Composition and Origin of Shallow Biogenetic Gases in the Baise Basin, South China

Based on the analytical data of over 30 gas samples, combined with geochemical and geological backgrounds, the composition and distribution characteristics of shallow biogenetic gases in the Baise Basin, a Tertiary residual basin in southern China, were extensively investigated, and the origin and formation mechanism tentatively approached. The shallow gases are primarily composed of gaseous hydrocarbons, generally accounting for over 90%. The abundances of methane and C2＋ homologues show a relatively wide range of variation, mainly 50%-100% and 0%-50%, respectively, depending on the mixing proportions between biogenetic and thermogenic gases. A highly negative carbon isotope is the significant signature for the shallow gases with δ^13C1 values of -55‰ to -75‰. According to molecular and isotopic compositions and light hydrocarbon parameters, the shallow gases in the basin can be classified into three types of origins： biogenetic gas, biogenetic/thermogenic mixed gas, and oii-biodegraded gas. They exhibit regular distribution both spatially and temporally, and are believed to be associated with the maturity of adjoining gas source rocks and biodegraded oil accumulation. The Baigang and Nadu source rocks can be considered to have experienced early and late gas generation during early burial and after basin uplift respectively. A late accumulation mechanism of multiple gas sources is put forward for the formation of the shallow gas reservoirs, which is responsible for the variations in chemical and isotopic composition of the gases in depth profile.

The special sealing mechanism of caprock for Quaternary biogenetic gas in Sanhu area,Qaidam Basin,China

The Quaternary biogenetic gas reservoirs in the east of Qaidam Basin have many characteristics such as late forming time,shallow burial depth,low diagenetic grade,high porosity and high permeability and so on.It cannot be considered as caprock according to the traditional evaluation criterion.However, the large scale and high efficient biogenetic gas reservoirs of the Qaidam Basin are really formed under these kinds of caprocks,so it does have some specialty in its sealing mechanism.Aiming at the special sealing mechanism,some simulating experiments have been done.The research results show that the sealing ability of biogenetic gas caprock is related with water saturation,the caprock that is saturated with salt water can effectively block seepage and diffusion.Furthermore,the multiple reservoir-caprock groups have accumulated sealing effect,causing the formation of big gas fields.The evaluation method with traditional caprock parameters cannot be adopted in evaluating the study area.

Sesquiterpenes from the soft coral Paralemnalia thyrsoides and their biogenetic correlation

Terpenoids are the important secondary metabolites of soft coral. In the investigation of soft corals collected from South China Sea, we have found many cembranoid diterpenes with bioactivity and two rare unique biscembranoid tetraterpenes, i.e. methyl sartortuoate and methyl isosartortuoate. We have suggested a plausible biogenesis pathway for these two tetraterpenoids in the soft coral Sarcophyton tortuosum.Recently, B. F. Bowden et al. obtained one more tetraterpenoid with the similar structure from the same species Australian soft coral. Besides, they isolated one of the probably

Biogenetic Pathways for Marine Terpenoids

A reasonable theoretical elucidation of biogenetic pathways is given for marine ter-penoids——halogenated terpenoids,cernbranolides and tetracyclic tetraterpenoids in marine organisms ac-cording to biogenesis,and the possibility of studying biogenetic pathways by chemical synthesis and molecu-lar probe method is discussed.

Chemistry and biology of Pestalotiopsis-derived natural products

Species within the fungal genus Pestalotiopsis have become a topic of research in many microbial-chemical and pharmacological laboratories because they contain structurally complex,biologically active metabolites.This article is a follow-up to a previous review(Xu,Ebada,and Proksch,Fungal Divers 44:15–31,2010).It focuses particularly on new findings concerning the chemistry and bioactivity of Pestalotiopsis sp.,covering a period ranging from August 2010 to August 2013.Some 160 metabolites were isolated from Pestalotiopsis species during this period and their structures are reported within a biogenetic context.Bioassays showed antitumor,antifungal,and antimicrobial activities to be the most notable bioactivities of secondary metabolites isolated from this genus.The biogenetic pathways associated with the alkaloids,sesquiterpenes,quinines,xanthones,and lactones covered in this review are highlighted.

Macleayine,a new alkaloid from Madeaya cordata

Macleayine （1）, a new natural occurring alkaloid with a unique spiro [furanone-piperidinedione] framework, was isolated from the aerial parts ofMacleaya cordata. Its unusual structure was established by extensive spectroscopic analyses, computer-assisted structure elucidation software （ACD/Structure Elucidator）, quantum chemistry calculations and ECD calculation. The result of virtual molecular docking predicted the compound can enhance the effects of insulin, and may be used to treat tvpe II diabetes.

Sesquiterpenes from Alisma plantago-aquatica

Six sesquiterpenes, including three guaiane type sesquiterpenes （1-3）, one oplopanone type sesquiterpene （4）, one xanthane type sesquiterpene （5） and one salvialane type sesquiterpene （6）, were isolated from Alisma plantago-aquatica for the first time. The structures of these six compounds were elucidated as alismoxide （1）, alismol （2）, orientalol B （3）, oplopanone （4）, gibberodione （5）, and 7a, lOa-epoxy-salvialan-1Ofl-ol （6）, respectively, among which 6 was a new natural product. Xanthane type and salvialane type sesquiterpenes were obtained from the genus Alisma for the first time. In addition, a plausible biosynthetic pathway for all isolates was discussed.

Alkaloid constituents from the fruits of Flueggea virosa

Three new indole alkaloids, flueindolines A–C(1–3), along with nine known alkaloids(4–12), were isolated from the fruits of Flueggea virosa(Roxb. ex Willd.) Voigt. Compounds 1 and 2 are two new fused tricyclic indole alkaloids possessing an unusual pyrido[1, 2-a]indole framework, and 3 presents a rare spiro(pyrrolizidinyl-oxindole) backbone. Their structures with absolute configurations were elucidated by means of comprehensive spectroscopic analysis, chemical calculation, as well as X-ray crystallography. Chiral resolution and absolute configuration determination of the known compounds 4, 10, and 11 were reported for the first time. The hypothetical biogenetical pathways of 1–3 were herein also proposed.