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971.
Chiral BINOL-derived diols catalyze the enantioselective asymmetric allylboration of acyl imines. The reaction requires 15 mol % (S)-3,3'-Ph2-BINOL as the catalyst and allyldiisopropoxyborane as the nucleophile. The reaction products are obtained in good yields (75-94%) and high enantiomeric ratios (95:5-99.5:0.5) for aromatic and aliphatic imines. High diastereoselectivities (diastereomeric ratio > 98:2) and enantioselectivities (enantiomeric ratio > 98:2) are obtained in the reactions of acyl imines with crotyldiisopropoxyboranes. This asymmetric transformation is directly applied to the synthesis of Maraviroc, the selective CCR5 antagonist with potent activity against HIV-1 infection. Mechanistic investigations of the allylboration reaction including IR, NMR, and mass spectrometry studies indicate that acyclic boronates are activated by chiral diols via exchange of one of the boronate alkoxy groups with activation of the acyl imine via hydrogen bonding. 相似文献
972.
973.
Dang Q Kasibhatla SR Reddy KR Jiang T Reddy MR Potter SC Fujitaki JM van Poelje PD Huang J Lipscomb WN Erion MD 《Journal of the American Chemical Society》2007,129(50):15491-15502
Excessive glucose production by the liver coupled with decreased glucose uptake and metabolism by muscle, fat, and liver results in chronically elevated blood glucose levels in patients with type 2 diabetes. Efforts to treat diabetes by reducing glucose production have largely focused on the gluconeogenesis pathway and rate-limiting enzymes within this pathway such as fructose-1,6-bisphosphatase (FBPase). The first potent FBPase inhibitors were identified using a structure-guided drug design strategy (Erion, M. D.; et al. J. Am. Chem. Soc. 2007, 129, 15480-15490) but proved difficult to deliver orally. Herein, we report the synthesis and characterization of a series of orally bioavailable FBPase inhibitors identified following the combined discoveries of a low molecular weight inhibitor series with increased potency and a phosphonate prodrug class suitable for their oral delivery. The lead inhibitor, 10A, was designed with the aid of X-ray crystallography and molecular modeling to bind to the allosteric AMP binding site of FBPase. High potency (IC50 = 16 nM) and FBPase specificity were achieved by linking a 2-aminothiazole with a phosphonic acid. Free-energy perturbation calculations provided insight into the factors that contributed to the high binding affinity. 10A and standard phosphonate prodrugs of 10A exhibited poor oral bioavailability (0.2-11%). Improved oral bioavailability (22-47%) was achieved using phosphonate diamides that convert to the corresponding phosphonic acid by sequential action of an esterase and a phosphoramidase. Oral administration of the lead prodrug, MB06322 (30, CS-917), to Zucker Diabetic Fatty rats led to dose-dependent inhibition of gluconeogenesis and endogenous glucose production and consequently to significant blood glucose reduction. 相似文献
974.
Scott WL Martynow JG Huffman JC O'Donnell MJ 《Journal of the American Chemical Society》2007,129(22):7077-7088
A wide variety of highly substituted lactam containing peptidomimetic scaffolds are prepared by solid-phase synthesis from a single, versatile class of resin-bound aldehyde intermediates (1). These include monocyclics 3, bicyclics 4, tricyclics 5, and tetracyclics 6. The key intermediate 1 is readily synthesized from resin-bound natural or unnatural alpha-amino acids. The synthetic procedures permit the construction of a large diversity of substitution patterns for ready use in combinatorial chemistry. In every case, the release of final products from resin is by a cyclitive cleavage process. Since this depends on successful completion of multiple intermediate synthetic steps, the products are often quite pure, even though previous steps involve only a filtration workup. The mild conditions for many of these synthetic procedures offer the promise of using this chemistry in peptide fragment condensations to produce modified peptides, at either the N-terminus or C-terminus, or as individually assembled peptide segments with a wide variety of conformationally restricted peptidomimetic linkers at the point of juncture. 相似文献
975.
