The structures of asparenomycins A, B and C, produced by Streptomyces tokunonensis sp. nov. and Streptomyces argenteolus, were elucidated as new carbapenem antibiotics having a hydroxyisopropylidene group on the β-lactam ring. The stereochemistry was unequivocally confirmed by X-ray analysis and chemical degradation. ASM A (main component) was assigned structure Ib via 1H/13C NMR, FD-MS, esterification/acetylation experiments, and its p-nitrobenzyl acetate derivative was used for X-ray crystallography which confirmed the R-configuration at C(5) and E-geometry at C(8). ASM C, isolated from less hydrophilic fractions, was proved to be deoxy ASM A (structure IIIb) by deoxygenating ASM A with TiCl3 (yielding a product identical to ASM C in HPLC and antibacterial properties). ASM B, a minor component, was inferred as dihydro ASM A (structure IIb) from 1H NMR data (lacking vinyl protons but having methylene protons) and biogenetic considerations, with configurations at C(5) and S atom likely same to ASM A. The E geometry of the hydroxyisopropylidene group was supported by the hydrolytic product of ASM A being a diacid (IV) rather than a lactone, consistent with NMR data. Thus, the structures of ASM A, B and C were determined to be Ib, IIb and IIIb, respectively.