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Journals and Conferences
6. Third-Generation Biomimetic Synthesis 2300 6.1. C23′-Deoxy South Unit of Cephalostatin 1 2302 6.2. South Hemisphere of Cephalostatin 7 2304 7. Related Syntheses 2305 8. Structure-Activity Relationships 2306 8.1. Appropriate Pairing of Polar/Nonpolar Subunits 2306 8.2. Homoallylic Oxygen 2307 8.3. 17-OH Function Is Beneficial 2308 8.4. An Aromatic Moiety… (More)
[structure: see text] 20- and 25'-epimers of cephalostatin 7, prepared by directed unsymmetrical pyrazine synthesis, address outer-ring topographical and stability questions and intimate an oxacarbenium ion rationale for the role in bioactivity of the spiroketal (E/F, E'/F') rings of this class of antitumor agents.
Oxidative functionalization (or removal) of a steroidal C18 methyl group is possible using a previously unknown dyotropic rearrangement of a seven-membered fused C-ring lactone to a 6-ring spiro lactone. Spiroketal equilibration led to the 23-deoxy South analogue of cephalostatin 1 (1) in only 12 steps (23% overall yield) from hecogenin acetate 4, and to… (More)
The structure of the North spiroketal moiety of ritterazine M has been corrected from 1a to 1b. This was accomplished by comparison of published spectra of the natural product with five synthetic spiroketal-alcohols. Synthesis of these models was efficiently accomplished by reductive cleavage of the spiroketal and Sharpless asymmetric dihydroxylation of an… (More)
We are developing methods that restrict the conformational mobility of peptides and related heteropolymers while simultaneously altering their properties. Our experiments occur as processes wherein a conserved, lipophilic reagent is activated in stages to form composite products with unprotected polyamides in parallel. For each starting oligomer, the goal… (More)
Antineoplastic bis-steroidal (cephalostatin-type) analogues of the saponin OSW-1 were produced from a dihydroaglycone of OSW-1. The key aglycone 6H was obtained from 5alpha-androstan-3beta-ol-17-one in 8 steps (38% yield). The SAR of the aglycones, intermediates, and hybrid analogues provide insights regarding the proposed common role of C22-oxocarbenium… (More)
Analogues 12'beta-hydroxycephalostatin 1 (9), 7'-deoxyritterazine G (10), and 14-epi-7'-deoxyritterazine B (11) were prepared via our protocol for unsymmetrical pyrazine synthesis. Cytotoxicity against human tumors was also determined for the first time for ritterazines, with femtomolar potency and a high correlation to cephalostatins observed. The SAR of… (More)
[formula: see text] Lewis and/or Bronsted acid additives permit ring opening and halogenation of spiroketals at substantially reduced temperatures to produce omega-iodo enol ethers in improved yield and purity, which can undergo further reaction in the presence of distal electrophilic centers to give new steroid skeletons.