Asymmetric Total Synthesis of Propindilactone G.

A concise total synthesis of (+)-propindilactone G, a nortriterpenoid isolated from the stems of Schisandra propinqua var. propinqua, has been achieved for the first time. The key steps of the synthesis include an asymmetric Diels-Alder reaction, a Pauson-Khand reaction, a Pd-catalyzed reductive hydrogenolysis reaction, and an oxidative heterocoupling reaction. These reactions enabled the synthesis of (+)-propindilactone G in only 20 steps. As a consequence of our synthetic studies, the structure of (+)-propindilactone G has been revised.

Total synthesis of (±)-decinine via an oxidative biaryl coupling with defined axial chirality.

The total synthesis of (±)-decinine has been achieved. The key steps in the synthesis involved the formation of lasubine II via a gold catalyzed annulation of 1-(but-3-yn-1-yl)piperidine and the formation of the 12-membered ring of decinine (1) with complementary atropselectivity via a VOF3-mediated oxidative biaryl coupling reaction.

Diastereoselective total synthesis of (±)-schindilactone†A, Part†1: Construction of the ABC and FGH ring systems and initial attempts to construct the CDEF ring system.

First-generation synthetic strategies for the diastereoselective total synthesis of schindilactone A (1) are presented and methods for the synthesis of the ABC, FGH, and CDEF moieties are explored. We have established a method for the synthesis of the ABC moiety, which included both a Diels-Alder reaction and a ring-closing metathesis as the key steps. We have also developed a method for the synthesis of the FGH moiety, which involved the use of a Pauson-Khand reaction and a carbonylative annulation reaction as the key steps. Furthermore, we have achieved the construction of the central 7-8 bicyclic ring system by using a [3,3]-rearrangement as the key step. However, unfortunately, when this rearrangement reaction was applied to the construction of the more advanced CDEF moiety, the anticipated annulation reaction did not occur and the development of an alternative synthetic strategy would be required for the construction of this central core.

Diastereoselective total synthesis of (±)-schindilactone†A, Part†2: Construction of the fully functionalized CDEFGH ring system.

The successful synthesis of the highly complex model compound (2) of the CEFGH ring system of schindilactone A (1) is described. Several synthetic methodologies were developed and applied to achieve this goal, including ring-closing metathesis (RCM) and Co-thiourea-catalyzed Pauson-Khand reactions. Furthermore, two independent approaches were developed for the construction of the GH ring of model compound 2, the key steps of which included Pd-thiourea-catalyzed carbonylative annulation, methylation, and sequential RCM/oxa-Michael-addition reactions. The chemistry developed herein has provided a greater understanding of the synthesis of schindilactone A (1) and its analogous compounds of the same family.

Diastereoselective total synthesis of (±)-schindilactone†a, Part†3: The final phase and completion.

The final phase for the total synthesis of (±)-schindilactone A (1) is described herein. Two independent synthetic approaches were developed that featured Pd-thiourea-catalyzed cascade carbonylative annulation reactions to construct intermediate 3 and a RCM reaction to make intermediate 4. Other important steps that enabled the completion of the synthesis included: 1) A Ag-mediated ring-expansion reaction to form vinyl bromide 17 from dibromocyclopropane 30; 2) a Pd-catalyzed coupling reaction of vinyl bromide 17 with a copper enolate to synthesize ketoester 16; 3) a RCM reaction to generate oxabicyclononenol 10 from diene 11; 4) a cyclopentenone fragment in substrate 8 was constructed through a Co-thiourea-catalyzed Pauson-Khand reaction (PKR); 5) a Dieckmann-type condensation to successfully form the A ring of schindilactone A (1). The chemistry developed for the total synthesis of schindilactone A (1) will shed light on the synthesis of other family members of schindilactone A.

Organopalladium(IV) chemistry.

Although the chemistry of Pd(0), Pd(I) and Pd(II) is well established, high oxidation state Pd(IV) complexes are less well-known. This situation has highly changed in recent years. Many well-defined Pd(IV) complexes has been isolated and characterized, providing evidence for a series of proposed Pd(II)/Pd(IV) catalytic reactions. A deep understanding of the behavior of Pd(IV) complexes could lead to the design and development of novel reactions that could not be accessed by traditional Pd(0)/Pd(II) chemistry. This critical review describes the stoichiometric reactions of Pd(IV) complexes and discusses their potential mechanism in catalytic reactions (137 references).

[Experimental study of DNA synthesis in the airway cells and airway remodeling in asthmatic rats].

OBJECTIVE: To study the DNA synthesis in the airway cells of asthmatic rats after allergen stimulation in association with airway remodeling. METHODS: Double staining immunohistochemical techniques was used to determine DNA synthesis of the airway cells of 12 asthmatic and 12 normal rats. BrdU incorporation into the airway smooth muscle (ASM) and epithelium was quantified by employment of computer-assisted image analysis. RESULTS: BrdU indices in both the ASM and the epithelium of asthmatic model group were higher than those of the control group (P<0.01, P<0.05), and positive linear correlation of the BrdU indices in the ASM and epithelium with the airway diameter was observed (r=0.7828, P<0.01; r=0.5852, P<0.05), which was not found in the control group (r=-0.3755, P>0.05; r=-0.5208, P>0.05). The epithelial thickness of the model group was significantly greater than that of the control group (P<0.01). There was no significant difference in terms of airway diameter, thickness of the ASM and the area positive of alpha-smooth muscle actin between the 2 groups (P>0.05). CONCLUSION: Increased DNA synthesis and accelerated proliferation of ASM and epithelial cells in sensitized SD rats following repeated allergen challenges may lead to airway remodeling.