Georg Albers-Schönberg

Isolation and structure of chaetomellic acids A and B from Chaetomella acutiseta: farnesyl pyrophosphate mimic inhibitors of ras farnesyl-protein transferase

Abstract Farnesyl-Protein transferase catalyses a post-translational modification of Ras that is obligatory for the cell transforming activity of this oncogene protein. The screening of natural products to identify inhibitors of this enzyme as a potential anticancer agents, has led to the isolation of two novel dicarboxylic acids, named chaetomellic acids from Chaetomella acutiseta, as potent and selective inhibitors which appear to be the first examples of nonphosphorous containing FPP mimics.

Neocarzinostatin chromophore: Presence of a highly strained ether ring and its reaction with mercaptan and sodium borohydride

Spectroscopic evidence suggests the presence of a highly strained ether ring (Fig. 1) (possibly an epoxide) in the C12-subunit of the previously determined partial structure 2a (Fig. 2) of the major neocarzinostatin chromophore (NCS-Chrom A) which completes assignment of all the oxygens in the molecule. The main product from mercaptan treatment suggests opening of the ether ring involving the addition of one molecule of mercaptan as well as reduction of the C12-substructure, whereas a parallel two-step reduction occurs on NaBH4 treatment. Both reactions occur with rearrangement of the C12-substructure and the implication for the mechanism of action of NCS-Chrom A in DNA strand scission activity is discussed. The evidence suggests a downward revision of the molecular formula for NCS-Chrom A as well as minor components B and C by two protons.

Neocarzinostatin: Chemical characterization and partial structure of the non-protein chromophore

Abstract The molecular formula C35H35NO12 (mol.wt. 661) is proposed for the biologically active chromophoric component of neocarzinostatin. The partial structure 2 is proposed based on 1 H NMR and mass spectral data and consists, in part, of a 2,6-dideoxy-2-methylamino-galactose moiety and a naphthoic acid derivative. Special treatments required to obtain spectral data of the labile chromophore are described.

Neocarzinostatin chromophore: Presence of a cyclic carbonate subunit and its modification in the structure of other biologically active forms

Abstract On the basis of spectroscopic evidence, opening of a five-membered cyclic carbonate ring (1,3-dioxolan-2-one) in the C15-subunit of the previously determined partial structure 1 (Fig. 1) of the major neocarzinostatin chromophore (NCS-Chrom A ), is proposed to account for its base-catalyzed methanolysis to NCS-Chrom C . NCS-Chrom B , apparently an authentic natural product present as a minor component in all preparations of NCS studied, was found to be formally equivalent to the hydrolysis/decarboxylation product of the cyclic carbonate functionality in NCS-Chrom A . The mercaptan-dependent DNA strand-scission activity, equivalent for NCS-Chrom A , B and C , is independent of the integrity of the cyclic carbonate ring system and implicates a secondary site in the C15-substructure for mercaptan activation.