Polyfluorenes without monoalkylfluorene defects 总被引:4,自引:0,他引:4
Cho SY Grimsdale AC Jones DJ Watkins SE Holmes AB 《Journal of the American Chemical Society》2007,129(39):11910-11911
976.
Kulikov has given an étale morphism of degree d > 1 which is surjective modulo codimension two with X simply connected, settling his generalized jacobian problem. His method reduces the problem to finding a hypersurface and a subgroup of index d generated by geometric generators. By contrast we show that if D has simple normal crossings away from a set of codimension three and meets the hyperplane at infinity transversely, then necessarily d = 1.
Received: 21 November 2006 相似文献
977.
In this paper, we establish bounds on the degree of a symmetric polynomial p = p(x) = p(x
1,..., x
g
) (with real coefficients) in g noncommuting (nc) variables x
1,..., x
g
in terms of the “signature” of its Hessian
which is a polynomial in x and h = (h
1,..., h
g
) homogeneous of degree 2 in h. The bounds are obtained by exploiting the interplay between assorted representations for p(x) and p″(x)[h] that are developed in the paper. In particular, p″(x)[h] admits a representation of the form
where f
j
+
, f
j
−
are nc polynomials. Such representations are highly non-unique. However, there is a unique smallest number of positive (resp.,
negative) squares σ
±
min
required in an SDS decomposition of p″(x)[h]. Our main results yield the following corollary and a number of refinements.
Supported by a Jay and Renee Weiss Chair.
Partly supported by the NSF and the Ford Motor Co.
Partly supported by the NSF grants DMS-0140112 and DMS-0457504. 相似文献
978.
Abstract Let p be a prime integer and M a Krull monoid with divisor class group
. We represent by S the set of nontrivial divisor classes of
which contain prime divisors. We present a new inequality for the elasticity of M (denoted ρ (M)) which is dependent on the cardinality of S and argue that this inequality is the best possible. If M as above has | S| = 3, then it is known that
, but for large p, not all the values in this containment set can be realized. For each | S| = 3, we produce a submonoid
of
such that
Keywords: Krull monoid, Block monoid, Elasticity of factorization
Mathematics Subject Classification (2000): 20M14, 20D60, 13F05 相似文献
979.
This paper continues the study begun in [GEROLDINGER, A.: On non-unique factorizations into irreducible elements II, Colloq. Math. Soc. János Bolyai 51 (1987), 723–757] concerning factorization properties of block monoids of the form ℬ(ℤ
n
, S) where S =
(hereafter denoted ℬ
a
(n)). We introduce in Section 2 the notion of a Euclidean table and show in Theorem 2.8 how it can be used to identify the irreducible elements of ℬ
a
(n). In Section 3 we use the Euclidean table to compute the elasticity of ℬ
a
(n) (Theorem 3.4). Section 4 considers the problem, for a fixed value of n, of computing the complete set of elasticities of the ℬ
a
(n) monoids. When n = p is a prime integer, Proposition 4.12 computes the three smallest possible elasticities of the ℬ
a
(p).
Part of this work was completed while the second author was on an Academic Leave granted by the Trinity University Faculty
Development Committee. 相似文献
980.
A new method is described for effecting ion/ion proton transfer reactions that involves storage of analyte ions while oppositely charged ions are transmitted through the stored ion population. In this approach, the products are captured and stored in the linear ion trap for subsequent mass analysis. Charge reduction of multiply charged protein ions is used as an example to illustrate the analytical usefulness of this method. In another variation of the transmission mode ion/ion reaction approach, two charge inversion experiments, implemented by passing analyte ions through a population of multiply charged reagent ions in a LIT, are also demonstrated. A pulsed dual ion source approach coupled with a hybrid triple quadrupole/linear ion trap instrument was used to demonstrate these two methods. The results for ion/ion reactions implemented using these so-called "transmission mode" experiments were comparable to those acquired using the more conventional mutual storage mode, both in terms of efficiency and information content of the spectra. An advantage of transmission mode experiments compared with mutual storage mode experiments is that they do not require any specialized measures to be taken to enable the simultaneous storage of oppositely charged ions. 相似文献