Quasi-Symmetric Designs with Good Blocks and Intersection Number One

We show that a quasi-symmetric design with intersection numbers 1 and y > 1 and a good block belongs to one of three types: (a) it has the same parameters as PG ₂(4, q), the design of points and planes in projective 4-space; (b) it is the 2-(23, 7, 21) Witt design; (c) its parameters may be written v = 1 + (( – 1) + 1)(y – 1) and k = 1 + (y – 1), where is an integer and > y 5, and the design induced on a good block is a 2-(k, y, 1) design. No design of type (c) is known; moreover, for large ranges of the parameters, it cannot exist for arithmetic reasons concerning the parameters. We show also that PG ₂(4, q) is the only design of type (a) in which all blocks are good.     

Preparation and properties of triorganostannylmethyl 2,3:5,6-di-O-isopropylidene-α-D-mannofuranosides; pesticidal and fungicidal activities of triphenylstannyl-carbohydrate derivates

The synthesis of trioganostannylmethyl 2,3:5,6-di-O-isopropylidene-α-D-mannofuranoside (compound 3, R*OCH₂SnR₂R′:R?R′?Me or Ph) from D-mannose is reported. The compound 3 (R?R′?Ph) is transmetallated by PhLi to compound 5, R*OCH₂Li, Which can be trapped by HgCl₂ [as (R*OCH₂)₂Hg] and by ketones, R³COMe [as compound 7, R*OCH₂CR³MeOH]. Two stereoisomers of this compound (7a, R³?Ph) were formed in a ratio of 40:60, indicating some asymmetric induction, arising from the chiral R* moiety. Reactions of compound 3, (R?R′?Ph), with I₂, HO₂CCF₃ and Cl₂PtCOD result in Ph–Sn bond cleavage and formation of compound 3 with R?Ph; R′?I, OCOCF₃ and Cl respectively. Reactions of compound 3 (R?R′?Me) with electrophiles can lead to cleavage of either of both types of C–Sn bonds present (e.g. by I₂, Br₂, Cl₂PtCOD or SnCl₄) or to attack at the C₅–C₆ protecting group with release of acetone (e.g. by CF₃CO₂H, SO₂ or CH₃COCl). Pesticidal and fungicidal activities of compound 3(R?R′?Ph) as well as of 1,2:5,6-di-O-isopropylidene-3-O(triphenylstannylmethyl)-α-D-glucofuranose (compound 2, R?Ph) and methyl 4, 6-O-benzylidene-2-deoxy-2-triphenylstannyl-α-D-altropyranoside (compound 1, R?Ph) are reported.     

Synthesis of backbone modified cyclic peptides bearing dipicolylamino sidearms

Three analogues of the Lissoclinum class of cyclic peptides, bearing dipicolylamino functionalised side chains, have been synthesised using a stepwise approach followed by macrocyclisation. Attempts to incorporate dipicolylamino functionalised side chains prior to peptide synthesis resulted in epimerisation, but this was overcome by functionalising the ornithine side chains with dipicolylamino groups after the macrocyclisation reaction.     

Thermodynamic, kinetic, and computational study of heavier chalcogen (S, Se, and Te) terminal multiple bonds to molybdenum, carbon, and phosphorus

Enthalpies of chalcogen atom transfer to Mo(N[t-Bu]Ar)3, where Ar = 3,5-C6H3Me2, and to IPr (defined as bis-(2,6-isopropylphenyl)imidazol-2-ylidene) have been measured by solution calorimetry leading to bond energy estimates (kcal/mol) for EMo(N[t-Bu]Ar)3 (E = S, 115; Se, 87; Te, 64) and EIPr (E = S, 102; Se, 77; Te, 53). The enthalpy of S-atom transfer to PMo(N[ t-Bu]Ar) 3 generating SPMo(N[t-Bu]Ar)3 has been measured, yielding a value of only 78 kcal/mol. The kinetics of combination of Mo(N[t-Bu]Ar)3 with SMo(N[t-Bu]Ar)3 yielding (mu-S)[Mo(N[t-Bu]Ar)3]2 have been studied, and yield activation parameters Delta H (double dagger) = 4.7 +/- 1 kcal/mol and Delta S (double dagger) = -33 +/- 5 eu. Equilibrium studies for the same reaction yielded thermochemical parameters Delta H degrees = -18.6 +/- 3.2 kcal/mol and Delta S degrees = -56.2 +/- 10.5 eu. The large negative entropy of formation of (mu-S)[Mo(N[t-Bu]Ar)3]2 is interpreted in terms of the crowded molecular structure of this complex as revealed by X-ray crystallography. The crystal structure of Te-atom transfer agent TePCy3 is also reported. Quantum chemical calculations were used to make bond energy predictions as well as to probe terminal chalcogen bonding in terms of an energy partitioning analysis.