that this substance was l-analyl-l-alanine. 7. These results are discussed in relation to the biogenesis of bacilysin.

Some remarks on the interpretation of natural and magnetically induced optical activity data

1. Introduction—A classification for optically active chromophores One of the most useful concepts that emerges from the perturbation approach to the theory of natural optical activity is that of the ‘rotational strength’ of a transition (Condon 1937). This signed quantity conveniently and effectively measures how strongly a particular transition contributes to both the dispersive and absorp­tive aspects of the optical activity of a molecule (Moscowitz 1962); it is obtainable experimentally from either the pertinent partial optical rotatory dispersion curve or the partial circular dichroism curve (Djerassi 1960), and it is amenable to theo­retical calculation for homogeneous isotropic media as the following scalar product (Condon 1937; Moscowitz 1962; Djerassi 1960; Rosenfield 1928). R ba = I {( a | μ e | b ). ( b | μ m | a )}. Here ( a | μ e | b ) and ( b | μ m | a ) are the electric and magnetic dipole transition moments, respectively, connecting the ground state a and the excited state b , and I means imaginary part. Accessible as such to both theory and experiment, the rotational strength provides one of the most suitable foundations on which to build quanti­tative correlations between optical activity data and molecular structure.