Context : Since most high- and intermediate-mass protostars are at great distance and form in clusters , high linear resolution observations are needed to investigate their physical properties .

Aims : To study the gas in the innermost region around the protostars in the proto-cluster IRAS 05358+3543 , we observed the source in several transitions of methanol and other molecular species with the Plateau de Bure Interferometer and the Submillimeter Array , reaching a linear resolution of 1100 AU .

Methods : We determine the kinetic temperature of the gas around the protostars through an LVG and LTE analysis of their molecular emission ; the column densities of CH _ { 3 } OH , CH _ { 3 } CN and SO _ { 2 } are also derived .
Constrains on the density of the gas are estimated for two of the protostellar cores .

Results : We find that the dust condensations are in various evolutionary stages .
The powerhouse of the cluster , mm1a , harbours a hot core with T \sim 220 ~ { } ( 75 < T < 330 ) K. A double-peaked profile is detected in several transitions toward mm1a , and we found a velocity gradient along a linear structure which could be perpendicular to one of the outflows from the vicinity of mm1a .
Since the size of the double-peaked emission is less than 1100 AU , we suggest that mm1a might host a massive circumstellar disk .
The other sources are in earlier stages of star formation .
The least active source , mm3 , could be a starless massive core , since it is cold ( T < 20 K ) , with a large reservoir of accreting material ( M \sim 19 ~ { } M _ { \odot } ) , but no molecular emission peaks on it .

Conclusions :