2,265 research outputs found
Total syntheses of ?-lactone containing natural products: I. total synthesis of belactosin C II. synthetic studies toward spongiolactone
The recently isolated bacterial metabolites, belactosins A-C from a fermentation
broth of Streptomyces sp. UCK14, uniquely contain a β-lactone dipeptide motif and
exhibit anticancer activities. The enantioselective synthesis of (-)-belactosin C and
derivatives was accomplished in a concise manner employing the tandem, Mukaiyama
aldol-lactonizaton (TMAL) process and test their bioactivities. . One approach involved
a distal double diastereoselective TMAL reaction with a dipeptide glyoxamide, whereas
a second approach involved amide coupling of a dipeptide with a β-lactone carboxylic
acid, obtained via the TMAL process employing a chiral silyl ketene acetal. Enzymatic
assays showed that the belactosins act as the dual inhibitors of the proteasome and the
thioesterase domain of fatty acid synthase.
Spongiolactone which uniquely contains a cyclopentyl-fused β-lactone was
isolated in 1986 from Spongi-onellagracilis No biological activity have been reported
for this compound; however, the acylating potential of the resident β-lactone warrants
screening for potential activity. After many setbacks in the synthesis of spongiolactone,
significant progress has been made. Importantly, NCAL process also enabled a concise construction of [3.2.0]-bicyclo β-lactone, which is the key structure in the
spongiolactone synthesis and only a few steps remained to complete the synthesis
Single-Copy Certification of Two-Qubit Gates without Entanglement
A quantum state transformation can be generally approximated by single- and
two-qubit gates. This, however, does not hold with noisy intermediate-scale
quantum technologies due to the errors appearing in the gate operations, where
errors of two-qubit gates such as controlled-NOT and SWAP operations are
dominated. In this work, we present a cost efficient single-copy certification
for a realization of a two-qubit gate in the presence of depolarization noise,
where it is aimed to identify if the realization is noise-free, or not. It is
shown that entangled resources such as entangled states and a joint measurement
are not necessary for the purpose, i.e., a noise-free two-qubit gate is not
needed to certify an implementation of a two-qubit gate. A proof-of-principle
demonstration is presented with photonic qubits.Comment: 8 pages. arXiv admin note: text overlap with arXiv:1812.0208
Student Progression Through Developmental Sequences in Community Colleges
Developmental education is designed to provide students with weak academic skills the opportunity to strengthen those skills enough to prepare them for college-level coursework. The concept is simple enough—students who arrive unprepared for college are provided instruction to bring them up to an adequate level. But in practice, developmental education (or “remedial” education, we use these terms interchangeably) is complex and confusing. Experts do not agree on the meaning of being “college ready,” and policies governing assessment, placement, pedagogy, staffing, completion, and eligibility for enrollment in college-level, credit-bearing courses vary from state to state, college to college, and program to program. The developmental education process is confusing enough simply to describe, yet from the point of view of the student, especially one with very weak academic skills and little previous success in school, it may appear as a bewildering set of unanticipated obstacles involving several assessments, classes in more than one subject area, and sequences of courses requiring three or more semesters of study before the student (often a high school graduate) is judged prepared for college-level work
Correlated electronic states at domain walls of a Mott-charge-density-wave insulator 1T-TaS2
Domain walls in interacting electronic systems can have distinct localized
states, which often govern physical properties and may lead to unprecedented
functionalities and novel devices. However, electronic states within domain
walls themselves have not been clearly identified and understood for strongly
correlated electron systems. Here, we resolve the electronic states localized
on domain walls in a Mott-charge-density-wave(CDW) insulator 1T-TaS2 using
scanning tunneling spectroscopy. We establish that the domain wall state
decomposes into two nonconducting states located at the center of domain walls
and edges of domains. Theoretical calculations reveal their atomistic origin as
the local reconstruction of domain walls under the strong influence of electron
correlation. Our results introduce a concept for the domain wall electronic
property, the wall's own internal degrees of freedom, which is potentially
related to the controllability of domain wall electronic properties
- …